BMW Airhead (& some twins prior to Airheads) Motorcycles
Model differences over the years. Technical details of importance.
Including a chart on weights and capacities.
Plus information to identify the model/year, if you do not have a serial number, etc.
© Copyright 2018, R. Fleischer
Identifying the year of production by serial and/or VIN number:
Beginning in 1980, and the process not completed until sometime in 1981, U.S.A.-shipped bikes from BMW changed from a pure serial number to a Vehicle Identification Number (VIN). This new type of 'number' is a combination of numerals and alphabet letters, and the total length is always 17 characters. The tenth position character (beginning from the left) is the official production year. As an example, for 1980, that was an "A". Each year following was one letter further in the alphabet. I, O, Q, U, Z, were all skipped. Beginning in 2001, a digit was used, with 2001 being 1, 2002 being 2, etc. Non-U.S. models might not use the 17 character VIN number system. In every instance, BMW records can use the last seven characters, which are almost always just numbers to identify the year and model; and, indirectly, the color and how equipped when it left the factory. All brands of motor vehicles sold in the USA since the 1980-1981 transition era use the same 17 character VIN system.
For BMW vehicles, there can be confusion between the year of manufacture and the model year. This has sometimes caused problems with titles and registrations with various States. The actual "model year" motorcycle could have been produced near the end of the prior calendar year, due to the BMW company-wide vacation month in August and restart of production immediately after that vacation, in September. There are exceptions & anomalies ...most of these are such as when a BMW bike was manufactured even earlier and mysteriously is identified by BMW as the following year's model. This has happened with some Airheads and some Classic K bikes now and then. There is sometimes additional confusion, because, for 1984, BMW stopped stamping the last 7 characters of the 17 character VIN, always a 7 digit number, next to the oil dipstick of all engines.
For very considerably more information about VIN and Serial numbers, how to read all 17 characters of VIN's, the sequencing, the anomalies, etc. see the following article: http://bmwmotorcycletech.info/IDnumbrs.htm
"Airheads", for the purpose of this website, and this article, mean BMW motorcycles with the 2 cylinder boxer-layout engine style with two valves in each head, as produced beginning 12/1969 as 1970 /5 models. Airheads are generally considered as being in production into 1995 and possibly a few into 1996. Airheads are not the other boxer type motors that BMW produced, slangly called the Oilhead, Hexhead, etc. Those are considered air and oil cooled, and have a very different type of engine design, which are also all fuel injected. Slash 2 is used generically, to mean the models more or less immediately before the Airheads; that is, before 1970. I don't get deeply into them. They were generally produced in the fifties and sixties.
The details in this article are not to be considered to list every year's change. I will add details to this article now and then.
Models prior to 1970:
This article you are reading has, in this section, information on models prior to the /5. BMW made some radically different bikes from 1923 to the end of WWII. Overhead cams, single cams, dual cams, supercharged, besides the more pedestrian models, including single cylinder models that paid the bills. For a discussion of of these early bikes, refer to:
4. http://www.benchmarkworks.com/ A major source for technical information, parts, etc. for early BMW's. Owned by Craig Vechorik, also known as 'Vetch'. There are few knowledgeable folks having a business that specializes in working on or supplying parts and information for pre-1970 BMW motorcycles, Vetch is one of them. Benchmarkworks is at 3400 Earles Fork Road, Sturgis, MS, 39769 USA, telephone: (662) 465-6444
5. The book: Illustrated BMW Motorcycle Buyer's Guide, by Stefan Knittel and Roland Slabon
If you have a /2, you can install a 12 volt alternator and lamps conversion for much better lighting. Coil ignition can be installed (not needed IMHO). Using the best modern partial or even full synthetic oils, you can extend the time between /2 crankshaft slinger cleanings, although just how much is questionable, and depends on engine condition, particularly engine blow-by. A worn engine allows more blowby, more contaminants into the oil, including more carbon, which fills the slingers faster. You surely do not want the slingers to fill totally...which causes oil starvation to some parts of the engine. Use of a quality oil with ZDDP or ZDTP is helpful.
The internals of the wheels of the /2 era bikes are very similar in basic design to the /5 and even into /6 airheads, but the /2 era bikes had larger diameter axles and frames that flexed less. This was because the motorcycles were designed to allow for sidecar use. The /2 era ended BMW's practice of "sidecar fittings as standard". This was made doubly so with the abandonment of the adjustable trail Earles leading link fork, ...which had been an option, or standard, depending on the model and ordering by the dealer. The /2 era bikes steering heads had ball bearings, which were not as good as the /5 and later tapered bearings, but they are installable. The /2 series ended the use of the very nice-looking bars-end turn signal housings. If you have, or are contemplating, the ownership of a pre-Airhead BMW motorcycle, be sure to extensively read up on them.
The Airheads, general information:
"Airheads" are twin opposed cylinder air-cooled motorcycles manufactured between the end of 1969 (the beginning was the 1970 year model) and the end of production in 1995. For the 1970 models, BMW made huge changes to their production bikes, especially of note was the changes to the motor and frame. They also completely dropped, even as an option, their version of a leading link type front fork which is called the Earles Fork. The last such huge changes were arguably in the R5 of 1936. The motor for 1970 had plain bearings lubricated by a high pressure system & there was a pleated paper oil filter. The camshaft position was changed to below the crankshaft. Previous motors had roller bearings for crankshaft & camshafts, low pressure oiling systems, and some form of "filtering" that is generally referred to as a slinger or slingers. The electrical system had major changes. There is a long list of various changes ....and I will get into most of the changes, later herein.
The use of the separate rear frame on the /5 and later (most models) causes fitment problems, not nasty ones though, when fitting a sidecar to a /5 and later Airhead, which was specifically not officially allowed. The separate rear frame structure, on those models having it, do cause some flexing, which was improved over the years of production. The /5 Airheads had a thinner front axle diameter than later Airheads (14 mm versus 17 mm); and some bending had been seen under severe conditions, hence the later factory change from 14 to 17 mm. This was easily accomplished by BMW by simply changing the internal spacers of the wheels, and the hole size in the fork lower legs.
There are websites and groups devoted to the early bikes. /5, /2, G/S, ST owners ....and some others ....also have their own websites. See this page: http://bmwmotorcycletech.info/url.htm
The primary immediate response source of technical information for all BMW AIRHEAD boxer models, made from 12/1969 to 1995, is not the single model websites in the above short paragraph, but the Airheads LIST: http://bmwmotorcycletech.info/technical-articles-list.htm for information on how to become a Member of the Airheads LIST, which is free.
BMW has tended to find ways to use up old parts bins stocks, and has sometimes shipped various combinations of components; this was particularly so in the 1973-1976 era. It is fairly easy to swap many parts on many or all Airheads. While there is a lot of interchangeability possible on parts & components, this is not to be taken that all can be interchanged, or that just because some will physically fit, it is wise move. There are very specific problems, or concerns, in interchanging many items. It is possible to put some items from other BMW bike lines into Airheads. The Classic K-bike front ends & brakes, for example. Actually, very substantially-built forks from other makes can be installed, as can alternators from Moto-Guzzi, Ducati, etc. Those thinking of swapping Airhead cylinders, cylinder heads, transmissions, rear drives, etc., can consult the Airheads internet LIST for expert advice, although there is information in my #60-x articles, & information on other things, like drive-shafts, rear drives, fuel tanks & seats, etc., found scattered in the appropriate areas on my website. I also have an article on modifications for performance: http://bmwmotorcycletech.info/mod4performance.htm
Not all models were shipped to the U.S.A. in any given year. Only a few are important, one of which is that BMW stopped shipping R100-engined bikes to the USA for a couple of years in the 1980's; and the R45 bikes (both versions) were never imported into the USA by BMW. Some of these various not-imported bikes are seen now & then in the USA, including the later R80GS and R80GS-PD with Paralever; the R65GS, R80R, 1995-1996 R100RT Classic (questionable about the importation of those, and note I listed 1996!!) and R100GS PD-Classic.
Here is a good website page, showing a chronological index for BMW motorcycles with some specifications for each model. If you click on a model, you get a lot more information. Unfortunately, the site does not separate out Euro vs USA versions, and the site also includes the pre-Airheads, and the later models too.
The Airheads, part 1:
There have been a large number of changes to the Airheads over the years, yet there remained mostly similarities. This article does not show all changes, as there are too many. Cosmetics and finer details like tank shapes & fits; seats fits, etc. ... are generally not included in this article.
In late 1969 BMW stopped manufacturing all prior models and began manufacturing only boxer twins, beginning with the /5 series. The /5 was a radical departure from their previous motorcycles. Although BMW had conventional telescopic & leading link (Earles) forks on previous models, now only telescopic was offered. The frame was considerably modified, and no longer wrapped to the rear. A separate bolted-on rear sub-frame was now used. I do not consider the new rear sub-frame an improvement. As the years rolled on, BMW beefed up the frame to improve handling, but the separate rear subframe continued for some time. It contributed to the famous 'rubber cow' effect. Early models exhibited that effect much more than later models, and the Monolever and Paralever models had little of it.
The rear suspension plunger design was abandoned in favor of a swing-arm design. The plunger design is better for sidecar use. The /5 and every Airhead model ...and all other BMW motorcycle models made since the end of 1969 ....were not designed for sidecar use; but most have had sidecars put on them successfully.
The new engine design had a considerable number of changes. Mechanically, the biggest change was to move the camshaft location to below the cylinders, this improved lubrication. The pushrod tubes delivered the oil from the top ends to the camshaft lobes by draining downward inside the pushrod tubes. The engine internal oiling system was modified. An oil filter was incorporated, where only crankshaft 'slingers' were used before. This new design eliminated the need to remove the crankshaft every 30,000 miles (approximately), for slingers cleaning or replacement. The 6 volt system was changed to 12 volts and the magneto was abandoned in favor of points & coil ignition. A starter motor was added. In general, the longevity of the motor, and mileage between serious service intervals, was substantially increased. BMW motorcycles became more popular in the USA and began to get a more and more well-deserved reputation for being quiet, competent, and needing less service, and having fewer problems than most other makes.
The /5 came with a 180 watt 3-phase alternator. After the /5, higher capacity alternators became standard with the introduction of the /6 series. Certain early /6 series 280 watt alternators will fit the /5.
The first /5 models had a shorter wheelbase (easily seen by a quick glance at the rear area of the black colored driveshaft housing, it has no welded section a few inches from the flange end). This early /5 SWB (Short Wheel Base) and to a more modest amount the early R65 (also short wheel base, but production began on the R65 much later, in late 1978) could (not will), have some potential for instability under some specific types of riding....and in particular if a fork-mounted windscreen was installed (or a big bat-wing type) and worse if the rider had considerable weight aft of the rear axle and speed was high; big saddlebags and a rear trunk made things worse. BMW elected to go to the LWB (Long Wheel Base) in mid-1973, and for the R65 it was in the eighties, but no R65 model of any year had the same level of possible instabilities as the SWB /5. There is an article on this subject: http://bmwmotorcycletech.info/instability.htm. You can see the welded-in section, used for many years after it became standard. The LWB (Long Wheel Base) also allowed for a bigger battery. My personal preference is the SWB. It feels quicker-handling. BMW incorporated the LWB in mid-1973. There was also the later addition of an internally cushioned driveshaft. The cushioning was provided by smooth-finished two-part mating-cams, whose actions were backed up by a very strong spring. It is better for the transmission to have the "cush driveshaft", but not at all critical, and not required at all if shifting is done very smoothly. There are some further advantages to the LWB models, including more stability with aft loading, better able to handle windscreens, and capability for a larger battery...the original being small in size. The SWB has a somewhat higher torque feeling if the throttle is suddenly snapped off, and this is more noticeable in turns.
While not getting into it any deeper than a mention here, there was no hue and cry about instabilities at speed on the SWB R65 ...which out-handled any stock /5 ... & some of which was due to the top triple clamp being very beefy; even though the 18" front tire was possibly a negative. This is all arguable, of course.
The /5 bikes had 10 mm flywheel bolts, and the 1974 /6 also did ...these could be twisted off from serious rider abuse during riding. Some slightly later /6 may have them ...perhaps into early 1975. After this, the bolts were 11 mm. The bolt torques vary, and using the torque information on this website is a good idea.
In identifying a /5 engine block, there is an eyebrow cutout on the front face of the engine block. It is solid from 1974.
Obviously, these are not viewable on a motorcycle with the timing chest & outer cover still on the engine.
The /5 SWB bikes and /5 LWB motorcycles use different saddlebag mounts. The early R65 can be fitted with its own bag mounts, or /5 mounts adapted, and vice versa.
The /5 with its 180 watt alternator came with a 40/45 watt non-halogen headlight. BMW offered a kit to convert to the much better H4 lamp, but the kit is NLA. Converting the headlight, in some good manner, is an excellent thing to do for your /5 motorcycle. You have to change the lens too, or the light pattern is spread about rather poorly (but, see the next paragraph). You can easily adapt the R65 headlight parts to a /5. Conversion gives vastly better lighting at night, using a 55/60 watt H4 halogen lamp.
Later bikes got rid of the clip method of holding the bottom of the headlight chrome ring ...which sometimes allowed a headlight assembly to fall and be damaged. Modification of early chrome rings to avoid loosing the ring, headlight, etc., is a good idea. The http://bmwmotorcycletech.info/lamps.htm article has information on a H4 type lamp that will work with the original /5 reflector and base.
The /5 models came with a crankshaft rear main-seal that tended to leak after enough mileage & maybe dirty oil helped that along. BMW has made a number of mainseal changes over the years, & considering mileage & servicing, the chances are low to modest that you will find an original type of white seal. With the /6, BMW added an O-ring inside the flywheel bore & with the /7 came a metal cap and the same O-ring continued. The final version of the main seal has a Teflon section, & works very well, & fits all Airhead models.
The automatic timing unit (ATU) for the ignition was changed a few times too during the /5 era. The final version was in 1981.
Here are a few more differences that you may want to know about, between the /5 and the /6:
Front wheel and brake; headlight bucket deleted from prior speedometer-tach integration in favor of an instrument pod; fuel tank (they look alike but the underside is different to allow for front brake master cylinder clearance); valve gear is modified; transmission went from 4 speed to 5 speed; battery area became larger (first expanded with the LWB /5); starter relay function & internals vastly different; headlight relay installed (and function on early /6 not same for that relay as later uses of it); turn signals changed; wiring harness was radically changed; flasher (Trafficator relay); seat was different, ETC. The /5 original cables did not have the plastic linings of the later cables, thus, if you have originally shipped /5 control cables, you could oil them as a last resort if they are acting up.
The 1974 model year introduced the /6 bike, and 1974 was a not-so-good year. This newly introduced /6 bike had carry-overs from the /5, & new problems. The 1974 still had the 10 mm flywheel bolts; shearing them off could ruin a crankshaft, sometimes just messed up the threads. These bolts tended to shear off on the R90S in particular. Fixed for 1975 with the larger bolts, which means that BMW changed the crankshaft & the flywheel. A 5 speed transmission was introduced....and it had problems. The pawl springs would break, the input kick-starter special gear was soft & wore (don't use the kickstarter on a 1974 unmodified transmission unless actually needed) ...and the metal shredded into the gearbox & damaged the bearings. The shift forks were too wide & gear dogs broke. You can't purchase the gear alone, only the whole cluster assembly...and the original one is no longer available. That means that you have to install the 17.5° late model items, & that is $$$. There is a huge amount more on transmissions here: http://bmwmotorcycletech.info/transmission.htm. Finding neutral was often somewhat difficult, overshifts also happened, & most problems were not fixed until 1976. As I mentioned, some 1974 transmission parts are now NLA, & brand new transmissions or a good later model are often the best answer to trying to rebuild a 1974 transmission. The transmissions are directly interchangeable, that is, they will physically fit and operate OK, including the earlier /5 era 4 speed, all the way to 1980.
The handlebar controls of the 1974 were a carryover (of sorts) from the /5. Some of these parts were part /5 types and part /6 types, and NLA, although later controls certainly fit. These switches may look like /5, but have different wiring. The 1974 switches are no longer available. The handlebar right side assembly is rather difficult to convert to a handlebar master cylinder. The 1974 front axle was still 14 mm, in bushings (the 17 mm axle came a year later, as a full fix in 1976 models). Under some severe usage, the 14 mm front axle could bend. You can make simple changes in the wheels innards to accommodate the later fork lowers and 17 mm axle. The 1974, only, had "strange" fork tubes/lowers (1974 lowers are NLA); the 1974 model (only) had a one-year-only type of lower fork leg, and are NLA, and later versions must be used for repairs. Engines tended to vibrate lightly around 4000-4600 rpm. The frames were a bit weak, with the 1975 being better, and the 1977 better yet, with more substantial bracing.
Compared to later models, the 1974 had a somewhat more rubbery feel, due to the weaker frame...the frame was beefed up in the late seventies. Possibly some crankshafts are marginal, causing vibration. The 1974 retained the 97 mm crankcase port for the cylinders (the 99 mm crankcase port and matching cylinders came during 1975, and the cylinders are also 0.5 mm longer), and new cylinders are NLA. BMW made changes to the cylinders and case so that O-rings could be fitted into a recess at the top engine studs fitment at the case, where the high pressure oil gallery supplies oil to the cylinder head.
The 1976 incorporated many other upgrades as was noted earlier, and these included larger pushrod tubes, pushrod changes, engine case cylinder hole size increase to 99 mm. Later engine's Nikasil cylinders will fit.
BMW made their "Hot-Rod" (or, call it the sporty model) R90S starting with production at the very end of 1973, for model year 1974. Production ceased in mid-1976. The bike was the only BMW that ever came with Del'Orto carburetors. Partly due to its very fancy and hard to duplicate paint job, partly due to its history of racing at Daytona, partly due to the small fairing, etc., the R90S became a cult collectors item. The very first models were the fanciest looking. The R90S had a compression ratio of 9.5:1. Performance was about as good as the Euro version of the later R100S/R100RS/R100RT. During production of the R90S, the factory began deleting things. Fewer chrome fasteners, chrome in the front of the horn, the taped pin stripes became painted. The 5 position ignition switch changed to the standard 3 position type, mirror stalks became straight, no kickstarter (orderable though). There were also some improvements along the way, such as went with the rest of the /6 line, such as drilled brake rotors and a slightly more powerful starter.
In 1977 BMW made a R75/7 model, the last of the 750 models. Production was between the end of 1976 and end of 1977. This was a very good motorcycle. In 1977-1978 BMW also finally installed the electronic tachometer (the motorcycles had already been wired-for them) in the bike. 1977 bikes had good horsepower output, good torque.
The transmissions had gusset reinforcement running only from front to rear (none left-right). Beginning in 79 the gusset reinforcements at the bottom of the case were cross hatch like a crossword puzzle. Changed was the shift linkage. It now pivoted from the footrest, and was more positive. Camshaft timing changed in this 1977-1978 change era, by changing the camshaft sprocket keyway, amounting to a 3° advance in the cam, which means 6° advance in reference to the crankshaft. This was the beginning of the emissions changes, that were not all incorporated at the same time ...much more happened later-on.
BMW changed the internal driveshaft to a 'cush' type, incorporating a very stiff short spring and a dual cam, that made shifting much nicer. The driveshaft housing was still the tapered type, which lasted until 1981, when the housing changed to a straight tube. At one time, BMW offered a 'kit' to incorporate the cush driveshaft into earlier models. Note that if you try to install a 1980+ driveshaft into the earlier style of driveshaft housing, a bit of grinding on the shaft will be necessary. The piston pin 'keepers' were changed to external clip types. The handlebars got the padded centers on all models, as of 1979, as previously it was just on the R100RS. Note that the RS and RT got Brembo rear disc brakes, but the front brakes remained ATE swinging calipers. The RS and RT also got the oil cooler as standard. BMW modified the cylinders base area to accept a very large rubber O-ring.
Also in 1979 came a different system of driving the ignition points; the "canister"; sometimes called 'the bean can'. The canister contained points for only the 1979 and 1980 years, and worked well. In my opinion, the lack of a lubrication felt was not a good idea and owners should be sure the points cam is very lightly greased with a high temperature grease, such as the special Bosch grease that is designed for this purpose for the earlier models. In 1981 the same canister was used to house the trigger for the new electronic ignition. There is nothing wrong with any of the points-types ignitions BMW used. The points ignitions are cheap, fixable anyplace, but you do have to check the points every 5000 miles for gap, lubrication of the cam/felt on the early model (no felt for canister models), and engine timing setting...all relatively easy to do. Points last about 15,000 to 20,000 miles, then must be replaced. Aftermarket points amplifiers or boosters are available that reduce the current through the points, and I recommend them. If the points are installed carefully, and kept quite lightly lubricated at the felt pad (pre-1979) and at the points cam, then with a booster or amplifier, the points life can triple, or even more, yet be easily field-repairable in a few minutes, even if the booster-amplifier should fail. The 1981+ electronic ignition is quite reliable, very powerful; but, for reliability you must not ever pull off the spark plug caps whilst running (bad idea for any 1970+ model actually). Some literature is flat out wrong about it being OK to do that on 1970 and later models. Some BMW models such as the R80ST and R80G/S had a single coil with dual towers, instead of the prior two each 6 volt single tower coils, and the early single coils with dual towers tended to fail (gray plastic bodied ones). All very late BMW airheads have a single, 12 volt, dual output coil, but the later versions are more reliable than earlier ones. Some early models in the 1980's had two separate 6 volt coils in series, just like much earlier models, and these were very reliable. You can read all about these things at these articles:
From 1980, BMW made a change in the oiling system that is cast into the block: http://bmwmotorcycletech.info/oilsketch.htm. There is more than one sketch on that page to look at. It is not anything critical at all, but to identify the engine blocks you must remove the transmission and clutch, and stamped into the rear of the engine block is a triangle with a N in it.
BMW made various changes to the valve gear over a long period of time. The /5 had sleeve bushings in the rocker arms, the rocker arms were not positively located, and more care in adjusting the valves squareness of the rocker blocks, etc., was needed. BMW made changes to more positively locate those rocker blocks, and installed needle bearings, and in 1985 came the last big change, to a shim method of setting rocker end play, which helped reduce valve noise even more; but the rockers were narrowed. BMW also added 24 small black rubber inserts into the head fins, to eliminate fin ringing. All valve gear changes, with few exceptions, can be installed in part, or in total, in any earlier model. These updates are not mandatory.
It was in 1980 that BMW lowered the compression ratio of the bikes coming to the USA, and, the air cleaner housing was changed to the rectangular type, and Pulse Air emissions controls were incorporated, but this did not happen the same way and time slot for the Euro machines. For the USA, 85 mph speedometers were fitted; which were often quite accurate, in speed indication (odometer readouts have always been accurate). The carburetor and choke cables, previously twinned, were now single cables at the bars, and a T box was incorporated, located under the fuel tank. Contrary to what some believe, it really was a good change, enabling better cable synchronization, and more stable synchronization, even when the bars are turned.
A fairly radical change was made to the clutch in 1981, together with installing the much better Nikasil cylinders. The clutch, including the 'flywheel' which was renamed a Clutch Carrier, was now vastly lighter, and changes made for a much easier clutch lever pull. Prior to 1981 clutch lever pull was fairly stiff, many folks with less strong hands would complain. There is a Easy Clutch conversion kit that is very simple to install for the early heavy clutch, see the above Craig Vechorik's website. Installation of that is a tradeoff. Note that the 1981 (only) clutch was weak, and some 'blew up'. Since model years crossover with production time, it is usually called 1981, but I consider it the 1980 and 1981. The earliest diaphragm springs were weak for hard use and discs were poor and blew up. 1981 clutches should be updated when they are overhauled. Anyone with an original 1981 clutch area being worked on should update to the later parts. There is an extensive clutch article on this website. Note that there were some soft splines on these clutch discs, which can cause failure of transmission input shaft splines.
Note that pre-1981 and 1981+ transmissions have different input shaft lengths, so take this into account if substituting transmissions. Shafts can be changed at $$$ cost (or, much more cheaply, shortened on the longer shaft on earlier transmissions) of course; as can clutch parts, to provide even more interchangeability. Another problem to be considered is that Paralever bikes have different transmission mountings.
Nikasil or Galnikal:
Nikasil or Galnikal ...is a special coating in the cylinders. That coating, which is extremely tough, wears extremely slowly. The cylinders could now be made of all-aluminum, the older iron sleeves eliminated. Cooling was improved; the new cylinders last almost forever, oil burning is reduced by not only the minimized wear but that the cylinder roundness and taper is easier to control tightly, compression stays higher over time; and every aspect of roundness, taper, etc., is improved for the long term. These cylinders can theoretically be bored to a larger diameter and if damaged may possibly be reclaimed by one of several specialist companies. I do not recommend boring (or other machining) and plating unless by such a specialist. Information in my http://bmwmotorcycletech.info/references.htm page, has listings of who does that sort of thing. If you can obtain oversize pistons, you might be able to machine and recoat oversize. BMW does not offer over-sizes, only fitted sizes for these cylinders. Other manufacturers may; particularly from Germany.
For the earlier iron cylinders, many kinds and sizes of pistons are available, and the cylinders can be bored conventionally ....preferably by someone who knows BMW airhead cylinders! ...as boring can be tricky to do correctly on the older iron sleeved cylinders, and pressure plates are a must. Note that the old iron cylinders can be bored and Nikasil applied in some circumstances, but I don't recommend boring the early R100 cylinders, as the material will become thin enough to possibly give problems with out-of-roundness, etc. Individual cases will vary however, and in some instances the Nikasil or similar process will work.
BMW changed the ignition from a points type, to a full electronics type, incorporating a Hall element inside the canister. The ignition is very powerful, and use of 5000 ohm spark plug caps is mandatory or the ignition can fail. Like on all Airheads, the ignition must never be on if the spark plugs and caps are not in place; or, the inside connection of the caps grounded. A few of the early electronic ignitions failed early-on. The oil pan was made deeper, and it could hold a bit more oil, and now incorporated a surge-baffle. The exhaust pipes became 38 mm, and the second crossover pipe was added to twin shock models.
BMW also changed the internal design of the front forks; and, IMO, not for the better. The early fork changes tended to give lots of noises, and BMW did numerous changes, over time, to fix these things. By 1983, the problems went away, but the forks are still not as sophisticated, and not in operation either, as the ones from the 1970's.
There were frame changes in 1981 and transmission internals changed. Some of the input shaft gears in the transmission broke, or otherwise failed. This problem was fixed in stages by BMW. The 1981 model had a poorly designed center-stand, and it took a lot of effort to use, some of this was fixed in 1982, and a kit was sold by BMW to fix the center-stand problems of the early eighties. A few of the early Nikasil cylinders had coatings that peeled off.
Sometime in 1981 BMW redesigned some of the transmission internals; the most known of which was the incorporation of a 'Shift Kit', which fixed problems of overshifting and false neutrals mostly due to the lighter clutch assembly, but there were reliability improvements too. The kit is NLA, but the $$$ parts are available. The kit was phased in by BMW, and all Airheads probably had the kit by late 1982. Complete description of details are in my transmission article http://bmwmotorcycletech.info/transmission.htm
****Note that a few engine (or transmissions??) castings did not have correct dimensions, and the input shafts would continually fail. There has never been a fix. If input shafts and clutches continually are having a problem, you may have that situation.
In 1983-84 (1982 in Europe) an R80ST model was produced with a single sided rear drive called a Monolever. There was a G/S model which was similar, with a bash pan and larger 21" front wheel, meant for on/off road, produced from 1980, continued to 1988, which also had the single sided rear end. Monolevers are relatively easy to fit to twin shock bikes, although not totally a simple bolt-up. Single sided rear ends have both advantages, and disadvantages. They use only one rear shock unit (aftermarket shocks are usually much better than the stock BMW ones), and tire/wheel removal is vastly easier. Wheels of both 3 and 4 bolts were offered, depending on year and model. The forces are applied more forward, and handling is considerably improved, particularly when quite aggressive. The rear subframe on other models is no longer a rubber-cow "problem". There is no wheel bearing as such, that function taken over by the crown gear bearing inside the rear drive; the disadvantage to that is that forces are applied to the bearing/type that cause wear; while the tapered wheel bearings of the twin shock models can last forever. When that bearing does wear enough, it is much more costly to replace, and a rear drive overhaul is usually done. Another disadvantage is that a twin-shock rear end is theoretically better suited for use with a sidecar, but many a Monoshock or Paralever bike is pulling a sidecar, with few or no problems.
A few Monolever rear drives were not produced correctly, and failed early. Some were also assembled with the cardan cover sealed by a sealant and not a paper gasket, and unless the rear drive is re-shimmed, the same method must be used.
All the 1981+ to 1984 models had problems with the valve seats. This was different than the earlier models, which, upon receiving only unleaded fuels, tended to start having problems, which resulted in closing-up of valve clearances (particularly the exhaust). This same closing-up occurred with the 1981-1984, but this time it was not the unleaded fuel, but the wrong material selected by BMW for the new exhaust valve seats. The final fix occurred in 1985 with another new type valve seat material, which is how all models should be fixed. Mostly the problems were with the hotter-running R100 series models. Fewer problems were seen with the cooler-running R80 series models, and fewer yet with the R65.
In 1984 BMW had a Last Edition model R100RT for the USA, but BMW brought back the R100RT a few years later. There was quite a bit of bad feeling about it all & BMW offered new helmets to 'compensate', ...but it was a mess. For the most part, the 1983 & 1984 bikes are mechanically the same.
Faired models were produced from late 1976 but did not come to the USA for several years, when the R100RS finally arrived. The R100RT was first fully faired model to come to the USA (although some describe the RS as fully faired), and made quite a splash in the U.S. in 1979. This 'splash' was all over the print media; the wind-tunnel designed fairing added a lot of weather protection, etc. The RS and RT were very unique for the era, compared to the naked bikes in production, or ones with bat style front part-fairings/windscreens that usually were added. The Avon fairings had been available for BMW bikes as early as the /5 era, and fairings for other BMW bikes were available for even the 1950's and 1960s, but not from the factory as an integrated motorcycle. The RS/RT fairings were designed and tested using a wind-tunnel; resulting in a rather low-lift, and relatively low drag too.....so high speed cruising was fairly nice. The later-available Hannigan STe fairing was slipperier, that is, it had less drag (and less lift too!), but was only available as an aftermarket item.
The front brakes and master cylinder were all changed drastically, and now Brembo brakes were installed and the master cylinder was a Maguro type. Due to how the calipers were mounted, etc., the assembly, over-all, was lighter, probably improving handling ....but the brakes had better stopping power too. Asbestos was not used in the pads, which were a metallic-containing type, which had a very long life & worked well in wet weather. BMW kept its own SS perforated discs.
In the 1980 to approx. 1985+ era, the Euro versions had some changes I have not set down here, such as some models having a different compression ratio, changes in the controls switching and wiring, etc. I have already mentioned that the Euro bikes did not get the full-blown emissions setup and same rectangular airbox ....at least not in the very beginning (1980+-). In addition, certain models did not have the same changes incorporated at the same time (example: R80RT versus R100RT).1987:
The Paralever bearings can be 'upgraded' (IMO they are market hype!) with an aftermarket solid bearing that looks quite sturdy; yet, in my opinion it is not really an improvement, and can create new problems!! I do not recommend them. Yes, I know that this means I am at odds with dealerships and some aftermarket independent servicers (who sell them for a profit).
The Airhead Paralever bikes occasionally have rear drive troubles. Opinions differ on why and how these troubles come about. Opinions are such as improper shimming of the crown gear and/or use of overly high viscosity oils. There are also those who think that the Paralever design puts extra forces onto the transmission output shaft, making worse the circlip-less versions of the transmission. That is also my belief.
In the late 1980's, BMW made some subtle changes. One such is the incorporation of a "step" on the cylinder spigots, with matching machining on the engine casting.
Last of the Airheads:
Some models were produced into the 1990's. R80GS, R80, R80RT, R100RS, R100RT (to 1995). New models, the R80R and the R100R, were produced in three versions, R80R, R100R, R100R Mystic, and R100R Classic. Produced between 1992 and 1996. There was also a R100RT Classic produced in 1995-1996 that was never imported to the USA. There were some Authorities bikes (Police bikes) produced in this period, and possibly for some months later. Some of these various bikes, besides as noted above, but see early in this article, were not imported by BMW into the USA. The R100R bikes were imported to the USA, all supposedly had the latest fixes, of which there were not many. These "R" bikes had unique instrument pods; and, in some ways, the motorcycles were similar to the GS models. Tubeless GS style wire wheels and a unique instrument pod, and other things were standard. However, see the next paragraph!
It is possible for Airhead models of 1984 to 1995, no matter what BMW says in its literature, to not have a circlip at the 5th gear in the transmission. This can be serious and costly to fix if you have a problem with the transmission. See the following article which explains it all, in depth. http://bmwmotorcycletech.info/transmission.htm
The article also has a listing of transmissions, serial numbers, testing, very full description of problems, lots more, besides being a transmission repair article.
The Airheads, part 2:
BMW Airheads have a nominal displacement, with the actual displacement being slightly lower than their model number indicates, this likely was done on purpose, so the displacement is always just barely under the next level for countries that tax by displacement; and, perhaps to allow for slight overboring.
The /5 bikes were produced as R50/5 (500cc); R60/5 (600cc) and R75/5 (750cc).
Other BMW twins are: 450 cc (R45 series); 650 cc (R65 series); 800 cc (R80 series); 900 cc (R90 series); 1000 cc (R100 series).
All the twin cylinder engines until production ceased in 1995 had two "opposed" cylinders. The cylinders are not directly opposite, but offset slightly, as the piston rods are located side-by-side. For this reason the engines can not be 100% balanced, contrary to popular belief that the engines are 'inherently' perfectly balanced.
The /5 bikes had the classic bullet headlight and instrument shell and used a 'stick' one key fits all type of ignition key. Thus, the only real locking security is a standard type of key lock located in the steering head area.
The speedometer/tachometer unit in the /5 is a fun and games job of removing for service. After the /5, the lovely bullet style headlight shell that contained the headlight and the combined tachometer-speedometer was abandoned, in favor of one of two basic styles of instrument pods.
The /5, only, had a starter relay, mounted under the tank, that was specially designed and wired to prevent the starter from being energized and thus engaged, if the engine was running at idle ...or a bit above (it was wired to the alternator output). That relay had a transistor circuit inside it that gave problems that could seem to indicate that the battery was near dead, and the sound produced is called 'the cricket'. This could happen when cold, or with even a slightly discharged battery, or both. A simple modification to the relay innards will cure the problem. There is an article on this website covering this in considerable detail, http://bmwmotorcycletech.info/slash5cricket.htm. Later Airheads had a more conventional relay, without the transistor, and there was no protection against running the starter motor with the engine running ....although a combination of a switch on the handlebars that was part of the left-side clutch lever assembly; and, a two-terminal neutral switch that had multiple functions, tended to keep one from using the starter at the wrong time.
The Bing CV carburetor was introduced on the R75/5. The earliest CV versions, BING model plate ending in /1, /2, and the commonly used one on the R75/5, the /3 and /4, had many problems. There is an article devoted to those early carburetors on this website: http://bmwmotorcycletech.info/earlybingR75CV.htm
The next carburetors, the /9 and /10, were much better. The later carburetors as used on the R75/7 would be very good.
As earlier noted, the /5 production started with what is called the Short Wheel Base models (SWB). Under some hard riding in very specific circumstances, which you'll probably not figure out how to duplicate (unless you also have a steering mounted fairing and maybe some rear area large items or weight), instability was noted, and in mid-1973 BMW lengthened the subframe and the driveshaft/driveshaft housing, with a very noticeable welded-in 2 inch section, that welded section was kept for some years, even into the /6 production, until, perhaps, motorcycle production used up the old welded ones. The early SWB bikes use a smaller battery and a different saddlebag mounting (not all that different from the later-introduced R45 and R65 which were also short wheelbase). Halogen headlamps came later, but the /5 can be converted, most do this with R65 parts, the official factory kit being pricey and no longer available anyway. There is a halogen lamp that will work with the original /5 lens assembly, see http://bmwmotorcycletech.info/lamps.htm.
The /5 had a 4 speed transmission with a kickstart (as well as electric start, common to nearly all BMW bikes after 12/1969). Later in production BMW phased out the kickstart, but kickstart transmissions were available on some models as standard, and on special order or on Euro models, and can be retrofitted or the function added. Many later models are seen with kickstarters, although this is possibly more so with the 'off road' G/S and GS models. As mentioned much earlier in this article, the 1974 kickstart transmissions were weak, and the kickstart on them should not be used except in emergency. The kickstarter shaft on the /5 could move inwards, and a simple fix is available, see http://bmwmotorcycletech.info/transmission.htm.
Many early SWB bikes were converted to LWB (which came in 1973-1/2), and there is often no big reason to do so. Considerations include battery size, stability, saddlebag mounts, if fork mounted windshield. The pre-1981 5 speed transmission can be installed in earlier models. The pre-1981 transmissions had the longer input shaft. Installing a 1981 and later transmission into early bikes requires a change of input shaft, which is pricey; or, machining work. In many instances a pre-1981 transmission fits into a 1981 and later bike, and you need not change the input shaft, just cut it. There are other methods of doing these various things. For example, in some instances, depending on what you want to do, installing a late or early clutch and flywheel (or clutch carrier as it is called from 1981) will enable a particular transmission to be installed.
The 4 speed transmission parts are now very pricey, and few know how to properly overhaul these 4 speed transmissions. I suggest Tom Cutter or Ted Porter or Bob Clement. There is a comprehensive transmission article on this site that covers both the 4 and 5 speed transmissions: http://bmwmotorcycletech.info/transmission.htm
The /5 models came with a 180 watt alternator, adequate for its purpose, but having little reserve for more than an upgrade to the 55 watt H4 headlight and a bit more, such as a heated vest. In 1974, and into 1975, a 280 watt alternator was installed by BMW, and one specific version was such that the 280 watt parts will fit the 180 watt equipped /5 motorcycles, as almost 100% plug and play. After sometime in 1975, the alternator stator parts no longer fit into the /5 timing housing. To install the 280 watt alternator into the /5 bikes, the stator must be 105 mm, not 107 mm. There are a number of aftermarket alternators available, with even more output, two articles covering most of them are on this website.
***At least one true 1976 model (99 mm cylinder bore in the crankcase, for example) has been seen with 105 mm alternator hole, so be cautious here; but that would be very rare.
Expanding the information:
The 180 and early 280 watt interchangeable (physically) alternators both had a 105 mm stator outer diameters, the later ones that cannot be retrofitted to the stock timing chest for those models are all 107 mm. The alternators varied in output over the Airhead production years, with 180 on the /5, 238 on the R90S and 240, 250 or 280 on all the others. The 238 watt R90S had a very slightly changed inside diameter stator, which was done as crankshaft whipping was believed possible on that model and the larger air gap is responsible for the slightly lowered output. Rotor diameters were changed slightly too at times. Alternators over 180 watts use a different diode board, but the later board can be used on the /5 models but not the reverse, except in emergency, where power output would be a bit less. The early rotors were ~7 ohms, and succeeding generations of rotors had even less ohms. Many BMW's had rubber-mounted diode boards which were troublesome and caused charging problems, breakage and aging problems, etc. .........and should be changed to aftermarket solid mounts. There are several article on this website dealing with diode boards, grounding wires, and other allied items.
The battery size, physical and capacity, has changed over the years. There was supposedly a small 9 Amp-hour battery used on the non-electric start G/S, I've never seen one of these. While battery sizes are listed in BMW and other literature on all the other models as 15, 16, 28, and 30 ampere-hours sized ....in truth two sizes cover the fit needed by all the Airheads. Generally those are known as the 20 (or 17) and 28 (or 30). The early SWB /5, and some few other models, cannot be fitted with the standard larger size battery used on other models, as there is no space for the larger battery, although some modifications have been done to accommodate a larger battery.
The 500 cc engine was eliminated in 1973, but a 450 size, the R45, rarely seen and never officially imported and sold in the USA, was produced from 1978 into 1985. The R45 was made in two versions, one had 26 or 27 horsepower, depending on what literature you are looking at, and the other had 35 horsepower. These bikes varied in not only compression ratio but in carburetor size and rear end ratios. There was a definite reason for the differing horsepower/performance ....license classes of expertise for motorcyclists in Germany and elsewhere's had associated changes in vehicle insurance costs and requirements for beginners. Thus, with the proper R45 (see R45N), 'beginners' could legally ride a big bike, but with a lower output engine. For a comprehensive article on rear drive ratios, speedometer ratios, etc., see http://bmwmotorcycletech.info/ringgears.htm.
The 600 cc R60 bikes were eventually eliminated in favor of a 650 cc engine, the R65. The early R65 was on a short wheelbase, something like the /5 SWB models; later R65 models used the larger engine sized frames. An R65LS model was produced with compound construction wheels. The R65 650 cc bikes perform favorably compared to the larger 800 cc R80 bikes. The R45 and R65 are the only boxer Airhead motorcycles that BMW produced from the /5 era onward that use a shorter stroke, compared to the larger engines. These smaller engines are designed, and geared, to run at a somewhat higher rpm. Like all Airheads, the engines are designed to be capable and reliably able to be run for enormous mileages continuously at high speeds and high rpm. The R45 and R65 should not be heavily 'lugged' however ....(such throttle use is bad for any gasoline engine)....because the valves are not as strong.
The R50/5 is not adequate for two-up freeway riding. Neither is the R45N and R45. In fact, they are marginal for freeways without a passenger. The R65 is far better than many think, and will carry two-up on the freeways quite decently.
Pinging (Pinking) on lower graded fuels (even with 91 octane) is a problem with the R50 and R60 models, and can be dealt with. Much of the pinging problem is due to the extremely mild camshaft profile which raises the effective dynamic compression ratio. Often the problem includes excessive carbon deposits in the cylinder head and on the piston.
Airheads came with 18 inch front wheels (R45, R65, ....and many models from 1985); 19 inch front wheels for most all others, although the G/S models had 21 inch. Certain early "cast snowflake" wheels were recalled in the 19" size, and the recall still exists, and the factory will provide labor and a new wheel. Details: http://bmwmotorcycletech.info/19inchrecall.htm
All Airheads had 18" rear wheels, except: some GS, and the R80R and R100R had 17 inch. The various wheels came in different rim width versions, and three styles of internal rim shape; one version in particular was for tubeless tires and had safety humps. BMW also made some very clever spoked GS wheels that had the spokes outside the inner portion, so tube or tubeless type tires could be used. 18, 19, and 21 inch wheels were used on the front.
The Paralever came about in approximately 1987, but all the models were not so fitted; such as the RT. All Paralever bikes are mono (single sided) rear, but not really the same as 'the' Monolever, although there were many similarities.
The Monolever can be swapped relatively easily into a twin shock model.
The /6 began in 1974 with mostly cosmetic changes. The bullet headlight unfortunately went away, but a 5 speed transmission was now fitted. A new size engine was added, the 900cc, as the R90/6. Also added was the famous sporty (S) version, the R90S. It was the only Airhead ever produced that was equipped with Del'orto carburetors. The 1974 into some of 1975 transmissions had problems, as has been extensively noted, well above. In 1976 BMW enlarged the case cylinder hole to 99 mm; previously it had been 97 mm. The pushrod tubes also changed to 18mm. The alternator bore in the case was 107 mm from 1976, although some early 1976 models still had the 105 mm timing chest cavity. In 1975 the front wheel spindle (axle) was increased from 14 mm to 17 mm. As typical with BMW, one can fit things interchangeably if one knows how. ...(one changes the lowers and changes wheel innards).
Production began near the end of 1976 and the 900cc model was abandoned in favor of the new 1000 cc model. An 800 cc model was introduced for the 1978 model year. If the the stock engine has the sloped breather housing opposite the starter motor, and a recessed oil filter cover, then it is a 1977 and later model. The recessed area on the oil filter cover is on the non-oil cooler outer covers, and it is a fairly large round area. The rear of the clamshell air cleaner on the 1977, 1978 R100S, and R100RS, had holes drilled at the factory for better breathing, probably helped with the existing hot air intake too.
The early R65 (and R45) models were SWB, and in the mid-eighties, the larger frame was used, and the R65 always had a very nice thick casting for the top triple clamp ...a handling improvement ...and 18 inch front wheels.
BMW installed tubeless rims and tires on very late models. BMW also designed some clever spoked wheels on the GS, which allowed tubeless tires, as the spokes were located outwards on the rim.
The R65LS was produced from 1982 into late 1985. It had a few things thought of by some enthusiasts as a 'cheapening'. It is not really that bad. They did have compound wheels. Earlier and non-LS models of the R65 were very similar to the larger airheads of the same year, except for the short wheelbase type of subframe (which is somewhat like a /5), and in some few instances some things on the R65 were more desirable (the stiff cast top triple clamp....). The early R65 had a smaller clutch, the later ones (1980 or 1981+) had the same clutch as the larger engine models. The relatively beefy front forks top triple clamp is one of the things that was quite nice about the R65. The R65 also used a different type of instrument pod, which was common to the G/S and ST.
The later bikes basically had two styles of instrument pods, the original /6 type, and the early G/S-ST-R65-R45 type. There were some weird technical things with those R65 instruments, but nothing of great note. Later R65 had the larger frames, as BMW standardized, as I noted. A very differently styled instrument pod was used on the R80R and R100R.
The early 19" front snowflake cast wheels were recalled. The recall is still in effect.
The ignition system was changed in 1979 on all BMW Airhead motorcycles to a canister with a better drive method off the camshaft, and in 1981 that points canister was changed to a Hall device type canister with full electronic ignition. In 1979, and later, BMW changed to a single roller timing chain which is just as good as the prior duplex chain, and possibly a bit better, considering the improved, but not really perfect, guide and tensioning. The points bikes (1970-1980) are reliable, but like all points do require regular maintenance. The 1981 and later ignitions not only have the solid-state (semi-conductor) Hall device, but also have an electronic ignition module located underneath the fuel tank; and for the early years of this change, the module occupied the same place as the prior used cable-driven brake master cylinder that the ATE front brakes with the swinging caliper types had. The electronic ignition bikes must have 5000 ohm spark plug caps, or the system can fail. No BMW airhead bike built from the /5 onward must ever have the spark plug caps lifted while the ignition is on. I am well aware that some owner's booklet may say differently! All models can have coil failures from that abuse, and the 1981 and later models can have the electronics & coil(s) failures from the abuse. BMW used two single output 6 volt coils in series connection on the primary windings on many bikes from the /5 onward, and BMW also introduced a single 12 volt coil with twin outputs, this came on the R80ST and the G/S. Eventually that became standard for the Airheads. Early gray plastic two-tower coils tended to crack and then fail, especially with moisture being present. There is much to know about the ignition, and I have several articles on it.
There can be confusion about the /7 and later bikes. Some feel that after 1976, all the bikes were /7, but this is not so officially, as the /7 production stopped in early 1979, except that some R80/7 were produced into late 1980; & much later for Authorities use. A frame might be identified with a xxx/7 tag at the steering head, yet not really be a /7 motorcycle. This has been a point of controversy and argument for silly reasons. Basically, BMW stopped adding slash numbers, and this confused people.
The fully faired RS and RT models were quite an innovation when they were introduced, and they became the long distance touring bikes of choice. BMW did extensive wind-tunnel testing during the design of these fairings. These faired bikes made a big impact upon the motorcycling world. The RS was introduced in 1976, but few of the earliest ones are around. The RT came in 1979 to the USA. A few aftermarket fairings were available, but one, the Hannigan STe, was very good at slicing through the wind.
For the USA, the early RS and RT bikes had 40 mm carburetors and slightly larger diameter exhaust systems. BMW incorporated, eventually, a dual exhaust crossover, that is, a second crossover, near the transmission, and this was used on both 40 mm and later 32 mm carbureted models. In the final years, a completely different muffler system was used on some models. After the late seventies, all USA-shipped models had a reduction in horsepower, but could be operated on Regular grade gasoline's, but the torque curve remained excellent, so they remain excellent touring bikes.
The highest power output bikes were the R100 series of the late 1970's (somewhat up into 1984 for foreign-shipped bikes). At the end of the seventies BMW began to make changes of various types, including camshaft timing with regards to the crankshaft, exhaust, valve size, carburetor size, and compression ratio, to comply with emissions requirements. Earlier bikes need premium fuel, later bikes can usually use regular grade. There is a lot to know about various valves area problems, an extensive article is on this site: http://bmwmotorcycletech.info/valves.htm
~1987 and later bikes, for almost all countries, including U.K. and USA, had the reduction in horsepower (about 6 or 7 hp less on the higher output RS and RT models, less change on others), but the torque output remained nearly the same.
The rear disc brake with Maguro-built master cylinder was introduced on the R100RS in 1978, and it had a Brembo caliper. It was introduced on , the R100S and R100RT in 1979. The Brembo front caliper(s) and the Magura on-bar master cylinder came about in 1981 for all Airheads. Prior to using Brembo front brakes, the front brakes were either the swinging type made by ATE, which had an under-fuel-tank master cylinder; or, were ATE single spot calipers that were fixed, and looked something like the Brembo's. Every Airhead that came with single disc brakes can be converted to dual-discs. There is a fair amount to know, so refer to http://bmwmotorcycletech.info/brakes.htm. After 1981 linings were non-asbestos. Squealing of brakes is fairly common, and the brakes article discusses this and how to fix it. In my opinion the rear disc brake does not have the stopping power of the rear drum brake, and the rear disc brake was included for marketing purposes. The rear disc brake was discontinued later, and replaced by a brake drum. In the early eighties, the rear drum brake had narrower shoes, and some other things were changed such as the O-rings, etc., on the brake actuating shaft. All is described in the above brakes article.
BMW stopped production and importing of the R100RT for the USA for a period of time between 1984 and 1986). Initially, and simply-put here, BMW sold and imported into the USA a supposedly last model series known as the "Last Edition"; and then, due to screaming by enthusiasts, re-started production for the USA. It was a messy situation for everyone. During this period, which is a bit complicated with models, etc, these were not officially produced for the public (some police models, known as Authorities types in BMW literature were produced). BMW tried to placate those who had sometimes paid a premium price for Last Editions, by offering free helmets. It all became somewhat of a public relations mini-nightmare between BMW and die-hard BMW traditionalist owners. This so-called Last Edition has nothing to do with any similarly named bikes in the mid-nineties.
The R100 cylinders won't fit the R90 cylinder heads.If you contemplate making piston/cylinder/head types of changes, see:
Between 1979 and 1980 the swing arm housing size got larger, and the driveshaft design was changed to a driveshaft with the torsional stress relieving spring and cams, often called a cush driveshaft. In general, parts will interchange with or without minor work.
Fitting of oversize tires on the early bikes can be a minor problem. The front fork brace on some models might need to be replaced with a later version. For the rear, particularly if prior to 1981, you may need one spacer changed, not expensive and very easy to change; and BMW sells the wider spacer. Still, some 120 size tires of some manufacturer's will not fit properly. Oversize tires change handling, not necessarily for the better ....and the removal of the rear tire may be more of problem if you get a flat tire ...if you have tube type tires. Most 110 x 18 tires fit fine with the spacer change, but some 120 x 18 are too wide. For the later twin-shock years, a minor modification on the rear disc brake stay, and adding a left side washer spacer, and using the wider right side BMW spacer, will allow most all 120-18 road tires to fit OK. After approximately 2010, more tire manufacturers began to produce original inch size tires that fit both rear and front, and with new rubber and tread designs, even radial tires are being produced. These are proving to be very good. Most all of these newer...and many of the older...tires.... are gotten into, in depth, with testing, in one article on this website: http://bmwmotorcycletech.info/section5.htm
The front forks were changed fairly radically internally in 1981, to a worse fork. At the same time the rear drive housing casting was changed, side-stand modified, the master cylinder was now a Maguro type located on the right handlebar. That was a good change, eliminating the often leaky, hard to bleed, and slightly spongy operation of the cable-driven master cylinder under the fuel tank that was used with the ATE swinging caliper style of front brakes. In place of where the under-tank master cylinder was located, was now installed the heatsink mounting for the electronic ignition module (module needs to be removed & heat sink paste renewed every couple of years). The heat sink was moved to the right side of the frame backbone later, and still needed the heat sink paste renewed now and then. The very last version of the electronic ignition module used a permanently riveted module/heatsink, that does not require heat sink paste renewal.
The first disc brake was introduced with the R75/6 and R90/6, the R90S getting dual front discs. ATE swinging calipers were on the early bikes, and they take more effort to adjust properly, and more work to bleed of air bubbles, particularly at the under-tank master cylinder; while the Brembo brakes and later ATE non-swinging brakes have no adjustments at the caliper area. It is possible to improve braking by various means. Earliest brakes on the front wheels were drums, and they are fine, except that they can grab on a damp morning for the first stop, and will fade under severe use. A single disc brake is not always more powerful in initial braking than a properly set up drum brake. That applies to both front and rear. BMW front drum brakes, used only on the earliest Airheads, are of the twin leading shoe type. Properly set-up, they can work quite well. "Set-up" is not just the external adjustments.
Brembo front disc brakes replaced the earlier ATE swinging type. The ATE 'swinging caliper' brakes can be OK, but one needs to know how to adjust the eccentrics and bleed the system, etc, and they still are not as good as the Brembo's. There may still be an article on the Club website, www.airheads.org, about that. I have a brakes article too, link at the end of this paragraph. It should be noted that every model with a single front disc can be converted to a dual-disc. BMW offered slightly thinner discs on some models, particularly with dual front discs. I think they were trying to keep good handling by keeping the weight down; resaid, BMW put a single disc on the ST and GS models to help front end handling. Also, as noted well above, ATE did make a type of brake caliper that is similar to the Brembo, it is not the ATE 'swinging adjustment' type, and looks much like the Brembo, except for ATE cast into the outer area, and its color, until you compare more closely. The 1979 R65 was one of these. These are excellent brakes. A 1979 R65 bike converted to twin front discs with this ATE non-swinging caliper and proper master cylinder piston size (original works fine too) can stop very well; you will think you almost have 4-spot brakes. When converting from one to two discs, one may want to keep the original single brake disc master cylinder size ...that usually works out quite well. http://bmwmotorcycletech.info/brakes.htm has everything, just about, regarding brakes, and various modifications.
In the U.S. models from 1980, the compression ratio was lowered, to allow lower octane fuels and as part of the coming unleaded fuel changes. It is possible to raise the compression ratio with different BMW pistons, or to mill the head, or even turn the cylinder base. If one mills the head, one must also do something about the recess area of the head that the cylinder lip fits into. It is relatively easy to modify head or cylinder or both, depending on the situation. Several folks on the Airlist will do this type of work properly. Be sure to get someone with considerable experience and knowledge. Milling is usually done at the time the heads are converted to dual-plugs and/or piston change for higher CR ...all of which are of some advantage for fuel mileage, ease of starting, the dual plugging itself (without CR increase) lowers octane requirements, etc. Going to different intake spigots and carburetors (from 32 mm to 40 mm) can further improve power. Going to the larger cylinder head valves is of lesser help, but does increase power somewhat, as does the stock larger exhaust system.
1981 brought about major changes, some of which are already noted herein. Electronic ignition, Nikasil/Galnikal cylinders, heads modified, major changes to the clutch/flywheel, changes to the transmission, frame beefed-up, ETC. In 1981, the simplified newly introduced front forks were noisy (some modifications, at intervals, came soon), and I think they did not work as well as earlier forks. The forks were modified some several more times. The 1981 frame was not exactly the same as the 1982 and later twin-shock models ....and the 1981 and somewhat later years to 1984 were particularly hard to put on the center-stand ....a kit is, or was, available. The 1980-1981 clutch/flywheel ('clutch carrier') was not overly strong and some of them blew up, and could damage the transmission input shaft at the same time; this was fixed in 1982. The transmission on the 1981 were having neutral and over-shifting problems due to the lighter clutch assembly reducing inertia in moving parts during shifting, and BMW began phasing in the so-called Shift Kit, which should have been completed by late 1982. Whenever BMW introduced radical changes, it seems there were bugs in them, witness the 1974 and the 1981 bikes. Oak told me that some 1981 castings for engines or transmissions had incorrect dimensions, which could cause perpetual failures of the input shaft of the transmission. There is no fix for that, I think. I personally have never seen this, but I trust Oak's information.
From late 1980 to 1984, the type of valve seat material was changed, and gave serious problems, especially on the hotter-running R100 engine models. Prior to 1981 models, using unleaded fuels was bad for the valves and seats. 1981-1984 bikes had a serious problem with the valve seats in the cylinder heads that caused valve overheating. There is an article on the valves/valve seats on this website, detailing it in great depth, a must read! BMW had serious exhaust valve problems with use of unleaded gasoline's for the early models prior to 1981, and from the valve seats from 1981-1984 ...until 1985 when they made a final fix for the valve seats. Note that the full final fix for the valves/seats problems was supposedly done for the 1985 models, but some 1985 and 1986 have been seen in which the changes were not done by the factory. All the valves and seats problems have been discussed in depth, many times, in AIRMAIL, the monthly publication of the Airheads Beemer Club, and I have done an article that is posted at http://www.airheads.org. This is worthwhile reading but the information is considerably expanded on the website you are presently reading, at http://bmwmotorcycletech.info/valves.htm; where you are advised to get all the information. That and my transmission articles are must reads.
Some gears in the transmission were changed, from a 15° angle to 17.5°. You can't, in overhauling a transmission, mix 15° and 17.5° parts, but a transmission can be converted. I fail to see any reason to do that ...unless ...one is changing to an aftermarket higher ratio 5th gear ...a long messy story, that. If you have a 1974 transmission with serious problems, you may be forced to upgrade ...see prior information on this page. The http://bmwmotorcycletech.info/transmission.htm article is very much more extensive in describing all these things.
There are rumors that the later model's crankshafts were designed and balanced for the R80 engine, and is therefore not as smooth on a R100 engine. This rumor can be discounted. What is true is that when the R100 appeared, the pistons were very carefully designed to maintain the desired original balance weight. It is also true, for more than one reason, that the R80 engines tend to be very smooth. It is also true that some R80 and a few R100 engines were made in the later eighties that badly vibrated, and there is no good fix, although careful balancing and shimming the crankshaft will help considerably.
The Airheads, part 3:
While it is possible to fit almost all the latest model Airhead valve gear to most earlier models, with less convertibility on the /5, you might like to see some photos and descriptions of the various gear. I suggest: http://www.largiader.com/tech/rockers.
If the flywheel is removed, the rear face of the engine is then exposed, and you can see casting information stamped (cast-into) the area. Typically there is a two digit number signifying the year of manufacture; and that number is surrounded by 1 to 12 raised dots which signify the production month of the casting.
Some engine blocks for replacement purposes were made without any serial number of the type at the dipstick area as normally seen on the pre-1984 models. The dealer was supposed to transfer (stamp into the metal) the old engine's number, and destroy the old engine and/or ship it to BMW (or Butler and Smith ...which was the importer/distributor before BMWNA). Some dealers did not apparently have metal punches and there may be no stamped serial numbers on those replacement engines. Note that 1984 and later engines did not come with serial numbers at the dipstick area; and, in fact, the engine block serial number is nothing like the earlier models, and you should refer to the id numbers article for information in depth: http://bmwmotorcycletech.info/IDnumbrs.htm
1977++ (and a few in 1976):
Valve covers can not (well, should not) be reversed anymore; or the fins don't look right. The first full year, 1977, of these new valve covers had left and right sides identified internally. Alloy pushrods with steel ends quiet the valves a bit, fit the area for them better, and make clearances a bit more constant with engine heating; crankcase is made stronger; cast-in breather housing area; deeper sump...changed again in 1981. Most of the cylinders, and eventually phased into all production, now had a large O-ring at the base (the cylinder base now had a machined groove) to ensure positive sealing to the engine, hopefully to prevent oil weeping and one does not have to use a sealant like Hylomar. Hylomar is no longer recommended by me for this particular purpose. I have an extensive article on sealants, chemicals, cleaners, waxes.....etc:
Instruments still had white numbers, but red needles. The area below the steering head is strengthened; RS is introduced and gets a larger diameter exhaust pipe system and 40 mm Bing CV carburetors. The cast wheels called Snowflakes are introduced.
The 19 inch cast front wheel only, of production before 10/82, have all been recalled...see: http://bmwmotorcycletech.info/19inchrecall.htm
1978: linkage type gear shift lever arrangement introduced; electronic tachometer; R80 engine; RS with Brembo rear disc brake (and both RS and RT from 1979). Valve Covers have L & R information on the outside. In ~mid-1978 BMW begain installing a larger 2-bulb tail light assembly. The wiring was no longer in the frame tubing but alongside the tubing.
In 1977-1978 the piston pins clips changed from internal to external type. Not all 1978 had this change. Some had the pistons re-machined.
1979: Points in a canister; single roller timing chain with hydraulic tensioner; spring/cam shock absorber system added to the driveshaft. RT introduced.
1980: Lowered compression ratio to the U.S.; modified oiling system routing onside the engine; rectangular air-cleaner (two types, depending on Country); pulse air system (not all countries); 85 mph speedometer (U.S.A.); single throttle cable at throttle and same for choke, which is located at the left bar. BMW began to put various numbers and letters on a raised flat boss of the crankcase, located below the left cylinder, slightly forward. Interpreting those characters is in another article on this website: http://bmwmotorcycletech.info/IDnumbrs.htm
1981: The old heavier clutch/flywheel assembly eliminated in favor of lighter 'clutch carrier' styles; this necessitated shortening the input shaft on the transmission. 1981 also brought electronic ignition; a larger sump; a modified clutch lever at rear of transmission; brazed-on pushrod tube collars; and Nikasil cylinders (a big improvement!). Engines vibrate more...generally....and are more touchy to get smooth with carburetor adjustments...due to the lighter clutch components. Shifting problems due to the lighter assembly were begun to be fixed in 1981, and BMW had the shift kits fully phased-in by late 1982. The 1981 and later CS (Classic Sport) models were supposed to have wire wheels, but they had interference problems with the Brembo brakes in hard cornering, so snowflake cast wheels were installed at the BMW warehouse in the USA. I think that no wire spoke wheels on these ever got sold to the public. It is possible to install wire wheels, with correct changes. The 19 inch cast front wheel only, of production before 10/82, have all been recalled...see:
1985: Service as necessary by replacement, not cleaning and greasing, became standard for new style front wheel bearings. The valve gear was modified, and were quieter, but the rockers are not as wide; there is a plastic spacer and the end clearance of the rocker arms is now set by shims.
Some of 1984 to end of 1995 production, any and all Airheads: BMW abandoned the use of a part (circlip) in the transmission next to 5th gear, and made a few other associated changes. A considerable number of transmissions have failed due to this. http://bmwmotorcycletech.info/transmission.htm
Noise or vibrating in operation or feelable (sharp bits) metallic particles at the transmission magnetic center drain plug are all cause for investigation. Other tests are appropriate, some should be repeated often. Note that some of the similar sort of vibrating symptoms can be the Paralever bearings and U-joints. The transmissions can be updated (de-dated?) relatively easily once they are taken apart. If one has sudden unusual vibration in the transmission or drivetrain in general >>>stop riding now ....no more miles ....not any!!!!
The Airheads, part 4 ......Last of the Airheads:
Some models were produced into the 1990's. Versions of both the R80GS and R100GS; plus R65, R80, R80RT, R100RS, R100RT. A version of the R100RT called the Classic was built as late as September of 1995, and maybe 1996 for the EURO civilian market, and I think some R80RT and R100RT were built as Authorities bikes into 1996. Some bikes, such as the R80R and certain GS versions, were not imported by BMW into the USA. The R100R bikes all had the latest fixes, of which there were not many ...but: R100R transmissions might not have the circlip, the usual expensive problem if the transmission fails. I recommend you read this long article: http://bmwmotorcycletech.info/transmission.htm
More on the R80R, R100R, R100M ....and even a Classic version...:
New models, the R80R and R100R (and versions sometimes called the Classic, and also the R100M called the Mystic) were produced between 1991 and 1995. The first years (1991-1992) had single disc front brakes, thereafter the brakes, which are very good, were dual-disc, 4 pot Brembo's. AFAIK, only a few hundred of the R100R bikes came to the USA. There were quite a few changes, some subtle (such as rear shock length, which reduced the U-joint angles). In some ways, these Paralever bikes with Showa forks were the best handling Airheads. They are rather similar in many ways, except for the Retro-styling and equipment, instruments, etc., as on the R100GS, and a special dash version too. One might simplify things by saying the R bike was a R100GS with a K75 front end, although that really is an over-simplification. The exhaust system was different from earlier Airheads & the instruments-group styling is a matter of one's personal taste; there were two versions of them. The saddlebags were like the Tour Bags on the K bike models. Those shipped to the USA had the 32 mm carbureted motors. Changing to the Euro spigots & 40 mm carbs; and changing to higher compression pistons, and some head and valve work will seriously improve acceleration and top speed ....this could also be said about all the 32 mm carbureted R100 engines, from the early eighties.
Bottom line, is that except for the possibility of the transmission circlip problem, these were, arguably, the best Airheads, as far as over-all handling goes, & possibly had the least problems. Styling was a matter of taste.
BMW made some models seldom seen in the USA. The R45 and R45N are quite rare in the USA. R65GS is very rare. There were Police (Authorities) models of many Airheads; an example of which is the R100TIC. This was sort-of a naked R100 that had a low compression engine of 67 HP, but the RT fairing was added, with police equipment as ordered. This was a Euro-available bike only. Since it was not a RS or RT, it came with a rear drum brake. It was primarily made from about 1980-1984. A full treatment of all the special BMW models is far beyond what I can or should do in this article. If you cannot find, elsewhere's, the information on a specific model, you may furnish me the full VIN or serial number, and all information you have, and I can possibly identify the bike and details. Your BMW dealership or Independent 'could' also do that for you.
The Airheads, part 5, weights, etc:
The weights shown in various literature about BMW motorcycles are often wrong, sometimes wildly wrong. Some of the differences come from failure of you or the literature editors to understand BMW's own literature; some differences come from translations or conversions. Differences also are due to models as shipped to various countries. Some were available without starter motors, and different sizes/weights of batteries, different oil pans and fuel tanks were sometimes installed by the factory. BMW's weight figures include full fuel & oil & standard tools. BMW's full fuel capacity figures are with a full tank of fuel, whether or not your can fill it that full or not, as some tanks are difficult to fill that much, on purpose, due to flapper valves, etc. Non-stock shock absorbers, different saddlebags, or adding racks, backrests, etc., make for small changes.
In general, the figures I have, below, are for standard USA models (unless otherwise identified), standard equipment, full fuel on standard tank (at capacity on U.S. gallons), & with oil and tools as appropriate to that model. There are some anomalies, in which dead-stock bikes were actually measured, and did not agree with published figures. As one example, the R90S, officially 474 pounds wet, but was measured at 452 dry (no oil, no fuel). The fuel alone weighs more than the difference.
Model or Item
|R50/5; R65; R45;||452|
|R80G/S||423||With electric starter, std. battery|
|R80ST||436||No kickstarter, 1984|
|R60/5; R60/6; R75/5; R75/6/; R80; R90/6.||463|
|R60/7; R75/7; R80/7; R90S; R100/7; R100T |
|474||R90S, measured 452 dry. R80, measured 463 dry. Others without fuel, without tools, but with lubricants: 430 lbs.|
|R100S, R100CS||485||Without tools and fuel 441.|
|R100RS||505 to 507||Measured 463 no fuel, for 1978-1979 USA models, but with lubricants.|
|R100RT||516 to 525||Depending on year. 6.3 gallon (24L) tank is assumed. Includes all lubricants and full fuel tank. Without fuel, 472 lbs.|
|R80GS PD; R100GS PD||1988-|
|R80GS PD; R100GS PD||1991+||520||Tested at 588 with full tank|
|/6 transmission||24||Drained; without shift lever|
|R65 LS rear drive||1982||16||Drained; with brake shoes|
|Engine, R80/7||1978||140||With starter, with carburetors, without ignition coils, without intake system.|
|Engine, R100/7, S/RS, RT||1979||138||As above|
Gasoline weighs ~6.0 lbs per USA gallon.
Lubricating oil weighs ~7.5 lbs per USA Gallon.
Most early engines had 2.38 quarts of oil (0.6 gallon) (including the oil in the oil filter).
Later engines had 2.64 quart, and later with the cooler had 2.91 quarts.
Transmissions had 0.85 quart.
Rear drives had 0.26 quart on early models, later ones 0.37 quart on all models except the R80R and R100R had 0.28 quart.
Early driveshafts had 0.11 quart of oil, after which they had 0.16 quart (except for the dry shaft Paralever models).
The front forks varied considerably. For early models you can assume ~9-1/2 ounces per each of the two legs; the GS models had up to 17 ounces per each of the two legs, and the R80R and R100R models had 14 ounces per each of the two legs. Because of extensive confusion on this subject, and recommendation changes by BMW, information is in its own article in a chart on this website:
The /5 series fuel tanks held either 5.39 or 6.34 gallons. Except for the models listed just below, most tanks held 6.34 USA Gallons. That capacity was not necessarily what you could, or not easily, fill the tank to, because later tanks had flapper valves (many owners removed them), and if filled to the flush-filler area, held 6.34 gallons. Note that BMW fuel tank specification includes the reserve, and the capacity is to full (whether or not you can fill it that much). Some tanks vary a small amount in ways you might not think of, including the space for the ATE under tank master cylinder; and, BMW was not careful about specifying the difference in capacity between the early flip type caps and the later tanks with the screw-in removable caps....which either had a flapper valve (or not); but the neck, if not well-filled, detracted considerably from the fuel capacity. The actual reserve amount (included in the tank capacity) varied, and the left and right sides were not quite the same capacity, a cup to three cups difference.
The R80ST and R80GS had small tanks of 5 gallons plus ~ a couple of cups. The RS & RT models generally held 5.55 gallons, although some held about 5.2 or 5.3 gallons. The PD models had large tanks with the R80GS PD holding nearly 8-1/2 gallons (a non-imported version had 26 Liters). A larger GS-PD tank was available, and sold with many of the bikes as standard, and it held 9-1/4th gallons.
© Copyright 2018, R. Fleischer
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Last check/edit: Friday, May 18, 2018