Airhead model differences over the years
(PLUS information to identify the model/year, if you do not have a serial number, ETC.)
©Copyright, 2013, R. Fleischer
Before getting into the differences between models and years, let me clear up something about "identifying year of production by serial and/or VIN number". Beginning in 1980, U.S.A.-shipped bikes changed from a pure serial number to a Vehicle Identification Number. This new type of 'number' is a combination of numerals and alphabet and the total length is always 17 characters. The TENTH position character (from the left beginning) is the official production year. As an example, for 1980, that was an "A". Each year following was one letter further in the alphabet. NOTE that 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 case, the last SEVEN NUMBERS will fully identify the year and model....IF......you have the BMW factory or other charts information. ALL BMW vehicles, and ALL other brands of vehicles, use the same 17 character VIN NUMBERING SYSTEM. NOTE that actual year model production could have been at the end of the PRIOR year, due to the Company vacation and restart of production after that vacation. That means September. There are exceptions and anomalies...so:
For VERY considerably more information on VIN and Serial numbers, sequencing, etc. see the following article: BMW motorcycle ENGINE AND FRAME NUMBERS
"Airheads", for the purpose of this website, and this article, are taken here to mean the BMW boxer-layout engine with two valves in each head, as produced beginning 12/1969 as the /5 models...and Airheads are generally considered as being in production until 1995.
In no way can the details in this article be considered to list every yearly change. I will list the more important changes here.
Models PRIOR to 1970:
This article you are reading has a small amount of information on
models prior to the /5...to set some background. A detailed
discussion of the various models prior to the /5, is NOT included
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 that paid the bills. For a
discussion of of these early bikes, refer to:
3. http://www.benchmarkworks.com/....A source for technical information, parts, ETC. for early BMW's. There are few knowledgeable folks that specialize in working on or supplying parts and information for earlier than December 1969 BMW's. This one in particular is Bench Mark Works, Craig Vechorik ('Vetch'), 3400 Earles Fork Road, Sturgis, MS, 39769 USA, (662) 465-6444
There are websites and groups devoted to the early bikes.
I can supply information that is in the above sources, and more. Check with them first...I am busy enough!
/5, /2, G/S, ST owners....and some
others....have their own websites. See MY
BUT: The MAIN source of information for all BMW AIRHEAD boxer models made from 12/1969 are NOT the single model websites, but the Airheads LIST. See the Technical Articles List page for information on how to get on the Airheads LIST. It is free.
BMW has tended to find ways to use up old parts bins stocks, and has shipped various combinations of components. It is fairly easy to swap many of the parts used on MANY OR ALL Airheads. While there is a lot of interchangeability possible on parts and components, this is NOT to be taken that all can be interchanged. There are very specific problems in interchanging MANY items. It is also possible to put some items from other BMW bike lines into Airheads. The K bike front ends and brakes, for example. 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, and information on other things, like drive-shafts, rear drives, fuel tanks and seats, etc., are found scattered in the appropriate areas on this website.
NOT all models were shipped to
the U.S., in any given year. In fact, BMW stopped shipping
R100-engined bikes for a couple of years in the 1980's; and the
R45 bikes were never imported into the USA by BMW.
Here is a
good website page, showing a chronological index for BMW
motorcycles. If you click on a model, you get a lot more
The MEAT of this article starts here:
There have been MANY changes to the Airheads over the years, yet a lot of similarities. This article is NOT to be considered as showing all the changes....there are too many. Cosmetics are generally not included here.
In late 1969 BMW began the /5 series. The /5 was a
radical departure from their previous motorcycles. Although
BMW had conventional telescopic AND 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 being
used. I do NOT consider the new rear sub-frame as an improvement. As
the years rolled on, BMW did beef up the frame, but the separate
rear subframe was always a problem ON THOSE MODELS USING IT.
It contributed to the famous 'rubber cow' effect.
The swing arm type of rear end, incorporated a bit earlier, was retained, and the much older plunger design abandoned. The engine had a considerable amount of change. Mechanically, the biggest change was to move the camshaft location to below the cylinders, this improved oiling, the pushrod tubes delivering the oil from the top ends to the camshaft lobes by draining downward inside the pushrod tubes. The engine internal oiling system was much modified. An oil filter was incorporated, where only crankshaft 'slingers' were used before. This eliminated the need to remove the crankshaft every 30,000 miles (or so) for slinger cleaning. 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. If you have a /2, you CAN install a 12 volt alternator and lamps conversion, and even coil ignition can be installed (not needed IMHO), and using the best modern (especially synthetic) oils can extend the time between crankshaft slinger cleanings, although just how much is questionable, and depends on engine condition. For instance, a worn engine allows more blowby, more contaminants into the oil, 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.
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 beefy larger diameter axles and frames that flexed much less...all of this was because they were DESIGNED 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 use of the separate rear frame causes minor problems when fitting a sidecar to a /5 and later Airhead. The earliest Airheads, like the /5, had a thinner front axle diameter than later Airheads; and some bending had been seen under severe conditions, hence the factory change from 14 to 17 mm. The /2 era bikes steering heads had ball bearings, which were NOT as good as the /5 and later tapered bearings. Luckily, /2 era steering head bearings can be relatively easily changed to the later tapered roller bearing design. Higher capacity alternator conversions are available, as well as many other items for the Airheads....and some for the /2 era bikes too.
The /2 series ended the use of the very nice looking early type turn signal housings.
The first /5 models had a shorter wheelbase (easily seen by a
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 the early R65 (also short
wheel base) could (not WILL), have some potential for instability
under SOME SPECIFIC types of riding....and IN PARTICULAR if a
STEERING mounted windscreen was installed and there was
considerable weight aft of the rear axle and speed was high. BMW elected to go to the LWB (Long Wheel
Base). You can see the welded-in
section, used for many years after it became standard.
The R65 continued the SWB for some time.
The LWB also allowed for a bigger battery. Frankly, my personal preference is the SWB. It feels quicker-handling. BMW incorporated the longer wheelbase in mid-1973 and had a later addition of a cushioned driveshaft. The cushion was provided by smooth cam action backed up by a strong spring.
/5 bikes had 10 mm flywheel bolts, and the 1974 /6 also
did...these could be twisted off from rider abuse during riding.
slightly later /6 may have them...perhaps into early 1975.
After this, the bolts were 11 mm.
In identifying a /5 engine block, there is an eyebrow cutout on the front face of the engine block and it is solid from 1974. See:
Obviously, this is not easily seen on a motorcycle that has the timing chest and outer cover still on the engine!
NOTE that the /5 SWB bikes and LWB bikes use different saddlebag mounts. NOTE that the early R65 can be fitted with its own bag mounts, or /5 mounts adapted.
The /5 came with a 45/40 watt NON-halogen headlight. It is best to convert to an H4, BMW offered a kit for that. You HAVE TO change the lens too, OR the H4 pattern is spread about and awful. You can rather 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. Modification of early chrome rings to avoid loosing the ring, headlight, etc., is a good idea.
Other changes later on (mostly from
1979, some earlier) included disc brakes on various models, some (RS
and RT) had them on the rear as well as the front. Having a
rear disc brake is probably only a sales item, as the disc brake
is certainly no better than the drum brake...which BMW went back
to, years later.
The /5 models came with a crankshaft rear mainseal that tended to leak after enough mileage, and maybe dirty oil helped that along. BMW has made a LOT of changes over the years, and the chances are small that you will find a /5 or even and early /6, with the original type of WHITE seal. With the /6, BMW added an O-ring inside the flywheel bore, and with the /7 came a metal cap and the same O-ring continued.
The 1974 was a not-so-good year.
NOTE here that when I say 1974, that MAY include into
early or even mid-1975 calendar year. The newly
introduced /6 bike had
carry-overs from the /5, and new problems. The 1974
STILL had the 10 mm flywheel bolts; shearing them off could ruin
a crankshaft, sometimes just messed up the threads a bit. The transmission was the
first 5 speed
and had many problems. The Pawl springs would break,
the kickstarter parts were soft and wore (don't use the kickstart
on a 1974 unmodified transmission unless actually needed). The input
kickstart gear was soft, and wears considerably. The shift forks were too wide,
and gear dogs broke. You can't purchase the gear alone, only the
whole cluster assembly...and THAT original one is no longer available.
That means that you have to install the 17.5° late model items, and that is
$$$. There is a huge amount more on
transmissions in my
article. Finding neutral was often difficult, and overshifts also
happened.....and the problems were not mostly
fixed until 1976. As I mentioned, some 1974 transmission parts are
now NLA, and 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 from and including the /5 to 1980. The handlebar
controls of the 1974 were a carryover of sorts from the
/5. Some of these parts were part /5 and part /6, 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). Under some severe usage, the front axle could
bend. You CAN make simple changes in the wheels to accommodate the later
fork lowers and 17 mm axle. The 1974, ONLY, had
"strange" fork tubes/lowers (1974
lowers are NLA). Engines tended to vibrate around 4000-4600
rpm. The frames were a bit weak, with the 1975 being
better, and the 1977 better yet, with more substantial bracing. The
1976 incorporated many upgrades, including the larger pushrod tubes, pushrod
changes, engine case cylinder hole size increase (later engine's Nikasil
cylinders will fit).
BMW made their "Hot-Rod" the R90S starting with production at the very end of 1973, for model year 1974. Production ceased in mid 1976. The bike was the only one 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 is a cult collectors item. The very first models were the fanciest looking. The R90S had a high compression ratio engine of 9.5:1. Performance was at least as good as the Euro version of the later R100S/R100RS/R100RT.
During production time of the R90S, the factory began deleting things. Fewer chrome fasteners, chrom 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 improvements along the way too, 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 BMW also finally installed the electronic tachometer that had already been wired-for in the bike. 1977 bikes had good horsepower output, good torque.
1978: The transmissions had gusset reinforcement running ONLY from front to rear (NONE left-right).
in 79 the gusset reinforcements at the bottom of the case were cross hatch like
a crossword puzzle.
In 1979 a different system of
driving the ignition points came...the "canister".
That canister contained points for just the 1979 and 1980
years, and worked well. 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 canisters), and engine timing
setting...all easy to do. Stock system points last about 15,000 to
20,000 miles, then must be replaced.
amplifiers or boosters are available that reduce the current
through the points, and I recommend them. If the points are
installed carefully, and kept LIGHTLY lubricated at the felt pad
and points cam, then with a booster or amplifier, the points life CAN TRIPLE
OR MORE, yet be EASILY field-repairable
in a few minutes, if the
booster-amplifier should fail. The 1981+ electronic
ignition is quite reliable, very powerful too...but for reliability
you must NOT pull off the spark plug caps whilst running
(BAD idea for ANY 1970+
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
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 had such a single,
dual output coil, but the later ones are more
reliable. Some early models in the 1980's had two
separate 6 volt coils in series, which were very reliable.
You can read all about the
ignition stuff on this
website. Besides that link, there are articles on
dual-plugging, single plug ignition, ignition theory.
From 1980, BMW made a change in the oiling system that is cast into the block. see: oilsketch.htm
It is not anything critical at all. 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 was needed. Then 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.
A fairly radical change was made to the clutch in 1981,
together with the vastly 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'. Anyone
with an original 1981 clutch being worked on, should update to the later
parts. There is an extensive
clutch article on this
Note that pre-1981 and 1981+ transmissions are different on input shaft lengths, so take this into account if substituting transmissions. Shafts can be changed at $$$ cost, 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, by another company also making these cylinders: Galnikal) is a special coating in the cylinders. That coating wears very slowly. The cylinders could now be made of all-aluminum, the older iron sleeves eliminated. Cooling was improved, and the new cylinders last almost forever, and oil burning is reduced, compression stays higher over time; and every aspect of roundness, taper, etc., is IMproved. The new 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 references 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, all sorts of pistons are available, and they can be bored conventionally,,,,preferably by someone who KNOWS BMW airhead cylinders!...boring can be very tricky to do correctly on the iron cylinders.
In 1983-84 (1982 in Europe) an R80ST model was produced with a single
sided rear end 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 ones are VASTLY 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 disadvantages are that when that bearing
does wear, it is more costly to replace. Another disadvantage is that a
twin-shock rear end is theoretically better suited for use with a
sidecar. Many a Monoshock or Paralever bike is
pulling a sidecar, however.
A FEW Monolever rear drives were, perhaps, not produced correctly, and failed early.
Fully faired models were produced from approximately
1976. The R100RT was first, and made quite a splash in the
U.S. in 1979. In 1987 a Paralever model was
introduced. The introduction was on the R80GS and R100GS models. The
Paralever was supposed to be an improvement on the Monolever,
adding a link
to the rear drive, coming forward, that eliminated the jacking effect of the
rear drive. For the most part, any jacking was not really too detrimental during even
fairly hard riding, but the magazine press disliked it, always
having previously faulted or looked down upon the reliable BMW
shaft drive bikes with the jacking effect. The Paralever driveshaft
bearings and U-joint are not nearly so long lasting as the
lasting-nearly-forever prior versions.
This is particularly
so on the GS models, which have quite an acute angle on the
system. Shaft failure problems of the GS, especially the
R100GS, have not ever been fully solved...although work on that by
private folks was done in the early 2000+ era...but worked
stopped due to lack of funding. Various 'fixes' for
the GS driveshaft are available, none seem 100% perfect, but all probably help with
longevity; information is in the references pages on this website. Two
reference pages for this website are:
There are fixes that involve rebuilding the
driveshaft U-joints; fixes that eliminate the sometimes
troublesome CUSH RUBBER section (which can get the driveshaft
ends out of perfect synch), fixes that add grease fittings with a
different U-joint, and so on.
The Paralever bearings can be 'upgraded' (market hype!) with an aftermarket solid bearing that is quite sturdy; yet it is not really an improvement, and CAN create new problems!! I do NOT recommend them.
The Airhead Paralever bikes occasionally have rear drive troubles. Opinions differ on why and how these troubles come about. Opinions are such as: (1) improper shimming of the crown gear; (2) use of overly high viscosity oils; (3) both 1 and 2.
Last of the Airheads: Some models were produced into the 1990's. R80GS, R80, R80RT, R100RS, R100RT (to 1994), R100RT Classic. A new model, the R100R model, was produced in three versions, R100R, R100R Mystic, and R100R Classic, and produced between 1992 and 1996. There was also a R100RT Classic produced in 1995-1996 that was never imported.
Some of these various bikes, besides as noted
above, were NOT imported by BMW into the USA. These R100R bikes all had
the latest fixes, of which there were not many...BUT: The transmissions,
at least prior to 1995 (see transmission article) might not have the circlip, an
expensive problem if the transmission fails. I recommend you read this
More on these R100R models, much further below.
BMW airheads have NOMINAL displacement, with the actual displacement being slightly lower than the number indicates.
The /5 bikes were produced as R50 (500cc); R60 (600cc) and R75
BMW has produced various single cylinder displacement models.
Other BMW twins including the 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 1996 had two opposed cylinders. The cylinders are NOT directly opposite, but offset slightly, as the rods are side-by-side.
The /5 bikes had the classic bullet headlight and instrument shell and used the infamous 'stick' ignition key, one size fit all. Restating this, after the /5, the FAMOUS 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 speedometer/tachometer unit in the /5 is a fun and games job of removing for service.
The /5 had a starter relay, mounted under the tank, that was
specially designed and wired to prevent the starter being energized and 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 much detail, slash5cricket.htm
Later models 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 /3 and /4 or before, had many troubles. There is an article devoted to those early carburetors, on this website.
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 never figure out how to duplicate (unless you also have a steering mounted fairing and maybe some rear area weight), some 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. The early SWB bikes use a small battery and a different saddlebag mounting (not all that different from the earliest 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 /5 lens assembly, see my LAMPS article.
The /5 had a 4 speed transmission with a kickstart (as well as electric start, of course, common to all BMW bikes after 12/1969). Later in production BMW phased out the kickstart, but kickstart transmissions were available on some models on special order or on Euro models, and can be retrofitted. 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 very weak, and the kickstart on them is not to be used except in emergency.
Many early SWB bikes were converted to LWB, and there often is no big reason to do so. The pre-1981 5 speed transmission can be installed in earlier models. 1981 and later 5 speed installations to early bikes requires a change to the input shaft, pricey! Although there are some things one needs to know,... in general, early and later transmissions can often be interchanged, in both directions. 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 has VERY pricey parts these days, and few know how to properly overhaul them. I suggest Tom Cutter or OAK Okleshen or Ted Porter or Bob Clement. There is a comprehensive transmission article on this site that covers BOTH the 4 and 5 speeds: transmission.htm
The /5 models used a 180 watt
alternator, adequate for its purpose, but having little reserve for more than an upgrade to the H4
headlight and a bit more. Then it is BARELY adequate for a heated
vest, and perhaps 4 LOW power running lamps. In 1974 a
280 watt alternator was produced, and ONE specific version of that alternator for 1974 and PARTLY
into 1975 was such that the 280 watt parts will fit the 180
equipped /5 motorcycles, plug and play. After sometime in 1975, the
alternator stator parts do not fit into the /5 timing
housing. ***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
I will explain this alternator interchangeability more here:
The 180 and early 280 watt
interchangeable alternators both had a 105
mm stator outer diameter, the later ones that cannot be
retrofitted are all 107 mm. The alternators varied in
output over the years, with 180 on the /5, 238 on the R90S
and 250 or 280 on all the others. I've never figured
out, totally, all of the 250-280 situation. 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 lowered output. The
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 less resistance. Some BMW's had
rubber-mounted diode boards which were VERY troublesome, and
caused charging problems, breakage and aging problems,
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 the books on all the other models as 15, 16, 28, and 30 ampere-hours sized, in truth just two fit everything. Generally those are known as the 20 (or 17) and 28 (or 30).
The 500 cc engine was eliminated in 1973, but a 450 size, the
R45, VERY rarely seen (and never officially imported and
sold in the USA) in the U.S.A., was produced from 1978 into
1985. NOTE that 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....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 (R45N),
'beginners' could legally ride a big bike, with a lower output
engine. For a bit on the ratios, see my
The 600 cc R60 engine was 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 ones 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....not that such throttle use is good for ANY gasoline engine, actually.
The R50/5 is not adequate for two-up freeway riding. Neither is the R45N and R45. In fact, they are marginal for any freeways, without a passenger. The R65 is far better than many think, and will carry two-up on the freeways.
While most early bikes came with 18 inch front wheels (R45, R65) or 19 inch front wheels (most all others); all had 18" rear wheels. This changed with the R80GS and R100GS and the later R100R bikes...depending on model you could have 17, 19, or 21 inch wheels.
The Paralever came about in approximately 1987, but all the
bikes were not so fitted. All Paralever bikes are mono
rear, but not really the same as 'the' Monolever, although
there are similarities.
The Monolever can be swapped relatively easily into a twin shock model.
/6: The /6 began in 1974 with mostly cosmetic changes. The bullet headlight went away (BOO HOO), but a 5 speed transmission was now fitted. A new size engine was added, the 900cc, and a famous sporty model, the only one ever made that was equipped with Del'orto carburetors, the R90S, was introduced. 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 99mm. The pushrod tubes also changed to 18mm. It is unclear that the alternator bore in the case was 107 mm from 1976 in 100% of bikes....at least one 105 mm 1976 year has been reported to me.
/7: These actually began production at the end of 1976 and the 900cc model was abandoned in favor of the 1000 cc model. An 800 cc model was introduced for the 1978 model year. If the the 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 and 1978 R100S and R100RS had holes drilled at the factory for better breathing, probably helped with the hot air intake too.
The early R65 (and R45) models as I have noted above were SWB and in the mid-eighties, the larger frame was used, and the R65 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 late models. BMW also had 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, while earlier R65 models 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 (that 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. As I said, the relatively beefy front forks top triple clamp is such an instance of one of the things that was quite nice about the R65. The R65 used the different type of instrument pod common also 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.
The ignition system was changed in 1979 on all bikes to a canister that had a better drive method off the camshaft, and in 1981 that points canister was changed to a Hall device type canister. In that same year, 1979, and later, BMW changed to a single roller timing chain which is just as good as the prior duplex chain. The points canister, as well as the earlier types, is reliable, but, like all points, does 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 (ATE front brakes, the swinging caliper type). 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 the owner's booklet may say differently! The /5 through 1980 models can have coil failures from this abuse, and the 1981 and later models can have the electronics AND coil(s) fail. BMW used TWO single output 6 volt coils in series on some bikes from the /5 onward, and 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 around moisture.
There can be a LOT of 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; AND, much later for Authorities use. A FRAME may be identified with a xxx/7 tag at the steering head, yet not really be a /7. This has been a point of controversy and argument, for silly reasons. Basically, BMW stopped adding slash numbers, and this confused things even more.
The fully faired RS and RT models were QUITE an innovation when they were introduced, as they became THE long distance touring bikes of choice. BMW did wind-tunnel experiments when these fairings were designed. These faired bikes made a big impact upon the motorcycling world. The RS was introduced in 1976, but few are around. The RT came in 1979.
The highest power bikes were the R100 series of the late 1970's (up into 1984 for FOREIGN shipped bikes). BMW began in the very late 70's to make changes, of all sorts of types, including camshaft, exhaust, valve size, carburetor size, and compression ratio, to comply with U.S. smog requirements. Earlier bikes need premium fuel, later bikes use regular grade. There is a lot to know about the valves problems, an EXTENSIVE article is on this site. valves.htm
The Brembo rear disc brake caliper was introduced on the
R100RS in 1978, and the R100S and R100RT in 1979. The
Brembo front caliper(s) and the Magura on-bar master cylinder
came about in 1981 for ALL. 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 made by single spot calipers that were fixed, and
looked something like the Brembo's.
After 1981 linings were NON-asbestos, which means little. Squealing of brakes is fairly common, and the brakes.htm article discusses this. As I mentioned, earlier disc brakes used ATE calipers, and there were two types, one type had a 'swinging' adjustment, and the lesser known type looked a lot like the early Brembo caliper.
BMW stopped production of the R100 airheads for the USA for a period of time, with a model series known as the Last Edition; and then, due to screaming by enthusiasts, restarted production for awhile. It was all a bit messy. During this off-production 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.
As noted well above, 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).
The R100 cylinders won't fit the R90 cylinder heads.
If you contemplate making piston/cylinder/head types of changes, DO SEE my technical articles index, including #60.
Between 1979 and 1980 the swing arm housing size got larger, and the driveshaft design was changed, and the driveshaft with the torsional stress relieving spring and cams was introduced.
Fitting of oversize tires on the early bikes can be a problem with fitment. The front fork brace on some models might need to be replaced. For the rear, particularly if prior to 1981, you may need one spacer changed, not expensive, and very easy to change. Still, SOME 120 size tires of SOME manufacturer's will NOT properly fit, particularly on the disc brake rear models. 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, but SOME 120 x 18 are much too wide. In general, the 110 size is FINE.
The forks were changed fairly radically INternally in 1981, to a WORSE fork. At the same time the rear drive housing casting was changed, sidestand modified, the master cylinder was now a Maguro type located on the right handlebar. That was a good change, eliminated the often leaky, hard to bleed, and cable driven master cylinder under the fuel tank. In place of where the under-tank master cylinder WAS located, was now installed the heatsink/mounting for the electronic ignition module (needs to be removed and heat sink paste renewed every couple of years). Brembo disc brakes were now fitted in place of the ATE. The ATE 'swinging caliper' brakes can be OK, but one needs to know how to adjust the eccentrics. There may still be an article on the Club website, www.airheads.org, about that. 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. Also, as noted above, ATE DID make a type of brake caliper that is similar to the Brembo, it is NOT the ATE 'swinging adjustment' type, and in fact LOOKS like the Brembo, except for the ATE cast into the outer area, and the color. The 1979 R65 was one of these. These are EXCELLENT brakes, and a bike converted to twin front discs with this ATE non-swinging caliper and proper master cylinder piston size CAN stop VERY well; you will think you have 4-spot brakes. When converting, one may want to keep the original single brake disc master cylinder size...that usually works out quite well. I have converted some by going to bars type round MC, which works very nicely.
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 are a bit more work to adjust properly, whilst the Brembo 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.
In the U.S. models from 1980, the compression ratio was lowered, to allow lower octane fuels and as part of the upcoming 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. Several folks on the Airlist will do this type of work properly. BE SURE to get someone with MUCH experience and knowledge. This milling is usually done at the time the heads are converted to dual-plugs, which are of some advantage for fuel mileage, ease of starting, octane requirements, etc. Going to different intake spigots and carburetors can further improve power.
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. The 1981 frame was not the same as the 1982 and later twinshock models....and the 1981 was particularly hard to put on the centerstand....a kit is available. The 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 was still having neutral and overshifting problems, and that did not get fixed until 1982. Basically, whenever BMW introduced radical changes, there were bugs in them, witness the 1974 and the 1981 bikes. Oak has said 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.
In 1981, the newly introduced front forks were simplified, noisy (fixes came later), and I think they did not work as well as earlier forks.
Late 1977 to early 1980: cast iron valve seats had troublesome heat treatment, highly variable. From late 1980, to 1984, the type of seat material was changed, and gives a different sort of problem, although related. Prior to 1981 models, using unleaded fuels was bad for the valves. 1981-1984 bikes had a serious problem with the valve seats in the cylinder heads, there is an article on the valves/valve seats on this website, detailing it in great depth. That is a must read! BMW had some SERIOUS problems with use of UNleaded gasoline's, for ALL models until 1985 when they made a final fix. This has been discussed in depth, many times, in AIRMAIL, and I have done an extensive article that is posted at http://www.airheads.org . This is very worthwhile reading. The noted extensive article, valves.htm, (that is a hyperlink to the article) is located on this Snowbum website....and should definitely be read as it has been UPDATED, and is the preferred article. It is one of THE important things to understand, as an owner, or prospective purchaser.
In 1982 some gears in the transmission were changed, from a 15° angle to 17.5°. The parts do not work if MIXED, 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. As noted, if you have a 1974 transmission with serious problems, you may be forced to upgrade....see prior information on this page. The transmission article is MUCH more extensive in describing all these things.
There are rumors that the crankshaft was 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.
Sometime near the end of 1980 BMW lightened and greatly modified the clutch parts. Since model years crossover with production time, it is usually called 1981. The earliest diaphragm springs were weak for very hard use and discs were poor and blew up. 1981 clutches should be updated, when they are overhauled.
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
If the flywheel is removed, the rear face of the engine is 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. These signify the production month of the CASTING.
Some engine blocks for replacement purposes were made without any serial number of the type normally seen on the pre-1984 models, that is, at the dipstick area. 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 are no serial numbers on those replacement engines.
1977: valve covers can not be reversed anymore and the RECHTS & LINKS for right and left on valve covers are located on the INSIDE of the valve covers; alloy pushrods with steel ends quiet the valves a wee bit 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. Instruments still had white numbers, but RED needles. The area below the steering head is strengthened; RS introduced and gets a larger diameter exhaust pipe system. The cast wheels, called Snowflake, are introduced. The FRONT wheel only, and ONLY 19" cast wheels of production BEFORE 10/82 have ALL been recalled...see 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 started 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 INside the engine; rectangular aircleaner; 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.
1981: light weight clutch and the flywheel eliminated in favor of lighter 'clutch carrier'; electronic ignition; larger sump; modified clutch lever; brazed-on pushrod tube collars; different input shaft on transmission to match the new clutch; Nikasil. Engines vibrate more...generally....and are more touchy to get smooth with carburetor adjustments...due to the lighter clutch components. 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.
1985: On demand no-servicing type of wheel bearings; much quieter valve gear now having different components and the end clearance of the rocker arms is set by shims.
Late 1984 (???),
but for sure from sometime in 1985 TO 1993, and maybe even as late as some of
1994-5: BMW abandoned the use of a part
(circlip) in the transmission, and made a few other associated
changes. MANY transmissions have failed due to this. See Transmission.htm .
Noisy or vibrating operation, or feelable (sharp bits) metallic particles at the transmission magnetic center drain plug are cause for investigation. Other tests are appropriate, some should be repeated often. NOTE that some of the same sort of vibrating symptoms can be the Paralever bearings and U-joints. The transmissions can be updated (de-dated?) relatively easily, if costly. NOTE: If one has sudden unusual vibration in the transmission, stop riding NOW!!!!
Last of the Airheads: Some models were produced into the 1990's. R80GS, R80, R80RT, R100RS,
R100RT (to 1994+), R100RT Classic. A new model, the R100R model,
was produced in three versions, R100R, R100R Mystic, and R100R Classic,
and produced between 1992 and 1996. There was also a R100RT Classic
produced in 1995-1996 that was never imported.
Some of these various bikes, besides as noted
above, were NOT imported
by BMW into the USA. These R100R bikes all had the latest fixes, of which
there were not many...BUT: The transmissions, at least prior to 1995 (see
transmission article) might not have the circlip, an expensive problem if the
transmission fails. I recommend you read this article: transmission!
The R100R versions 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 R 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 the R100GS. The exhaust system
was different from earlier Airheads, and the instruments-group styling is a
matter of one's personal taste (there were at least two versions of them too).
The saddlebags were like the Tour Bags on the K bike models. One's
shipped to the USA had the 32 mm carbureted motors, and a change to the
Euro spigots and 40 mm carbs; and changing to higher compression pistons
will really improve acceleration.....this could 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 handling and least problems.
MISCL notes: BMW made some models seldom seen, particularly in the USA. The R45 and R45N
are VERY rare in the USA. There were Police (Authorities) models of many Airheads.
One 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 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.
04/17/2003: minor typos and clarifications, some major
05/10/2003: Add information on VIN numbers at top of page, and set space for additional serial
and VIN number references. Minor clarifications, 247-248, etc.
07/20/2002: Brembo & Magura information; transmission hyperlink & transmission dating note &
clarity of wording.
12/06/2004: Re-arrange the placement of some information, add more hyperlinks; add some things
deemed important that had been left out previously. Clarify a few details.
10/06/2006: Update 1974 information
11/05/2006: Some editing
04/14/2007: minor editing
06/10/2007: Article number removed, editing entire article for clarity, page placed before all the
rest on the T.I. page.
11/27/2007: previously had no article ID number, now is 67B
02/03/2008: remove hyperlinks to engineinternals.htm
07/20/2008: typos and clarifications only
10/24/2008: update article
11/10/2008: minor clarifications
02/23/2009: a couple of minor clarifications on rotors and stators
02/24/2010: Quite a few updates, to help primarily with identification
06/05/2010: notation regarding 105 mm alternator being seen on 1976 engine case.
04/09/2011: Minor updating, and a bit more on 04/19/2011
08/29/2011: Add link to Verrill's site page
07/24/2012: Just minor cleanup
03/01/2013: Clarified a few details.
07/27/2013: Clarified details on transmission gusseting for 1978 and 1979.
08/06/2013: Had a request to expand the R section, so did so.
© Copyright, 2013, R. Fleischer
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