Snowbum's BMW Motorcycle Repair & Information Website

The /5 bikes had the BMW-classic black bullet headlight and instrument shell and used a 'stick' one-key-fits-all type of ignition/lights key.  Thus, the only real locking security is a standard type of key lock located in the steering head area, although most bikes (including later ones) were shipped with a cable lock, kept in the upper frame backbone that runs beneath the fuel tank.  The key to that cable lock was different from any other key BMW used.

The speedometer/tachometer unit inside the /5 headlight shell is a fun and games job to remove 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.   There is something very special about riding behind that headlight shell (and mostly similar to the /2 series too).

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 /5 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 that relay was 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, https://bmwmotorcycletech.info/slash5cricket.htm. Later Airheads had a more conventional relay, without the transistor, and there was no similar 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 number ending in /1, /2, and the more commonly used slightly later one on the R75/5, the /3 and /4, had many problems.  There is an article devoted to those early carburetors on this website:  https://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 riding in specific circumstances, which you'll probably not figure out how to duplicate (unless you have too-loose steering head bearing preload; and/or also have a steering mounted fairing and maybe some rear area large items or weight), .....instability was noted.   Thus, 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 but hardly exhibited the instability). 

The /5 came with a conventional incandescent lamp which was 40/45 watts; and while the lens and reflector worked well with that lamp, the light output was generally thought to be insufficient.   Halogen H4 headlamps came with the /6, 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 and reflector assembly, see https://bmwmotorcycletech.info/lamps.htm.   While on this subject, please take note that the outer lens used on all motorcycles is NOT the same for right-hand-drive countries, as for left-hand-drive countries.   The proper combination of metal shields of the lamp itself, and the lens and reflector, are what is necessary.

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.  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 (forward), and a simple fix is available, see  https://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 the motorcycle has a fork-mounted windshield; and, perhaps, if heavy rear loading (esp. on a rear rack) is used.

The pre-1981  5 speed transmission can be installed directly in earlier models. The pre-1981 transmissions had a longer input shaft than later transmissions.   Installing a 1981 and later transmission into early bikes requires a change of input shaft, which is pricey; or, machining work; or, the new style flywheel (clutch carrier) and clutch.  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 various 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:   https://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.  In any event, all 105 mm alternators fit the /5.

Expanding the information:
The 180 and early 280 watt interchangeable (physically) alternators both had a 105 mm stator MOUNTING AREA outer diameters, the later ones that cannot be retrofitted to the stock timing /5 or early 105 mm /6 timing chest 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 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, such as on the /5 or into the /6 with mechanical voltage regulators, were ~7 ohms, and succeeding generations of rotors had 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 physical size 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 physical sizes and ampere-hour sizes cover what is needed by all the Airheads.  Generally those are known as the 20 ampere-hour (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 https://bmwmotorcycletech.info/ringgears.htm.

The 600 cc R60/5 and R60/6 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 (1986) used the larger engine-sized frames.   An R65LS model was produced with compound construction wheels and it had many differences compared to the R65 mono model.   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 shank size of the valves are not as large, so they might overheat if lugged too much.

The R50/5 is not adequate for two-up freeway riding.  Neither is the R45N and R45.  In fact, they are marginal for freeways even without a passenger.  The R65 is far better than many think, and will carry two-up on the freeways quite decently, especially if a 'slippery' frame-mounted fairing is installed.

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.

Some Airheads came with 18 inch front wheels such as the R45, R65, ....and many models from 1985. Most older Airheads had 19 inch front wheels, although the G/S models had 21 inch. Certain early "cast snowflake" wheels were recalled in ONLY the 19" size, and the recall still exists, and the factory will provide labor and a new wheel, although the silver wheels are NLA.  That leaves the gold wheels.   Details: https://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 on the GS models in approximately 1986/1987, 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.

/6:
The /6 began in 1974.  BMW introduced a wider spline on the rear drive, so the spline held up longer. The bullet headlight unfortunately went away.  A new size engine was added, the 900cc, the R90/6.  Also added was the famous sporty (S) version, the R90S. It was the only Airhead ever produced equipped with Dell'Orto carburetors.   The 1974 had the first 5-speed transmission, and into some of 1975, 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 stator mounting 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 most things interchangeably if one knows how. ...( for the wheel one changes the lowers and wheel innards).

/7:
Production began near the end of 1976 and the 900cc model was abandoned in favor of a new 1000 cc model.  In September of 1976, BMW introduced a radical, for the era, faired motorcycle, the R100RS.  It had an integrated instruments in the fairing, and its various engine items, such as carburetors, exhaust size, compression ratio, etc., produced enough power to cruise at very high speeds, with weather protection and increased comfort.  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 of the larger displacement models 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 for 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).  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 type of instrument pod which was common to the G/S and ST.

The later bikes basically had two styles of instrument pods, variations on 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, which Airheads, owners of those R bikes...or not...seem to have like/dislike opinions on.

The early 19" front snowflake cast wheels were recalled.   The recall is possibly still in effect, although only the gold-colored wheels are possibly still available.
https://bmwmotorcycletech.info/19inchrecall.htm

The ignition system was changed in 1979 on all BMW Airhead motorcycles.  The ignition trigger was still points, but was now contained, with a similar to prior models ATU, in a metal canister with a considerably better mechanical drive method off the camshaft.   In 1981 the ignition points were eliminated in favor of a Hall transistor device used with full electronic ignition; the control module being placed under the fuel tank, on the pedestal previously used to hold the front brake(s) master cylinder, which was moved to the handlebars.  The front brakes became Brembo, and no cable-to-master cylinder was used.  The brakes became considerably improved by these changes.    The points bikes (1970-1980) are reliable, but like all points do require regular maintenance.  As I noted, the 1981 and later ignitions have the solid-state (semi-conductor) Hall device & 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 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 Airhead models can have coil failures (and even condenser failures, etc.) from that abuse, and the 1981 and later models can have additional electronics failures from that abuse.  BMW used two single output 6 volt coils in series primary winding connection on many bikes from the /5 onward for many years.  BMW also introduced a single 12 volt coil with twin outputs on the R80ST and the G/S.  Eventually that became standard for 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.

For 1979, and continuing to the end of Airheads production, 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, associated chain guide and tensioning method changes.

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.   The faired bikes made a big impact upon the motorcycling world.   The RS was introduced in 1976, but there are few of the earliest ones.   The RT came to the USA in 1979 and caused a sensation in the bike press.   A few aftermarket fairings were also available for some years; and, 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 eventually incorporated a second exhaust crossover near the transmission, and this was used on both 40 mm carbureted 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, but with somewhat less acceleration, and a reduced top speed.

The highest power output motorcycles were the R100 series of the late 1970's (and 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 and at the same time continue with similar characteristics for torque flatness, etc.   Earlier USA bikes usually needed 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:
https://bmwmotorcycletech.info/valves.htm

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. Disc brakes were introduced with the R75/6 and R90/6, & the R90S received 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 later Brembo brakes and late seventies ATE non-swinging brakes, of such as the R65, have no adjustments at the caliper area. It is possible to improve braking by various means, particularly the size of the master cylinder. 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. 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 later 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; or, possibly BMW put a single disc on the ST and GS models to help front end handling. ATE made 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 had 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. https://bmwmotorcycletech.info/brakes.htm has nearly everything regarding brakes, and also a lot about various modifications.

The rear disc brake with Maguro-built master cylinder was introduced on the R100RS in 1978, and it had a Brembo caliper. It was installed on the R100S and R100RT in 1979.  It is generally believed, with considerable reason, that the REAR disc brake was installed for marketing purposes, as it is not as good as the rear drum brake.  BMW went back to a drum brake at the REAR, in the mid-eighties, on all Airhead motorcycles.   The Brembo front caliper(s) and the Magura on-bar master cylinder came in 1981 for all Airheads; which was an improvement over the under-tank MC, with its problems and with the associated cable.  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 operated by a cable to the handlebars lever; or, were ATE single spot calipers that were fixed, and looked something like the Brembo's, and actually worked better than the ATE swinging brake, for practical purposes.     Every Airhead that came with single disc brakes can be converted to dual-discs.  There is a fair amount to know, so, again, refer to  https://bmwmotorcycletech.info/brakes.htm.

After 1981 linings were non-asbestos.

Squealing of disc brakes is fairly common, and my brakes article discusses that and how to fix it.

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 brakes article.

As previously noted, BMW stopped production and importing of the R100RT and most other R100 engine'd models to 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, for 1986-7-8.  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:
https://bmwmotorcycletech.info/technical-articles-list.htm, including parts of the articles in #60-x.

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 and this has been most often seen when using metric sizes of tires.  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 twin-rear-shock years with rear DISC brake, 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, here:   https://bmwmotorcycletech.info/section5.htm

The front forks innards were substantially changed in 1981, and not for the better, in my opinion. At the same time the rear drive housing casting was changed, & the side-stand modified.   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 considerably later, still needing the heat sink paste renewed now and then.  Ignition module and coils versions are a complicated subject, see my ignition article, https://bmwmotorcycletech.info/Ignition.htm.    The last versions of the electronic ignition module used a permanently riveted module/heatsink, that does not require heat sink paste renewal.

In the U.S. models from 1980, the compression ratio was lowered, to allow lower octane fuels and as part of the coming change to unleaded fuel.  It is possible to raise the compression ratio with different BMW pistons, or to mill the head, or even turn (on a lathe) the cylinder base. The result is more power, and if not overly done, the use of non-premium fuel works OK.   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 OFTEN 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, and 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, really an updating modification to the earlier version....all of 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, and he likely measured, with quite some difficulty I would think, many castings.