Model differences over the years
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models.htm-67B

Before getting into the differences, let me clear up something about identifying year of production by VIN number.  Beginning in 1980, U.S. shipped bikes changed from a pure serial number to a Vehicle Identification Number.   This new type of 'number' is always 17 characters in length.  The TENTH position/character from the left beginning is the YEAR of production.  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 may not use the 17 character VIN number system.  In every case, the last SEVEN NUMBERS will fully identify the year and model....IF...IF!....you have the BMW factory or other charts information.   You can get that information from the Internet.  For VERY considerably  more information on VIN and Serial numbers, sequencing, etc. see the following article:
IDnumbrs.htm

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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 from 12/1969.   This article, in brief, DOES have a small amount of information on models prior to the /5...to set some background.

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.  A detailed discussion of the various models prior to the /5, is NOT included here. Suffice it to say that BMW had some radically different bikes from 1923 to the end of WWII.  Overhead cams, single cams, dual cams, supercharged.   Bikes described as the /3 were produced BEFORE the /2.  Early models withOUT slashes were built.  Some single cylinder models like the R26, R27, R28 were built, that were essentially the same as the twins, except for the motor.    For a discussion of some of the confusion on the early bikes, refer to:
http://w6rec.com/duane/bmw/slash.htm

There are a few knowledgeable folks that specialize in working on ""/2"" era and earlier airheads.   One in particular is:
Bench Mark Works, Craig Vechorik ('Vetch'), 3400 Earles Fork Road, Sturgis, MS, 39769 USA, (662) 465-6444    http://www.benchmarkworks.com
/5, /2, G/S, ST owners....and some others....have their own website.  See the  URL.HTM article
NOTE, however, that the MAIN source of information is not the single model sites, but the Airheads LIST. See the Technical Index page for information on how to get on that LIST.

BMW has tended to find ways to use up old parts bins stocks, and has shipped various combinations of components.  Also be advised that it is fairly easy to swap many items.   There is a lot of interchangeability possible on parts and components, although this is NOT to be taken that all can be interchanged.  There can and are very specific problems in interchanging SOME items.   However, all that being said, it is ALSO possible to put some items from other BMW bike lines onto airheads.  The K bike front ends and brakes, for example.   Those thinking of swapping airhead cylinders, cylinder heads, etc., should consult the Airheads Beemer Club internet LIST, for expert advice, although there IS SOME information in my  #60, ETC articles, and information on other things, like driveshafts, rear drives, fuel tanks and seats, etc., are found scattered in the appropriate areas on this website.

NOTE: NOT all models were shipped to the U.S., in any given year.  In fact, BMW stopped shipping R100 engine bikes for a couple of years in the 1980's.

In late 1969 BMW began the /5 series.  The /5 was a radical departure from the 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, and a separate bolted-on rear sub-frame was used.   I do NOT consider the new sub-frame as an improvement.   The swing arm type of rear end, incorporated a bit earlier, was retained, and the much older plunger design abandoned forever.  The engine had a considerable amount of change.  Mechanically, the biggest change was to move the camshaft location, it moved to below the cylinders, this improved oiling, the pushrod tubes delivering the oil from the top ends to the camshaft lobes.  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 a points & coil type of ignition.   A starter motor was added.  These were MAJOR improvements, but DID eliminate the super-classic feeling and sound of the /2 to some extent.  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 oils can extend the time between crankshaft slinger cleanings.

The internals of the wheels of the ""/2"" era bikes are very similar in basic design to the /5 and even into /6 airheads. The /2 era bikes had beefy axles and frames, DESIGNED for sidecar use.    The /2 era bikes steering heads had ball bearings, which was NOT as good as the /5 and later tapered bearings; and the /2 era steering head bearings can be relatively easily changed to the later tapered roller bearing design.  Medium capacity alternator conversions are available, as well as many other items.  The /2 series ended the use of the very nice looking early type turn signal housings.  The /2 era also 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.

There were improvements made over the years that were not so radical.  Many small changes added up.  One such modest change was the incorporation of a longer wheelbase in mid-1973 and the later addition of a cushioned driveshaft.  The earliest /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).  The 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 quite high.   Thus, BMW elected to go to the LWB (Long Wheel Base).  This also allowed for a bigger battery.   Frankly, my personal preference is the SWB. It feels quicker-handling.  The /5 bikes had 10 mm flywheel bolts, and the 1974 /6 also did...these could be twisted off from rider abuse during riding.

The 1974 was a not-so-good year.  The new /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.   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).  Finding neutral was often difficult, and overshifts also happened.....and the problems were not really fixed (well, mostly fixed) until 1976.   Some 1974 transmission parts are now NLA, and brand new transmissions are often the best answer to trying to rebuild a 1974 transmission.   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.   The 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.  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.

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.

Other changes 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.    

In 1979 a different system of driving the ignition points came...the "canister".  That canister contained points for just the 1979 adn 1980 years, and worked well. In 1981 the same canister was used to house the trigger for the new electronic ignition. There is nothing seriously wrong with any of the points-types ignition.  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, and engine timing setting...all 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 LIGHTLY lubricated at the felt pad and points cam, then with a booster or amplifier, the points life will TRIPLE, yet be EASILY field-repairable if the booster-amplifier should fail.   The1981+ electronic ignition is quite reliable, very powerful too...for reliability you must NOT pull off the spark plug caps whilst running.  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 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.  

BMW made changes to the valve gear over a long 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.  BMW added 24 small black rubber inserts into the head fins, to eliminate fin ringing. 100% of ALL valve gear changes, in part, or in total, can be installed 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 clutch, see the above Craig Vechorik's website.     NOTE that the 1981 (only) clutch was weak, and some 'blew up'.   Anyone with a 1981 clutch being worked on, should update to the later parts.

Nikasil (or, by another company also making the cylinders:  Galnikal) is a special coating in the cylinders, which could now be made of all-aluminum, the 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., of the old cylinders is IMproved.   The new cylinders can NOT be bored to a larger diameter, but if damaged may possibly be reclaimed by one of several specialist companies.  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 bore and recoat oversize.  BMW does not offer oversizes, just fitted sizes for these cylinders. Other manufacturers may.  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!

 In 1983-84 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 front wheel, and 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 simply 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.   (btw, 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.   There is no wheel bearing as such, the function taken over by the bearing INside the rear drive.   The disadvantages are that when that bearing does wear, it is costly to replace it.  Another is that a twin-shock rear end is better suited for use with a sidecar.   Many a Monoshock or Paralever bike is pulling a sidecar, however.

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, this was a supposed improvement on the Monolever, that added 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 liked it, always having previously faulted or looked down upon, the reliable BMW shaft drive bikes.    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 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%, but all seem to help with longevity.   There are fixes that rebuild 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.

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 (750cc).  

ALL the airheads until production ceased in 1995 had two opposed cylinders.

 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 wired to not allow the starter to be 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 SEEMED to tell the owner that the battery was near dead, and the sound produced is called 'the cricket'.  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

 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 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 kind of pricey and NLA. 

 The /5 had a 4 speed transmission with a kickstart (as well as electric start, of course).  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.  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 is no big reason to do so.    The pre-1981 5 speed transmission is retrofittable, just a bolt-up, to the /5.   A later 5 speed requires a change to the input shaft, pricey!  The 4 speed transmission has VERY pricey parts these days, and few know how to properly overhaul them. I suggest Tom Cutter or OAK 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 no reserve for more than an upgrade to the H4 headlight, BARELY for a heated vest, and perhaps 4 extra small running lamps.  In 1974 a 280 watt alternator was produced, and the 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.   After sometime in 1975, the alternator stator parts do not fit the /5 timing housing   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 the 250-280 situation.  The 238 watt R90S had a very slightly smaller diameter rotor in the alternator, which was done as crankshaft whipping was believed possible on that model. It's really a moot point, as almost all the rotors are really the same now.  The alternators of over 180 watts use a different diode board, but the later board CAN be used on the /5 models but not VV, except in emergency.    Some BMW's had rubber mounted diode boards.  VERY troublesome, and should be changed to aftermarket solid mounts.   

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 rare in the U.S.A., was produced  from 1978 into 1985.  The 600 cc engine was eventually eliminated in favor of a 650 cc engine, the R65.   BMW has made single cylinder engines of 250 cc capacity, and twins of 450, 500, 600, 650, 750, 800, 900, and 1000.  For licensing reasons, the 1000 is really 998...that idea is throughout the line.

NOTE:  The R65 650 cc bikes perform favorably compared to the larger 800 cc R80 bikes.  The R45 450 and R65 650 size engines 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 able to be run for enormous mileages at very high speeds/rpm, continuously.   The R50/5 is not adequate for two-up freeway riding.  Neither is the R45.  In fact, they are both a bit marginal for any freeways, without passenger.

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.

/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 transmissions had problems, as has been noted above.

/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.  

There is a R65 (and, I think, R45) model produced from 1979.  The early R65 were SWB, and had very nice thick castings for the top triple clamp, a handling improvement. R65 had 18 inch front wheels.  Most all early airheads had as stock as 3.25 x 19 front wheel and 4.00 x 18 rear wheel.  The R80 G/S which was produced from the end of 1980 in two versions, depending somewhat on year, had a larger front wheel, of 21 inch.   BMW installed tubeless rims and tires on some later models.

The R65LS was produced from 1982 into late 1985.  It had some things often thought of by SOME enthusiasts as a 'cheapening of the bike'.  It is really not that bad.  They did have compound wheels, whilst earlier R65 models were very similar to the larger airheads of the same year, except for the short wheelbase type of subframe, and in some FEW instances some things on the R65 were MORE desirable.  The early R65 had a smaller clutch, the later ones (1980+) had the same clutch as the larger engine models.  The 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 G/S-ST/R65 type.  There were some weird very technical things with those R65 instruments, but nothing of great note.   Later R65 had the larger frames, as BMW standardized.

It should be noted that the ignition system was changed in 1979 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.   The points canister, as well as the earlier types, is very 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.   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.  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 has 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 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 plain old 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 introduced, and they 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.  After 1981 linings were NON-asbestos, which means little.   Squealing of brakes is fairly common, and the brakes.htm article discusses this.

BMW stopped production of the R100 engined airheads for a period of time, had 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.  

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. 

The 1976 and later cylinders have a different sized BASE, they previously were 97 mm, and now are 99 mm, and won't fit earlier models.    Also, 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 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, cheap, and very easy.  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.

The forks were changed fairly radically INternally in 1981, a much 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.  This was a good change, eliminated the often leaky 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.  It should be noted that every model with a single front disc can be converted to a dual-disc.  BMW offered 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, it should be noted that 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 CAN stop VERY well.   

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 are of the twin leading shoe type.  

In the U.S. models from 1980, the compression ratio was lowered, to allow lower octane fuels.  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.     

1981 models, additional notes:   1981 brought about MAJOR changes, some of which are already noted herein.  Electronic Ignition, Nikasill/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, unleaded fuels were not very compatible.  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.  This 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.  A companion and very extensive article, valves.htm, (that is a hyperlink to the article) is located on this Snowbum website....and should definitely be read.  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.

There is some 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.   

In 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.  1981 clutches should be updated, when they are overhauled. 

Additional notes:

1977:  valve covers can not be reversed anymore; 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.   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).

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.

1981:  light weight clutch and the flywheel eliminated in favor of '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.

1985:  replace 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 (maybe a bit later, such as mid 1985, unsure so far) 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.  Transmissions have failed due to this.  See Transmission.htm .
Noisy or vibrating operation, or feelable metallic particles at the transmission drain plug are cause for investigation.   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!!!!

Revisions:
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 and Magura information; transmission hyperlink and transmission dating note and clarity of wording.
12/06/2004:  Re-arrange the placement of some information, add more hyperlinks, and 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

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