Pushrod; throw-out bearing; lever at rear of transmission; cables (and problems with even brand-new ones); clutch carrier/flywheel, bolts, crankshaft end play, adjustment of clutch levers; crankshaft end play spacers. Preventing broken transmission clutch lever ears.
Copyright, 2014, R. Fleischer
Article 60, subsection 9
INPUT SPLINES Throwout article, this is a
for additional information!!!<<<<<
Under NO circumstances should the flywheel (or clutch carrier 1981+ models) be removed without blocking the crankshaft!
See article http://bmwmotorcycletech.info/flywheelremovalwarning.htm
You MUST block the crankshaft!!!
DO NOT TAKE A CHANCE!
It is true that many have removed and replaced an Airhead flywheel or clutch carrier without blocking the crankshaft, havinf had no problems.
strongly given here, is to take the time to make &
use at least my simple crankshaft blocking tool. If you do not use some sort of crankshaft blocking tool, & your
happen to move forward enough (does not take much pressure nor
have to move far!) to have one or both of the thrust washers fall off their pins, you can cause VERY serious damage as you attach & bolt-up the
flywheel or clutch carrier. At a minimum, if the forward thrust washer drops, you may be UNABLE to get it back on its pins without a LOT of work.
Do NOT chance it!
Since it is a MUST, in MY OPINION, to mechanically block the crankshaft from moving forward at any time during the process of removing/replacing a flywheel ((or clutch carrier as it is called on 1981+ including some 1980 models)), you need to know how to best do that. This can be done in several ways. I recommend you do NOT use 'a towel' between the front cover and the alternator rotor, as is sometimes done. I recommend a simple & neat method...just make a tool out of a piece of Allen wrench material, and weld a disc (fender washer) on one end, making the length such that the Allen end fits into the alternator bolt, and the disc end presses against the inside of the outer timing chest cover. Usually 3/4 inch overall. The length should be such that there can be some light pressure applied by the cover to the tool, the cover being screwed back towards the engine lightly (but not touching the engine case, ...again, LIGHT pressure). The tool should be just long enough that the cover can't fit fully home all the way. Obviously you don't want to tighten very much and DO NOT NEED TO! A further treatment of how to make this tool (and a photo of it) is in the TOOLS article on THIS website, item #8. (that is a hyperlink). Note that making that tool requires a small bit of welding. If you do not have a welder, or do not wish to have the tool made that way, you can just use a piece of allen wrench, OR, simply remove the rotor bolt and use a common bolt temporarily at the rotor, adjusting its depth to fit the outer cover. That above tools article on also has photos of the clutch disassembly and assembly tools...you may need one or more, especially if you have an early model. There is another place on this website with a photo, etc., of that tool. I suggest you go look at that article, NOW: Flywheel removal warning
>>>>SEE and READ IT!!!<<<<
Be sure the OT mark is in the timing window when removing & replacing the flywheel (or clutch carrier). Do this "removing & replacing" ONLY when the pistons are fully extended outwards. When the flywheel shows the OT mark in the timing hole, both pistons will automatically be fully extended outward if the flywheel or clutch carrier was already installed properly. If that is not seen, then the flywheel is mounted to the wrong crankshaft bolt holes. Many a person has goofed, so, be forewarned! Re-said: the flywheel is not 'indexed' & can be installed to the wrong crankshaft holes. The flywheel is also to be centered in the proper selected holes, by moving it back and forth very slightly CW/CCW in its holes, before being fully tightened. It may move a TINY amount if maybe the bolts are a turn loose...so find the centering position, then tighten carefully, and then torque to specifications.
Clutch parts, including flywheel or carrier, should be identified by marking with paint or punch pricks before you disassemble. BMW did that on some models. Parts are installed at 120° with respect to the BMW marks, which may exist, and may not. This is contrary to what the repair industry usually does, which is to align the marks. Frankly, when I mark things myself, I use one punch prick opposite the other, for the first markings; and the next set, if needed, is two punch pricks, then three, etc. Arrows also work. These are standard methods. I don't use paint or other marking methods, unless I would not need to find them, in the 'future'.
Re-said: In case factory marks are not seen, YOU mark your clutch parts (not disc nor diaphragm spring) before disassembly from the 'flywheel' or 'clutch carrier'. If you see factory marks, those marks are to be oriented so they are, as best possible, 120° apart to all of each other;....NOT lined up!
clutches had changes during and after production.
The replacement diaphragm springs were changed, and 6 spacers
were no longer used.
Spacers are sometimes added if parts have been resurfaced...but that is a whole special story by itself.
There were several types of diaphragm springs used, and the heavy duty type is usually stamped with the part number. That part was 21-21-1-234-035. Some call that the 'sport plate'...but it is the diaphragm spring.
There was a spring common to the R90/6 and R90S, 21-21-1-231-842; it is obsolete, NLA.
The pressure ring was updated, that is part of the spacer deletion mentioned above, and the new pressure ring is more rugged, and a better heat sink. If you are updating, the updated parts are the -035 spring; the 21-21-1-236-332 clutch plate which has an extra set of rivets and a plate, on opposite side, locks those.
Another later part to use is the 21-21-1-231-666 pressure ring. The early pressure ring had standard blade screws which should not be used; instead use 6 point head Allen screws, and torque to a target of 16.6 footpounds.
BMW made big changes to the
clutch/flywheel parts in the transition period between 1980-1981.
The flywheel as such was dropped, and a lighter 'clutch carrier'
was incorporated. The
throwout bearing was also changed in
design. These clutch parts are very
different from earlier models. The new clutch assembly
was lighter, and also
required much less lever force at the handlebars; but engine vibration
generally increased due to the lighter flywheel effect. The 1981
ONLY clutch parts (as
opposed to later clutch parts) were sometimes
very troublesome, and some nasty failures were seen now and
My comments here do not necessarily apply to the R65.
The initial clutch friction disc, called officially the clutch plate, was 21-21-1-242-370. A stronger
disc, under part number 21-21-1-451-512 was then used. The carrier, officially the clutch housing (or, clutch case), was 21-21-1-242-372; it was also beefed up, becoming 21-21-1-451-511, and then that became 21-21-1-338-722. Note that during early production of the 1981 bikes, some bikes
had factory installed washers between the carrier and the cover. They are NOT to be used when replacing these parts. The early carriers had 6 'ears'; later ones went full circle....so did not twist and distort nearly as much.
The 1981-1984 diaphragm spring was
and a higher pressure one IS available,
21-21-1-338-508 (which I recommend). There were other
updates. The pressure plate 21-21-1-242-354 became
21-21-1-243-009, which became
The rearmost part, called a
case lid or housing cover, was 21-21-242-355; and became
21-21-1-457-280. Bolts 21-21-1-242-371 became
you are overhauling a 1981 model with original parts, it is a VERY
good idea to replace all the parts that were updated ...which is nearly everything!
Clutch friction discs were asbestos in the old days, which had, I THINK, a better Coefficient of Friction, than today's replacement discs.
Brand-New discs are ~6 mm thick. When worn below the official limit, 4.5 mm, may slip. Slipping tends to show up first when using large amounts of power in top gear. I think that if the rest of the clutch parts are in reasonable condition slippage won't occur until maybe 3.5 mm. No hard & fast rule here, due to wear (cupping) on the pressure plate, wear on the diaphragm, etc.
I check clutch parts on a machinist's flat, but you can use a flat piece of glass, etc. You can use feeler gauges to determine the dishing, etc. Check disc thickness via vernier caliper or micrometer. Another way, very commonly done, is to determine if the parts besides the friction disc may need resurfacing or replacement, is to measure the width of the worn disc of the friction material (both sides together), near the outside edge, and re-measure near the center. If the thickness is considerably different, there is no official specification, but I'd say over half a mm, then all the friction parts of the clutch need attention. While there is no directly official specification, you could determine it from how BMW shows the various distances, etc....and find that to be ~0.3mm...disregard that, and use my half mm. Check the diaphragm spring with vernier for height, etc. See the specifications in the various literature. The diaphragm spring has specifications, and they vary with model, as to height and as-fitted pressure and when pressed flat. There is also a specification for the height differences of the spring fingers. Ask about these on the Airheads LIST. I suggest that only the unpressured height usually needs be checked (besides inspecting for unusual wear).
If you replace just a friction disc, and the mating parts are worn enough (especially if they are not be dead flat or flat enough) the clutch may slip...although if used gently, the clutch may break-in after a few hundred miles and be OK. Professional mechanics usually do a clutch job by replacing the three parts, but you CAN just replace the disc, but I would recommend checking the taper/flatness of the parts. The heavy duty higher pressure spring is a good idea, especially with these later non-asbestos discs on the early clutches.
Clutch PARTS can be overhauled. Southland Clutch can modify the old parts and supply a thicker disc, needed with their machining of the originals, etc.
See my REFERENCES article under C for clutch.
Disassembling the clutch:
It is important to unfasten the bolts evenly, in a criss-cross fashion on the clutches prior to 1981. On these early clutches, those bolts are NOT long enough to do this without a spring-loaded problem from the clutch. So, how to do it? You remove three of the six. In place of those three, you then install some long bolts and spacers ...from the hardware store....unless you have the BMW factory-type clutch tools. With either the hardware store bolt method or the factory tools, you can then undo the other bolts, evenly, in a criss-cross pattern, bit by bit, 3 of them will do. I reuse the early models bolts (I inspect them of course).
On the 1981+ clutches, you will be using new bolts. Use NEW special vibration-proof washers too!
On the 1981+ clutches, there is NO need for the above release method, simply remove the bolts. Note that these clutches can stick from corrosion at the bolting areas. Use a small flat blade tool, even a screwdriver, and gently pry a bit here, a bit there, and over a few minutes the clutch will come apart.
Here is a photo of the factory-type tools for the early clutch (including the centering tool): ClutchFlywheelTools.jpg
A SI was issued with a lot more information on where to grease the mating clutch parts....ETC. That is in the 1992 service fiche, page 4, G13/H13/I13. Basically, it is the contact points of the diaphragm spring. I use a moly grease there, very sparingly.
HINTS!!!.....exceptionally stiff clutch action can be due to a BAD CABLE; or, worn, grungy and even broken parts in the clutch throwout bearing area, including the bearing, piston, etc. Do NOT fail to change the clutch cable if bad;...it can FEEL OK with the cable disconnected at the transmission end, yet be very stiff when in actual operation. Do NOT have the clutch cable running with sharp bends; nor have more than the ONE tie on the right down-tube. Be SURE to grease the bar lever clutch cable barrel-end and barrel itself area (moly!), and be SURE that the cable inner strands are NOT fouled by the slot in the bar lever as you pull the lever back towards the bars or move the lever up and down. Yes, that means to ALSO wiggle the lever UP AND DOWN, to see if there is so much play in the lever bushing (nylon and replaceable) that some strands foul in the lever slot. It is especially important that the cable end, called a cable barrel, be free to rotate in the clutch lever. Crimped area at the barrel end must not foul the lever either, and you might have to file that a bit. Pulling the clutch lever slowly backwards will show by #1 eyeball if the barrel is moving freely. If not, unfasten the cable from the lever, and clean up any rough spots on the barrel, then re-reinstall, again using a moly grease on the barrel. If the nylon bushing needs replacement, do so. If it does not fit properly, then ream it SLIGHTLY. There is a waverly washer used in a machined depression in the clutch lever, the waverly washer must be there.
More information on cables and levers, etc: CABLES
If the clutch cable is not properly adjusted, the clutch can slip; the shifting can be bad, the hand pressure can be high....and more. The clutch can slip from a thin friction disc, worn parts, and also from throw-out bearing problems....I discuss that just below.
Throwout bearing, etc:
STIFF or no clutch or slipping...when engine fully heated up (or even when cold)?
This problem originally was reported now and then with motorcycles as late as the early 1990's manufacture! It is NOW clear that the problem exists, even if rarely, on the last of the Airheads, such as the R100R, and even with the "new" throwout bearing that BMW went to. THUS, this section was revised 05/16/2013.
On 1980/1981 and later
models, the PLASTIC (which looks like aluminum) or ALUMINUM 'piston' (yes, both types were made) with the metal center,
that the clutch lever at the back of the transmission applies its force to,
might be too large in diameter, and stick in the transmission bore
This piston is next to the 1
inch mark of the ruler in the photo
well-below. The LIMIT is 28.7 mm, and it
be sanded down, or replaced. This occurred because
of accumulated error tolerances on some transmissions throw-out area bore sizes, and
throw-out pistons. If the piston fits
into the bore a bit too tightly
....(it may still operate fine when cold), under some circumstances, PARTICULARLY
when HOT, the piston may stick. That is because the plastic piston material expands very considerably faster than the
aluminum bore it fits into. Obviously this means that a
proper check is with a hot transmission! FEW do THAT.
The problem can manifest itself in several ways, INcluding a hung-up or very stiff operating clutch, or a slipping clutch. Measure the piston, and if it is over about 1.13" (28.7 mm) when hot, you MAY want to reduce the outside diameter a bit. I have seen these as large as about 1.142" that still worked OK (NOT all at that diameter WILL be OK!!). It really depends on the transmission bore hole, but you won't be changing that.
I can't give a hard
and fast rule here, but if your throw-out piston is up to 1.141 or so, I would
certainly see how it fits, and if a bit too much friction with a
HOT PISTON, I would recommend sanding the OD a bit; keeping it concentric!! You might want to
check the fit, hot, if you have any hot clutch slipping problems or any stiffening or hung clutch problems, but OK when
cold. There have been some reports that the plastic piston expansion can happen and then be more or less permanent; after years of seemingly being OK. While the described modification can be done on a lathe with some sanding paper, you can also
chuck the rather short shaft tip end in a drill press and use
some rather fine sandpaper for this. The drill press chuck won't grab strongly on that short tip, so don't over pressure with sandpaper...take your time. The sandpaper and throwout unit should be DRY, NOT lubricated, during the sanding. Use a micrometer or vernier caliper to measure the piston diameter as you sand it down. Use a moderate speed of rotation. I usually just do this, rather than replace the assembly with the newer type. A shop probably would not sand the old part, but replace it with the updated part.
Inspect the bearing & if it looks bad, replace it. Grease it with a good thin grease (Do NOT use moly). While the bearing is theoretically lubricated by oil from the transmission, that is not hardly so for some miles after initial assembly....so use a quite soft & mild grease, non-moly.
>>>BMW has had several versions of the throw-out parts, and offers a replacement piston: 23-13-1-464-167, which is another, if somewhat costly, way of coping with a sticky hot piston....and if your old bearing is quite bad, and piston sticking when hot.....you could consider this part, as it is a new design, and incorporates the bearing, and it supposedly has the proper diameter. If your old items are in good condition, you really do NOT have to spend the bucks....you can sand your piston outside diameter. It has been said that there is a special surface coating on the piston, and sanding or otherwise machining is a bad idea. This IS NOT TRUE...sanding works fine, and lasts. Just do NOT remove too much material, or the piston could cant sideways. NOTE that at least one new-style piston has been reported as expanding and sticking!!!! I had TWO reports that a new-style piston expanded slightly and permanently, and gave clutch problems with the transmission being COLD. I personally have not seen this (yet)....and probably will not, since I have stopped doing work for others.
has also been reported to me that BMW MAY have recently shipped all-plastic parts that have
the same old problems!
It was reported in May 2013 that a R100R with original "new type" piston assembly was seizing, and was repaired by sanding or turning the piston down on a lathe, slightly. That was the first instance I had heard of this on a R100R. The R100R was the last version of the Airheads, produced into 1996.
|At this point, I think it appropriate to caution that if your clutch operation becomes faulty in some way after the engine is fully heated-up, that the throwout bearing be checked to see if it fits OK, when the engine/transmission is hot from a reasonably long ride. It is also a possible problem with the engine being cold, if the piston has permanently expanded.|
Be sure that no matter what part you have in YOUR bike, that it has not expanded and seizing up...measure the part...or feel the fit, transmission cold and when it is quite hot from the bike being ridden a decent distance, perhaps at a minimum, 20 miles.
NOTE: The 4 speed transmission had a balls type throw-out bearing; the 5 speed transmission (1974+) had a radial needle bearing type, and in 9/1980 BMW went back to a ball bearing, of a new design. Can you figure out why a radial needle bearing is a lousy choice, as far as pure engineering is concerned?....think, then read the next paragraph. (((thinking time...thinking time....)))
The radial needle bearing for a throwout bearing in an Airhead is a POOR design, but works fine! When RADIAL needle bearings are pressured (say, by a flat plate) and rotated circularly, the needles try to rotate at the same speed at BOTH ENDS of each needle....that is, from end to end of an individual needle. This is NOT POSSIBLE, if you think about it, so they scrape around....forcing any grease out. BUT, the bearings are NOT being constantly rotated, only when the clutch is used, and the transmission oil lubricates the bearing. Thus, the bearing does hold up OK most of the time see downwards a couple of paragraphs, for exceptions. If the grease (or transmission oil) is not there, and a little moisture condenses there, or excessive clutch hold-in times are often used ....and/or combinations of these things.....the bearing can start to deplete its lubrication, and actually freeze up. When you install the bearing, you lube it with a fine thin grease (NEVER a moly grease), and that grease will lubricate the bearing until the transmission oil gets to it enough.
NOTE: The 4 speed transmission and the early 5 speed transmission clutch push rods had felts located in a pushrod groove, and are installed best from the front. More to that, however, below.
NOTE: As noted above, the 4 speed transmission had a balls-type throwout bearing. The early 5 speed transmission had a radial needle bearing. From 1981, BMW BMW went back to the ball bearing. The radial bearing is, IMO, a poor design, and if it fails, the needles can flat-spot, the bearing can seize, etc. HOWEVER, that is RARE, and the ball bearing version also can fail, but hardly often. MOST throwout bearing failures are due to moisture getting into the gearbox!
Below is a picture of a 1982 felt-less clutch rod, the superior type ball bearing, piston with plastic outer, the internal spring, a new rubber accordion cup, and the band-clamp. The rod is about 9 inches long; the piston cup is about 17/32" wide on the DARK plastic portion.
As noted earlier....the
bearing is lubricated with transmission oil during operation; but
that takes time and miles after the throwout bearing
is installed;...so.... I always use a very
NON-moly grease when installing this bearing. NOTE ALSO that the "felt-less' clutch rods came in 1981.
Prior models of clutch
rod had a felt,
23-21-1-230-440, which is best installed on the rod, and the rod
from the FRONT of the transmission. It is possible
rear, with a homemade tool, but I recommend against
The felt IS necessary on models prior to 1981, otherwise the clutch disc can become oiled and thereby slip, and be ruined eventually.
1981 and later models have a lipped seal at the rear cover, not easily replaced....the transmission must come apart.
WARNING about the clutch arm!
Earliest models, the /5 that
is, had the clutch actuating arm at the rear of the transmission
held to the transmission, via a cotter key. Very
Later, but still rather early models,
had the clutch actuating lever at the rear of the transmission
held to the two bosses of the transmission cover by a PIN, that
used a single C clip. That C-clip fit on the pin at the INside
of the lower boss. If the C-clip came loose, the pin could come upwards, and come out of the lower boss, and the next clutch application could, and often did, break off a transmission boss ear...necessitating a transmission overhaul....or some inert gas welding at a minimum for a permanent fix (temporary fixes are of several types, not treated here). Often this happened while you were shifting, going down the road, and not in your garage...and the ear was lost...so it got a bit more complicated if you HAD-to make an ear or HAD-to, or wanted-to, replace the rear cover, which necessitates fresh shimming of the transmission, hence a overhaul is usually the best thing then. Restating: replacing a rear cover means re-shimming the transmission; so you might as well overhaul it. Fixing the problem before it happens, which costs VERY LITTLE, can save you a HUGE amount of money:
THE BEST FIX: remove the old pin and clip and install
#23-13-1-241-484 pin that has a flange, and won't fly
out. This is used with a clip that is part
It is also possible to use a bolt and a nut; I suggest a shoulder type bolt, and do NOT try to squeeze together the ears, they will break! The bolt just needs to be there, it does not need anything more....it can be finger loose (it is not clamping parts like you might think), you just do NOT want it to come out. Because of this, if using this method, use a self-locking nut, tightened JUST enough so the bolt has some slight free-play and is NOT squeezing the transmission cover ears!
BMW had a Service Information bulletin (we call them SI's), November 1991, #11-049-91, sub number 2495, and this can also be seen on the 12/92 fiche on page 3, G23. Basically, it stated that while the flywheel bolts were previously at ~75 foot-pounds (100 Nm), they were now to be at 90 foot-pounds (125 Nm), cleaned threads, and then the threads were to be OILED! BMW specifically said that the bolt limits would NOT reach their limit of elasticity at that torque, and could be REUSED! I will NOT tighten them that tight. Makes me very nervous! However, some do tighten them that tight, and I have heard of no problems reported. It is YOUR CHOICE. NOTE also that this is in regards to the 11 mm bolts, and applies to 1981+ models....certainly not the smaller /5 and early /6 10 mm bolts; which need replacement upon each use, which the 11 mm do not, and those 10 mm bolts in the /5 and early /6, are absolutely NOT to be torqued to such high values.
There have been a lot of different specifications on flywheel bolts over the years. There were two lengths of 10 mm bolts used. I use, clean and dry, torques of 42-45 foot-pounds on the 1973 and earlier engines; and for the 1974 I use 52-55 ftlbs; and 1975 and later up to the 1981 models, I use about 75 to 80 ftlbs. I use about 80 ftlbs, clean and dry threads, on 1981+.
Grabby clutch: If your clutch is grabby, it can be due to a number of causes. It is IMPORTANT that the transmission input shaft splines be regularly lubricated. When they get dry, the shifting is stiff and poor and may be somewhat difficult to get from 2nd gear down to first gear, or just to engage 1st. Never lube the disc spline, just the transmission INPUT spline. Cleaning and re-lubrication should be done at a mileage and time commensurate with your driving habits and atmospheric conditions and the condition you find the splines in during the servicing. Moisture condenses on the shaft and with the in-out movement during operation of the clutch, and the wiping action of the essentially gear-like teeth under torque, all conspire to move the grease out of the splines. Late splines were nickel-plated, and hold up a bit better and longer, regarding lubrication. Spline wear, if not lubricated, can lead to spline failure, a $$$ situation. I suggest a look-see and cleaning and lubrication of the transmission input splines at 15,000 miles since last cleaning and lubrication, and then adjust the mileage for the next following time. NOTE that end play of the input shaft can cause a quite-grabby clutch operation, and that can happen cold and/or hot. More often when hot. To fix THAT, one must remove and open the transmission and work on the shaft shimming. One can get an idea if that is a problem by removing the transmission, heating it to about the temperature of boiling water, and measuring, with a dial indicator, the input shaft end play. Anything over a few thousandths of an inch is suspect. This problem with transmissions causing a grabby clutch is not overly common, but it seems to be more so for the 1979 models. Grabby clutches can also come from a somewhat rare problem, the crankshaft has excessive end play. SEE THE FLYWHEEL REMOVAL ARTICLE WHICH HAS INFORMATION ON FIXING THAT PROBLEM.
It is possible for a bad throwout bearing to cause a grabby clutch.
Recommended greases for the input splines are here:
EZ-Clutch (and variations): The pre-1981 clutches have a heavier pull at the bars, some dislike that, or cannot easily physically cope with it. There are several types of modifications to fix this, besides the HUGE expense of installing a 1981+ clutch with its necessary transmission work. Modifications involve a single pulley device or a lever arrangement. One that is available for purchase is from Craig Vechorik ('Vetch'), dba Bench Mark Works. (662) 465-6444; located in the in the USA; www.benchmarkworks.com/articles/howto/clutch.html Bench Mark Works also has it available from their place in Canada. There is also a type you could build, that has some advantages over Craig's...as the original cable end can be used. Here is a website with photos to give you some ideas: http://www.frankhams.freeserve.co.uk/temporary_uploads/ezclutch_page.htm
is a round factory tool to centralize the friction disc when assembling the clutch to the
flywheel/carrier. However, your eyeball is good enough if careful.
If you want to make this tool:
The tool, overall, is roughly 133 mm long; and the length is NOT in the slightest critical. In fact, hardly anything is critical. I do suggest making the 20.7 mm diameter, as shown in the sketch, reasonably close to that.
My measurements are from the factory tool I have. clutch tool.pdf
Here is a photo of all the
factory-type tools for the clutch:
The tools are especially useful for the /5 clutch, but you do NOT NEED THE TOOLS. You can fashion something to hold any of the clutches from rotating while R/R bolts. You can use long cheap hardware store bolts and nuts to release the /5 clutch...etc.
Here is a hyperlink to my tools article: http://bmwmotorcycletech.info/tools.htm In that article will be found information on clutch removal and assembly tools.
Assembling the clutch:
Here is a major hint. Some of this is NOT factory information.
When you disassemble a clutch, for whatever reason, one of the things almost always done is to check the friction disc for thickness. This means from one side to the other. I do it near the outer edge, and at about 3/4 of the way towards the center of the lining. Other checks are the spring (relaxed mode) height, & condition of the other parts in the clutch assembly. New friction discs are about 6 mm thickness with some variation, fractions of a mm, over the years. BMW says to replace the disc at 4.50 mm. On an Airhead, getting to the clutch is pretty easy, so whether or not to replace a disc at 5 mm or even a bit less, is a judgment call. You might consider letting it go, so long as the clutch is not slipping in top gear with heavy throttle & goodly rpm, all of which are worst case for slippage to occur. One of the big decisions, & this is the HINT, is what parts need replacing, if any, if the friction disc is going to be replaced. You may hear advice that parts that push against the disc, on both sides, need replacing. But, how do you know? There are no specifications on the DISHING type of wear that IS one of the main reasons to replace those parts (& deep scoring, etc.). Some of us know what works, & what does not, & we might check 'dishing' with feeler gauges on a precision flat surface. Here comes your hint...
Measure the disc friction area near the outer edge, then in somewhat, & then near the inner edge. Do this with a micrometer, not the wide jaws of a vernier caliper. If the thickness is pretty good for all three checks, you are VERY LIKELY not going to need the other clutch parts. How much difference? Maybe 0.015" is about the max. but have seen more that was OK. If less than that as a variable, you probably can just replace the friction disc, only.
Unless the clutch parts are pretty flat, you can contact such as
Southland Clutch to machine your plate and make you a thicker
disc to compensate for that machining; or, you need to purchase
new parts. Many folks just replace the disc, and have to do
a clutch job all over again, soon enough, due to not checking the wear on the other parts.
Southland Clutch; 101 E. 18th St., National City, CA, 91950, (619) 477-2105, can resurface all models of Airhead worn clutch parts and supply the thicker clutch disc that is needed after those operations. Dan Levine. Dan@southlandclutch.com
Here is that previously mentioned hyperlink to my tools article: TOOLS.htm In that article will be found information on clutch removal and assembly tools
During your assembly (don't forget previous information on
marking the parts and 120° assembly), I suggest you coat the edge
of the diaphragm spring where it touches the flywheel and the
fingertips areas too, all with thick moly grease/paste....not very much!
This will help the spring fit properly and operate smoothly.
Remember: just a tiny coating.
Align the friction disc by eyeball or tool, and then torque, evenly, the clutch bolts. For the pre-1981 models you will need some sort of long bolts and some spacers from the hardware store (unless you have the BMW tools), and I have mentioned those long bolts earlier in this article, so you should have them by now.......in order to get the pre-1981 clutch to assemble to the point you can use its original bolts. You don't need more than 3 or 4 of these long bolts...three will do, as the clutch has 6 normal bolts, and three can be spread at an even 120°...you will also need some spacers for them. You install these long bolts evenly, criss-crossing while tightening them evenly, bit by bit, until the clutch is pulled together, only moderately. THEN you can install the original bolts, and torque them properly....one by one. For the 1981+ clutch, replace the clutch bolts AND the special vibration-proof washers.
clutches, and their bolts:
SOME 1980, and all 1981 and later bikes used Clutch Carriers, no longer are they called flywheels.
Did you have the flywheel off, the engine has rotated some, and you need to find out which crankshaft bolt holes and flywheel holes should be lined up?
Here is an edited question and reply I did to the Airheads List:
"" I removed the fly wheel at top dead center (OT mark in window) but when I installed the seal with the installation tool I ended up rotating the crank. How can I ensure that I am at top dead center so I can reinstall the fly wheel correctly?""
Since you have the flywheel off, I certainly hope you have a crankshaft stop of some sort, at the alternator bolt. If you don't, you are in danger of doing major damage as you install the flywheel....so, do it...and hopefully the crank has not already moved forward. If you think it moved forward, see my article and the sketch from Tom Cutter....both are on my website. It is Article 60, sub-section 2
direct link: flywheelremovalwarning.htm
I am not much in favor of removing that crank stop (so as to turn the engine with the rotor bolt), because if you should then allow the crankshaft to move forward, you could be in a world of trouble.
The safest way for you to go would probably be this procedure:
1. Remove the valve cover on the left cylinder and remove left and right cylinder spark plugs so the engine
is easy to rotate.
2. Place the flywheel into any bolt-hole positioning, lightly putting in a few bolts.
3. Rotate the flywheel slowly in the NORMAL direction, which is ANTI-CLOCKWISE as you face the
flywheel from the rear. Watch as the left EXHAUST valve CLOSES. Rotate more and watch the left
INTAKE valve. After the INTAKE valve closes continue to rotate in small amounts, shining a flashlight
into the spark plug hole. You will see the piston come fully out, then reverse. The pushrods, piston at
near or fully outwards, should be easy to rotate by your fingertips, and a double check is that both
valves are fully closed.
4. Rotate the flywheel CW and CCW a small amount until the piston is fully outwards, eyeballing it is good
enough! There is an explanation that could include the 72° per bolt hole which seems like a lot; but, a full
explanation would include it being less because the piston moves rather slower than those degrees
might tell you, as the piston comes out and near OT (the piston rod is extended), but we can disregard
that here. We can also disregard using a dial indicator, etc.
5. Some might use a round tip metal rod for 'feeling' the piston. Do NOT bugger-up the spark plug hole.
Do NOT use a pencil, it could break.
6. With the piston now fully outward, if the OT mark is not someplace IN the timing window, remove the
flywheel and reposition it so OT is in the window.
7. You can skip removing the valve cover in step 1, and then skip step 3, if you feel OK about 'feeling' for
the piston coming outwards. It does not matter which stroke you are on, just that the piston is fully
outwards relatively closely. I often do it with the round-tipped tommy-bar in the standard tool kit,
through the spark plug hole. Turn the engine, if you do it this way, very slowly and gently, so as to not
let the tommy bar hang-up and bend the spark plug threaded-hole metal.
HINT!.....The early R65 and R45 had smaller clutches than the larger engines did. The 1989 and 1980 had 6 x 1.00 mm CLUTCH bolts. The amount to torque the clutch bolts to the flywheel is NOT listed in early BMW literature; and is wrong in some later literature. There is some confusion over this. BMW originally had Allen head bolts, then later went to hex head bolts. I suggest using the hex head bolts. Some published figures are as high as 17 foot-pounds for the clutch bolts (any style). That is WAY too high, even for high strength bolts. I suggest 88 inch-pounds (7-1/2 foot-pounds), for the 1979-1980; and, use clean, dry threads, then coat before assembly with a light
amount of Loctite BLUE. It is possible that up to 10 foot-pounds is OK, but that would be for high grade bolts only. Any book figures you see that say 17 foot-pounds, or 15 foot-pounds, is WRONG!
Early /5/6....to 1974
had 10 mm flywheel bolts used on 93
tooth flywheels. There were two lengths installed. I will NOT
reuse them. Torque them
to book specifications,
dry. The flywheel was 11-22-1-256-966.
/6 in 1975 and 1976 had 11 mm flywheel bolts on a 93 tooth flywheel. The flywheel as 11-22-1-262-070. 11 mm bolts were used on all later models.
/7 for 1977 through early 1978, NON-emissions timing bikes had 11 mm flywheel bolts on 111 tooth flywheels. The flywheel was 11-22-1-263-788.
1978-1980 WITH emissions timing bikes had 11 mm flywheel bolts on 111 tooth flywheels. The flywheel was 11-22-1-336-380
The flywheel mounting uses the mentioned larger 11 mm bolts on all models after the 1975 change from 10 mm bolts. Threads were to be clean,
dry, NO Loctite used.
BMW Service Information bulletin (we call them SI's), November 1991, #11-049-91, sub number 2495, and this can also be seen on the 12/92 fiche on page 3, G23: Basically, it stated that while the flywheel bolts were previously at ~75 foot-pounds (100 Nm), they were now to be at 90 foot-pounds (125 Nm), this is with cleaned threads, BUT... the threads were to be OILED! BMW specifically said that the bolt limits would NOT reach their limit of elasticity at that torque, and could be REUSED! I will NOT tighten them that tight. Makes me very nervous! However, some do, and I have heard of no problems reported. It is YOUR CHOICE. NOTE also that this is in regards to the 11 mm bolts, and applies to 1981+ models....certainly not the smaller /5 and very early /6 10 mm bolts; which need replacement upon each use, which the 11 mm do not unless damaged, and those early 10 mm bolts on the /5 and early /6 are absolutely not to be torqued to such high values. There have been a lot of different specifications on flywheel bolts over the years. There were two lengths of 10 mm bolts used.
I use, clean and dry, torques of 42-45 foot-pounds on the 1973 and earlier engines; and for the 1974 I use 52-55 ftlbs; and 1975 and later up to the 1981 models, I use about 75 to 80 ftlbs. I use about 80 ftlbs, clean and dry threads, on 1981+.
and, clutch cable problems
32-73-2-324-956 cable is 1460 or 1495 mm long and the sheath is 1285 mm long. This cable may have
32-73-2-324-958 cable is 1385 mm long, and the sheath portion is 1155 mm long
32-73-2-324-959 cable was used on R65 Euro, 86+RS is 1386 mm long
32-73-1-230-041 cable is 1320 mm long, and the sheath portion is 1085 mm long
32-73-1-230-042 cable is 1460 mm long, and the sheath portion is 1225 mm long
3273959 is 1361 mm long, sheath is 1130. Needs confirmation. Believe was on R45/R65
3273694 is 1469 with 1242 sheath, needs confirmation, believe was used on R45/R65 with high bars.
32-73-2-324-960 is 1625 mm and is on K1100LT
3273957 is 1410 long, sheath 1180, used on R80, R100, Mystic
I have a LOT MORE information on various clutch cables, used with various bars, etc. The above may not be 100% accurate now.
See www.siebenrock.com for more control cable information
Clutch cables often?....see below, under
NOTE: BMW clutch cables are lined with a plastic material. DO NOT OIL THEM. The ONE exception was the earliest /5 bikes, which came from the factory withOUT the nylon-like internal lining. I suspect only a few low mileage /5 bikes are around these days with those cables. Aftermarket cables generally do NOT hold up, as they do not have such a lining.
BMW's cable suppliers have sometimes done a lousy job. Some BMW replacement cable barrels do not rotate smoothly...you should file them so they do. A more nasty problem is the top (at bars) crimped portion that do not fit the lever slot properly, and there can be interference and the cable will foul on the lever. BE SURE TO FIX THAT; use a fine not coarse file. Another problem (reported to me) has been MISMARKED CABLES....wrong lengths.
FIRST be sure the cable is routed properly, and tied down only once at the frame. That tie, which must be only barely moderately tight, should be located roughly midway down the right side frame down-tube. There must be no broken cable strands. The clutch lever at the bars should not have excessive UP and DOWN play, and if it does, the nylon bushing IN THE BARS LEVER AREA needs replacing; and make sure the waverly washer IS in the lever depression area for it. BE SURE that with lever movement in any direction (in-out, up-down) the inner cable strands are NOT being rubbed against by the clutch lever slot. Be SURE the barrel rotates easily... lubricate the barrel and the transmission ends with moly grease.
The adjustment is not supposed to be exactly the same on all models. In practice, the new method will work OK for all Airhead Clutches. I prefer to use the old adjustment method for the early clutch. Thus, my recommendations are below:
For pre-1981 clutches (some few 1980 had the later clutch with carrier):
The adjustment at the lever at the back of the transmission sets the free-play clearance at the BARS lever; and the adjustment of the outer cable sheath at the BARS lever sets the adjustment at the lever at the back of the transmission. You want to end up with about 3 mm free play at the bars lever JUNCTION, that is, the outer angle of the lever to casting assembly. Shown in your owners booklet. When the bars lever is half-way through its actual pressure range, the clutch lever at the rear of the transmission should be PARALLEL with the transmission rear case. When you are done you should ALSO have APPROXIMATELY 2 mm of free play at the lever at the transmission rear cover.
2. For the 1981+ clutches the adjustments are done a bit differently. The difference is that the distance measured from the forward surface end of the barrel in the fork of the transmission-located lever, to transmission case where the cable comes through, should be 201 mm. There are also factory books that say 201 to 203 mm. BMW was never really clear on what part of that barrel the measurement was to be from...rear edge? middle? forward edge. The sketches were not clear. I typically just use the forward part of the barrel. The TOP cable adjustment...yes, at the BARS, sets that 201 mm distance.
The next adjustment is the bolt and its locking nut in the lever at the transmission. Adjust for 3 mm of free play at the bars lever. If you do not know how to do this: Loosen the adjustment at the transmission lever a fair amount. You can now move the handlebars lever easily, and if moved far enough, you meet goodly resistance from the clutch. The amount of 'easy' movement, with NO clutch action, is to be such that the lever opening is 3 mm.
When the bars lever is not being touched, the transmission lever will be approximately 4° leaning AFT of the transmission rear cover. You may want to make a simple tool from a piece of coathanger marked for 201 mm, or? to check that 201 mm. Some use a machinist's small scale. Don't worry about the 4°, just know that with #1 eyeball on the transmission lever, it IS to be slightly rear leaning.
Do these adjustments with the engine COOL. Make a tool out of a coat hangar or whatever, mark it "201mm tool for setting clutch lever at transmission". Almost anything will do here. Some have gotten fancy and made a tool that fits over the end of the barrel in the transmission lever fork.
The reason the clutch levers are set this way is to ensure that the
transmission lever operates in the most efficient leverage position.
Now and then someone will complain that their
bike, after sitting, often for weeks or more, often in high
humidity areas, has a clutch that has failed.
You can pull the lever back, it feels normal, but the
clutch will not release, and if you put the engine crashingly into
gear, the engine stalls.
The problem is that the clutch disc has frozen to the adjacent parts. You need to force the clutch to disengage. There are several methods, including pushing the bike, and shifting into second gear....etc.
I prefer to try the following things first (it can take two or three tries!):
(1) Garage try: put the bike on the center-stand, and SECURELY jack the bike at the rear frame crossover
(swing arm area?), ....and have the rear wheel a bit off the surface. HOLD the front
brake! Start the engine in first gear. Do not touch the clutch lever. At some moderate rpm, suddenly
give very hard pressure with your right foot on the rear brake. That may force the clutch to release.
Try twice. If no help, go to step (2):
(2) Warm up the engine, so it starts easily. Push the bike to the street. Start the bike in
FIRST GEAR (depending on model, you may have to pull in the clutch lever at the bars to
allow the starter motor to crank the engine to restart the bike). Ride the bike down the street at
5000 or more rpm in first gear. At a convenient & safe time, suddenly pull in the clutch lever at
the bars & hit the front and rear brakes VERY HARD. Try this up to three times if it
does not let the clutch release immediately. If no luck at all, you will have to remove the
transmission, & work on the clutch.
01/26/2008: all prior revisions incorporated, and much added from old obsolete engineinternals.htm
05/04/2008: Edit section on the plastic throwout bearing piston problems.
04/16/2009: Clarify a few details. Re-arrange order of presentation of items.
10/27/2009: Clarify a few things, fix and add hyperlinks.
11/04/2009: A few additional clarifications on R65/R45 clutch bolts; and re-arrange article somewhat, it
was excessively gaudy.
06/24/2010: Clean up article some
04/29/2011: Add more information, such as a link to the factory clutch tools picture on this site, etc. NO
errors found. Strictly a clarification revision.
06/16/2011: Add Stuck Clutch section, minor other clarifications, quite minor
09/08/2011: Fix typo in part number for the early eighties heavy-duty diaphragm spring; was 2121338508,
should be 21211338508.
10/02/2011: minor clarifications (which I forgot to upload for months)
03/28/2012: add note and hyperlink to my tools article.
04/08/2012: Very minor clarifications on throw-out bearings.
06/08/2012: Completely re-do the clutch levers adjustment area for clarity; clean up excessive use of
fonts, colors, emphasis.
06/25/2012: Expand upon stuck clutch information
06/28/2012: Clarify cable problems and clutch adjustment.
09/04/2012: Add section on setting flywheel and crankshaft to correct alignment. Add QR code; change
Google ads arrangement; add language button.
12/12/2012: Remove end play adjustment details, as is now in the flywheel removal article, 60-2
12/24/2012: Add paragraph on clutch wear dimensions.
04/28/2013: Clarify a few details, remove some redundancies, clean up article, add hyperlink to the
disc alignment tool pdf.
05/16/2013: Expand the section on throwout bearing parts, adding emphasis and an update due to a
bad late style in a R100R that was reported.
08/15/2014: Correct item 3 from CW to CCW; correct flywheel number from -906 to -966
03/17/2015: make sure hyperlinks work properly
© Copyright, 2014, R. Fleischer
Return to Technical Articles LIST Page
Return to HomePage