Clutch
Pushrod, throwout bearing, lever at rear of transmission, cables, clutch carrier/flywheel, bolts, ETC.

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clutch.htm
Article 60, subsection 9

 Crankshaft end play, spacers, ETC: 

Fairly rarely; and, after huge mileages usually (but NOT always) one sees an Airhead that has two or more of the following symptoms:   Shifts hard (and isn't lack of input shaft lubricant or bad clutch); most probably has a lurching, grabby clutch action; idle rpm is unstable and varies with clutch pull-in; engine vibration.   If you have an airhead with those symptoms, you may want to check the end-float (end play) of the crankshaft. This is a serious subject.  You are advised to see an expert, or to get the BMW official information, but here are some things that may clear things up a bit.  This is the arrangement you might typically expect to see if you removed the crankshaft and viewing the crankshaft in the engine casting from the crankshaft rear end:  

FIRST you have a GREEN thrust spacer which is .1015-.1034 in thickness; next is the main bearing insert, next is the RED thrust spacer which is .0978-.0996, then the oil seal, then the flywheel.   This is for a 1970-1978.  In 1979 BMW added the O-ring seal and the flywheel changed design a bit.  If you have a BLUE thrust spacer it is .0996-.1015" thick; and a YELLOW is .1034-.1052.   The limit of wear is .008" and end float is .003"-.006". 

Warning!!.....Warning!!.....Warning!!!
Many times a combination of clutch, main seal work and replacing the oil pump seal is done all at the same time.  To replace a main seal or oil pump seal, you HAVE TO remove the clutch and the flywheel (called Clutch Carrier from 1981).  Under NO circumstances must the flywheel be removed without blocking the crankshaft!   See article flywheelremovalwarning.htm

Not only must you block the crankshaft, but be sure the OT mark is in the timing window when removing and replacing the flywheel (or clutch carrier).    Do this "removing and replacing" ONLY when the pistons are fully extended outwards.  When the flywheel is showing the OT mark in the timing hole, the pistons are to be fully extended outward.  If that is not seen, then the flywheel is mounted to the wrong crankshaft bolt holes.   Many a person has goofed, so, forewarned, you won't, right?  The flywheel is not 'indexed' and can be installed to the wrong crankshaft holes.  Furthermore, the flywheel is to be centered CW/CCW in its holes, before fully being tightened.

Since it is a MUST to mechanically block the crankshaft  from moving forward before removing a flywheel, 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 and 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 outer timing chest cover.  Usually 3/4 inch overall.  The length should be such that some light pressure is applied by the cover, the cover being screwed back onto the engine, but the cover can't quite fully fit home all the way.  A further treatment of how to make this tool is in the TOOLS article on THIS website.  (that is a hyperlink).    FURTHER, there is a sketch with information; on this website, so you can REALLY see what is going on......SEE, without fail:      flywheelremovalwarning.htm
That article has hyperlinks to the needed tool, and lots more information.  >>>>READ IT!!!<<<<

Clutch parts, including flywheel, should be identified by marking with paint or punch pricks before you disassemble. BMW did that on some models.  Parts are generally installed at 120°.   This confuses folks, so pay attention:  In case those marks are not seen, 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....NOT lined up!  YOU can make YOUR markings with arrows, if you like, for the markings TO BE lined up.  YOUR CHOICE.   When I personally do a clutch job, I make punch prick marks.

/5 clutches had changes during and after production.   The replacement diaphragm springs were changed, and 6 spacers were no longer used.   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 thing, 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.

HINT!.....The early R65 and R45 had smaller clutches than the larger engines did.  The amount to torque the clutch bolts to the flywheel is hard to find, including in BMW's own literature.   In fact, there is some confusion over this.  BMW originally had Allen head bolts, then later went to hex head bolts.   Some published figures are as high as 17 footpounds for the bolts.  That is likely 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.   

BMW made a big change to the clutch/flywheel parts in 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, so shifting was easier; but engine vibration generally increased.   The 1981  clutch parts (as opposed to later clutch parts) were sometimes very troublesome, and some nasty failures were seen now and then.    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 on 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 21-21-1-242-353, and a higher pressure one IS available, as 21-21-338-508.   There were other updates.  The pressure plate 21-21-1-242-354 became 21-21-1-243-009, which became 21-21-2-302-200.   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 21-21-1-338-680.   If you are overhauling a 1981 model, it is a VERY good idea to replace all the parts that were updated...which is nearly everything!

Note that late production discs have no asbestos, and may not grip quite as well, and if you replace just a disc, if the mating parts are worn some, they may well not be dead flat, and 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 then recommend checking the taper/flatness of the parts.  Use of new parts will guarantee a proper, and strong, clutch, but the set of parts is not cheap.   The heavy duty higher pressure spring is a good idea, especially with these later non-asbestos discs.

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.

NOTE:  The throwout bearing, of which there are two basic types, need to be removed and cleaned and lubricated now and then.  Failure to do this can result in not only poor clutch operation but on one version a disintegration of the bearing and having broken parts get into the transmission and doing damage!

HINT!!!.....exceptionally stiff clutch action can be due to worn and grungy and even broken parts in the clutch throwout bearing area, including the bearing, piston, etc.    Do NOT forget 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.  Be SURE to grease the bar lever area (not the pivot there, it is nylon lined), and be SURE that the cable inner strands are NOT fouled by the slot in the bar lever!!  It is especially important that the cable end, called a cable barrel, be free to rotate in the clutch lever.   Pulling the clutch lever slowly backwards will show if the barrel is moving freely.  If not, unfasten the cable from the lever, and clean up any rough spots on the barrel, then reinstall using a moly grease on the barrel.

Slipping clutch?  Acts up when engine fully heated up?...etc...??

On later models, the plastic 'piston' 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 when hot.  The throwout piston part is next to the 1 inch mark of the ruler in the photo below.     The LIMIT is 28.7 mm, and it can be sanded down, or replaced (read the NOTE! below!).  This occurred because tolerances on some transmissions throwout area bore sizes, and these throwout pistons were not held tight enough.  This is from 1981, when BMW changed the clutch design radically.    If the piston fits into the bore a bit too tightly...(it may still operate smooth enough when cold), under some circumstances, PARTICULARLY when HOT, the piston may stick.  That is because that plastic piston material expands a lot faster than the aluminum bore it fits into.  Obviously this means that a proper check is with a hot transmission!    This can manifest itself in several ways, INcluding a seemingly 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!!).  I can't give a hard and fast rule here, but if yours 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.  You might want to check the fit, hot, if you have any hot clutch slipping problems, but OK when cold.   Whilst this 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.   Use a micrometer or vernier caliper to measure the piston diameter.   Inspect the bearing, and if it looks bad, replace it.  Grease it with a good grease (Do NOT use moly).    While the bearing is theoretically lubricated by oil from the transmission, that is not hardly so at initial assembly....so use a soft mild grease, non-moly.

>>>BMW has had three versions of the unit, and offers a replacement piston:  23-13-1-464-167, another way of coping with a sticky hot piston....and if your bearing is shot, you can consider that pricey part, as it is a new design, and incorporates the bearing, and it has the proper diameter.  You really do NOT have to spend the bucks....you can sand yours.  NOTE!....it has been reported to me that BMW is now shipping an all-plastic part that has the same old problems!....so, be sure that no matter what part you have in YOUR bike, that it is not expanding and seizing up!

Below is a picture of a 1982 felt-less clutch rod, 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.

NOTE!.....the bearing is lubricated with transmission oil during operation; but that takes time and miles...so....  I always use a very light grease when installing this bearing.  NOTE ALSO that the "felt-less' clutch rods came into being 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 inserted from the FRONT of the transmission.  It is possible from the rear, with a homemade tool, but I recommend against it.  

The felt IS necessary on models prior to 1981, otherwise the clutch disc can become oiled and thereby slip, and be ruined eventually. 

The 1981 and later models have a lipped seal, not easily replaced....the transmission must come apart.

  HINT!...PAY ATTENTION HERE!!....

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 reliable.  

Then, the later 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 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.   A cure is to remove the old pin and clip and install the following parts:
#23-13-1-241-484  pin, that has a flange, and won't fly out.   This is used with a clip that is part number  51-23-1-864-963. 
 

   _{Another HINT!.....
     BMW came out with a Service Information bulletin (we call them SI's) in November 1991, this SI is 11-049-91, #2495, and this can also be seen on the 12/92 fiche on page 3, G23.    Basically, it stated that whilst the flywheel bolts were previously at 75 footpounds (100 Nm), they were now to be at 90 footpounds (125 Nm), and cleaned threads, and 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!.  NOTE also that this is in regards to the 11 mm bolts, and applies to 1981+ models....certainly not the smaller /5 bolts; and, frankly, I won't do ANY years of airheads to 90 footpounds!   There have been a lot of different specifications on flywheel bolts over the years.}   

_{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, clutch action is poor, and shifting can be stiff and poor.   Never lube the disc spline, just the INPUT spline.   Cleaning and re-lubrication should be done at a mileage and time commensurate with your driving habits and atmospheric conditions.   Moisture condenses on the shaft and the in-out movement during operation of the clutch 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; especially so on pre-nickel plated ones.   I suggest a look and C/L at/of the 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.}

EZ-Clutch:  The pre-1981 clutches have a heavier pull at the bars, some dislike that, or cannot easily cope with it.  There are several types of modifications to fix it, besides the HUGE expense of installing a 1981+ clutch.   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 USA;   www.benchmarkworks.com   They also have it available from a 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
There is another type, can't remember the URL for the website.

There is a factory tool to help line up the disc.  You don't have to have one, eyeball is good enough.  If you want to make this tool:  

There is a photo of this type of tool in the tools.htm article

Flywheels, clutches, and their bolts: 

1981 and later bikes used Clutch Carriers, NOT officially called flywheels, and the information below on the 11.5 bolts torque is correct for these.

***NOTE!!!...critical: see prior cautions on blocking the crankshaft!

NOTE!:  the 1979 and 1980 R65 models used a 6 x 1.0 mm clutch bolt.  The proper torque, per Tom Cutter, is 88 INCHpounds.  That is 7.33 footpounds.    The larger displacement models have larger bolts and are 17 footpounds up to 1980, then the clutch cover-to-carrier is 15 footpounds.

  All 11.5 mm bolts:   The original good specification was:   Torque these to 73 ftlbs.    Threads must be clean, dry, NO Loctite used.   SEE just below: ****

Cables: 
32-73-2-324-956 cable is 1460 or 1495 mm long and the sheath is 1285 mm long.  This cable may have been 32-72-1-235-744???
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

See www.siebenrock.com for more control cable information

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

Rev:
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.