As you requested, here is the BMW clutch article. Sorry about the typos; this was a quick scan job. -------- Smoother Shifting for BMW Twins from Motorcyclist, December 1992 Precision gear BY ARMEN AMIRIAN BMW twins have earned a lot of praise for a lot of reasons over the years, but rarely for their shifting. Get off the average Bavarian beast and onto any Japanese bike built in the last decade or so, and the difference is usually quite dramatic. The underwhelming shifting abilities of the Bavarian boxers leave much room for improvement. There are a few different avenues of approach to the problem of poor shift- ing on BMW twins. First, the clutch externals must be in good shape and properly lubricated, something the average owner can see to. Second, the input shaft must be clean and properly lubricated and the clutch parts in good working order. This should be handled by someone with a bit more mechanical ability and access to a few special tools. And finally, the shimming of the transmission must be perfect and the shifter upgraded, where applicable. This third step requires fairly serious tools and abilities and should not be undertaken by the average shade-tree mechanic. SIMPLE STUFF Start by making sure th,e clutch cable and the rest of the extemal mechani- cal bits are in good order. Early models used an unlined clutch cable while the /6 and later models used a nylonlined affair. Slide the dust cover off the bottom end of the cable (on the lower right side of the transmission) and take a look. The nylon lining will be visible here; if there is none, consider swapping your old cable to a newer, lined one. The unlined cables like to be lubed while the Teflon ones would rather be left alone. Remove the clutch lever and clean and grease the pivot pin, the pivoting end of the cable and the part of the lever that rubs the housing. Up until 1980, the cable arm on the back of the transmission had a grease fitting on it and some of the gearshift assemblies had grease fittings on their linkages as wellÑgive them a shot with the grease gun. The early ('78 to '82) shift linkage used a bent rod to connect the shift lever to the transmission shift shaft; take a few minutes to upgrade to late-model Heim (Rose) joints with spherical ball ends. Be sure to follow the factory clutchadjustment procedure. There was a dramatic change for '81 and later models; check your shop manual. Every few years, from /2 to /5, from /5 to /6 and with the R65 in 1979, BMW reduced the weight of the flywheel slightly. Finally in 1981, the clutches and flywheels of all models were radically redesigned and light- ened to the point where the flywheel was renamed the clutch carrier. If your bike is a pre-1981, shifting will be improved and the bike made easier to rev if the flywheel is lightened (unless you have an R65, whose flywheel has always been light). NOT SO SIMPLE STUFF Probably the most common complaint with the shifting is the abruptness of the clutch engagement (my /5 was so bad I would engage first gear, point the bike in the desired trajectory, release the clutch and launch the bike). For years unknowing types have dismissed this as a fault typical of a dry clutch, all the while driving cars with a dry clutch and smooth clutch engagement. Actually, the two most common causes of clutch-engagement abruptness are incorrectly shimmed transmission shafts and dry input-shaft splines. The drive (primary) gear on the input shaft is a helical gear. As the clutch is released and power is fed through the gearbox, a load is placed on the shaft. If the shaft has excessive end play, it will tend to shift under load. As the clutch rides on the end of the input shaft, the movement of the shaft affects the clutch's engagement. The result is the clutch engaging and forcing the input shaft back into the transmission case with a loud bang. If this is allowed to go on long enough, the transmission bearing on the end of the input shaft will be bashed into early re- tirement (as I found out 500 miles from home in the Blue Ridge Mountains). Dismembering and shimming the tranny requires quite a few special tools and a bit of expertise and is best left for the pros. BMW now recommends that the input-shaft splines be cleaned and lubed once a year or every 10,000 miles. The splines run dry and are subject to rust, but even worse is the tendency for clutch dust to fall off the clutch disc and land on the splines, coating them with an abrasive powder. As the clutch disc slides back and forth, the splines are worn away until one day engaging the clutch only yields a loud grinding noise. There are many wrong ways to do the job and only one right way. You must pull out the transmission, clean the male splines on the transmission as well as the female splines on the clutch, lube correctly and reassemble. If you merely move the trans back and goop the splines, you are likely cover- ing up the abrasive clutch dust and rust particles with the new grease. One local dealer merely slid the trans back and gave the input shaft a shot of WD-40. Needless to say, the bike was back in the shop in short order. It is imperative when lubing the input shaft not to place any lubricant on the female splines of the clutch disc. If the female splines are lubed, the grease will be pushed off the splines as the transmission is inserted. Once the bike is fired up, the grease will be thrown onto the clutch disc, causing the disc to stick to the pressure plate. Many moons ago, BMW suggested using an antiseize with high moly content on the splines. After further research the company switched its rec- ommendation to a special lubricant named Staburag (part 07-55-9056992). This stuff looks like very sticky grease and is apparently The Business: a small tube costs over $18. Those faint of wallet will probably opt for aftermarket antiseize, but the new lube really is better. Either way, only a thin film of lubricant is required. Any excess will be pushed off the splines and find its way onto the clutch disc. TROUBLESHOOTING Sometimes balky shifting (especially downshifting) can be traced to a sticky clutch disc. To determine if this is your problem, place the bike on its centerstand with the rear wheel clear of the ground and start it up. Pull in the clutch, put the bike in gear and apply the rear brake. If there is a violent shock or shudder, it's likely the clutch disc is sticking. This might be due to the pressure plates rusting after the bike has been sitting for a while. This is not a problem. However, if the clutch sticks every morning, it is probably because the disc is contaminated. The only solution is to disassemble and replace the disc. There were some bad clutch discs used by the factory in the early '80s which tended to stick and wear prematurely. Any new discs are of an improved material. The four-speed boxes used until the end of the /5 series required quite a bit of finesse to set up properly. Location of shift forks, end play of shafts and overshift of the lever in both directions were all adjustable. Not only is this setup not a job for the amateur, it is not a job for just any dealer. You must find someone who has worked on and specializes in the older machines. On the five-speed boxes, only the end play of the transmissions can be set. If there is excessive play in the shafts, there may be noticeable grab during clutch engagement. The only accurate way to measure end play is to pull the rear cover. The quick and dirty way is to warm up the transmis- sion housing around the appropriate bearings and pull the shaft in and out, feeling for excessive play. This only works for the input and output shaft, not the countershaft, which does not protrude through the case. Although all BMW boxers require a long and deliberate shift to engage the next gear positively, some are worse than others. If any of the three shafts are shimmed too tight, they will not spin as freely, causing stiffer shifting. In 1981, when the R80GS was introduced, BMW must have realized that an on-and-off-road bike with a lazy shifter was not the hot tip. A new shiftselector mechanism was incorporated, with noticeably sharper ramps for the shift detent. With the new setup, the shift detent either snapped into the next gear or rolled back into the gear previously engaged, theoretically eliminating the old bugaboo of false neutrals. In 1982, the improved shifter was incorporated into all of the models. Further good news is that the upgraded shifter system is now offered as a kit (part 23-31-90560150) for only $65 and can be installed in any five- speed box. The only note is that the later (post-'76) neutral switch must be retrofitted if the kit is used on '74 to '76 /6 boxes. It should be pointed out that the new shift kits require slightly more shift-lever pressure to change gears. Most riders will see this as a small price to pay for crisper shifting. Although no changes are made to gear shafts and shimming should not be disturbed, it is advisable to check these areas anyway. At the risk of sounding sacrilegious, boxers were rarely perfectly set up from the factory, but this seems to be improving. BMW has flopped back and forth over the years about the method of sealing the rear cover. For a long time a gasket was used, and then the factory eliminated the gasket and used Hylomar, the blue Rolls-Royce-approved sealant. Now it appears the gaskets are again in vogue; sometimes the shafts have insufficient end play when the sealant is used. Using a cover gasket lifts up the cover enough to give end play for the shafts. While the gearbox cover is off, the tube on which two of the shift forks ride can be removed merely by tugging on it (with perhaps a bit of heat applied to the front of the gearbox). Careful polishing of the shift-fork tube and detents makes for smoother shifting. --------------------------------------------- Armen Amirian has been a head mechanic at a BMW shop and a teacher at City University of New York Technical College (he taught motorcycle maintenance for 12 years) and is a frequent contributor to several intemational magazines.