Failure of the output shaft seal (rear main seal as we referred to it in my early studies of the mysteries of machinery) or of the shaft O-ring and the accompanying oil leak into the intermediate housing (we called it a bell housing) contribute to a significant number of BMW K1200RS/GT/LT motorcycle clutch failures. Clutch slippage on these bikes is more of an "it shall happen" than an "it might happen" problem, though there are a couple of "ifs" that lead to problems. "If" the output shaft seal/O-ring doesn't give up the ghost first, leakage from the hydraulic clutch slave mounted on the rear side of the transmission will likely take the clutch out for a spin. Instead of oil leaking past the main seal and into the intermediate housing where it contaminates the fiber clutch plate, hydraulic fluid pools in the slave cylinder cavity then, with no other escape path, fluid works its way along the clutch activation rod and into the intermediate housing.
Even a relatively small amount of lubricant or hydraulic fluid will impair the ability of the KRS and KGT single, dry clutch plate to provide linkage between the engine and transmission. The only remedy for clutch slippage is replacement of the offending disk. The task of replacing the plate, while not overwhelmingly difficult, is time consuming, tedious, and somewhat expensive. While satisfying once the task is completed, it's a procedure few of us care to repeat very often. Even if no seepage is detected at the clutch slave when the unit is accessed, many owners choose to replace this unit (about $150 or so) at the same time as output shaft seal and O-ring are renewed or vice-versa. Even if there's no visual indication of leakage, a variety of seals on the transmission might also be replaced at this time.
This electronic journal encompasses my personal tao while removing and replacing the final drive train of my 1998 BMW K1200RS. Procedures should be similar for any of the 1997 through 2005 K1200 series motorcycles, including the 1200LT (light truck) series. The experience I shall describe includes raising the frame, removing the drive train and replacing the dry clutch disk, output shaft seal, shaft O-ring, and clutch slave cylinder. It does not deal with disassembly of the transmission, final drive, or replacement of the transmission shaft seals. Also, I left out any description of removing the fairing and sundry small bits. If one isn't comfortable with taking off the fairing, fuel tank, etc., one probably might want to hesitate before embarking on a drive-train disassembly. Much like entering a marathon, if one fears running a kilometer, twenty-six miles might be an overwhelming challenge.
The BMW factory K1200RS manual and the Clymer Manual for the BMW 1998-2001 K1200RS are invaluable sources of guidance for the job ahead. I printed applicable sections of the BMW material and kept the pages alongside the Clymer manual in my workshop. Additionally, invaluable information was gleaned from the i-bmw.com site and from the on-line technical forum of BMWMOA. Both of these sites (links in the column to the left) provide contributions by owners and mechanics. Anyone considering replacing clutch and sundry associated parts on a BMW K-bike in their own shop will benefit by becoming familiar with information available from both manuals and the websites. If using i-bmw.com, please consider making a PayPal contribution, the site is free to registered members but it still costs money to maintain. Same for BMWMOA and its site, bmwmoa.org. You can access the forums without joining the club but you'll get better karma (and much better cyclema) if you pony up the cash.
There are other sites and other clubs which also provide information on BMW technical operations. They may be excellent; I just didn't avail myself of their knowledge so I don't refer to them. I also offer caveats to the mechanic about to undertake this particular task. First and foremost, make an honest assessment of your skills, tools and available workspace. Though an "emergency" clutch replacement could undoubtedly be effected using minimal tools under the most onerous surroundings, I would guess most mechanics wouldn't choose to do the job under such conditions unless there were no alternative.
Why consider doing the job at home? BMW K1200RS, etc., clutch replacement is rumored to cost $1500 or more when the work is performed at a dealership or even by an independent mechanic. Depending on which parts are replaced and whether the replacements are new or used, subtract labor costs and the job can be completed for as little as a hundred dollars. This latter figure is a for the bare minimum, a used clutch plate, new output shaft seal and O-ring, and a few other necessary replacement bits and pieces. If one should buy all new parts, the price goes up to $300-$600. Neither of these estimates take into account expenditure for tools, both common and specialized. Choose to purchase all the factory devices for clutch replacement, tag on several hundred more dollars to the final bill. Many people performing this task (including myself) consider most factory tools an optional luxury. In some cases, it's possible to fabricate devices that work as well or even better than what the factory sells. In other cases, the mechanic chooses the "field expediency" method which has its own benefits (lower cost) and pitfalls (possibly the job doesn't get done properly.)
If you should decide to do this work yourself, the results are your responsibility. If you harm yourself, understand this is a possible outcome of attempting such a job without adequate training, tools, workspace, etc. If this possibility bothers you, take the bike to a dealer or independent mechanic. I do not recommend doing this job at home; I merely present the results of my own experience with the task. This description of work performed is purely informational. Even if one choses not do do the job oneself, electing instead to have a dealer/independent shop perform these tasks, one will likely benefit from understanding what is being done to the bike, what can go wrong inside all those housings, what associated parts might need replaced, and, maybe most importantly, why the shop is about to ask for a grand and a half or so when the job is completed.
Even dealers frequently discover that they must wait for parts to arrive before a job can be completed. Independent mechanics seldom stock all the parts available at a dealership, so delays are even more likely. Mechanics preparing for major maintenance at a home-based shop seldom have the luxury of bins of fasteners, seals, gaskets and other parts on hand thus likely will be faced with almost certain downtime while waiting for UPS or the mail person to deliver parts. Take this into consideration when setting up your work area. If you need to access the space frequently, a disassembled motorcycle may create problems.Better to wait while accumulating supplies and finding a block of open time than to partially disassemble the motorcycle while hoping to finish the job some day in the indeterminate future. Many would-be mechanics have discovered this latter technique is the tao of creating a "basket case."
By using on-line schematics, fiches at they were once called, one can determine a number of necessary parts and have them on-hand before beginning disassembly. Start off with parts you know you'll need to replace, such as clutch plate, new bolts and washers for the clutch assembly, output shaft seal and O-ring, center retainer bolt, two fastners for the rear brake disk, new washers for the two clutch slave fluid lines, slave gasket, etc. The list can be quite extensive if one includes all the transmission seals, rubber boots and other parts that might need replaced. I preferred to take a middle of the road choice on accumulating parts before beginning disassembly. I bought what I knew I would have to have and a few parts I might need, accepting that what I didn't use would go into the K-bike parts inventory for future use.
Of course I needed a few parts that I didn't order beforehand and I put more parts, particularly seals, in back-up inventory than I intended. That's how it goes. Next to consider before beginning the job are tools.
Metric socket sets in 1/4" and 3/8" drive, torx sockets, and hex head (Allen) sockets are necessary for this particular job, though they're only a beginning. A mimimalist path seldom works when it comes to tools; at least not in my experience. Each mechanic has personal preferences in what is considered necessary, both in variety and quality, for a well-stocked tool chest. Odd items that shouldn't be overlooked before unbuttoning the BMW for a clutch change include a 12mm hex head socket or a 12mm Allen key (I prefer having both on hand) for the front and real bearing retainers on the rear fork (single-sided swing arm); a 30mm socket for same; and a seal puller.
Most tools are relatively accessible. However, there are a few specialized items that are going to be required before the K-scooter coughs up its slipping clutch disk and others that will be needed to get the pile of parts reassembled. These include a brace bar to keep the clutch basket from turning when removing and replacing the center retention nut; a drift or mandrel to properly insert the new output shaft seal, a method of centering the clutch and pressure plate when reassembling the basket; and either a tool or a technique for locking the rear fork bearings in place while applying high torque to the outer bearing retention nut.
My personal choice was to purchase a disk centering mandrel and a seal insertion device. I fabricated the clutch basket retention strap and used a technique rather than a tool for the rear fork bearings. The choice of which tools to buy is up to the mechanic but the final decision should take into consideration how likely it is that the job can be accomplished safely and correctly. It makes no sense to spend 20 hours working on a motorcycle only to discover the job was done wrong, possibly even causing more damage than existed beforehand.
Also optional is a digital camera. Often photographs provide more of a record for the future than an asset for reassembly. To be of real value, photos should be well-lighted and closely focused on the material in question. Overall shots of the bike carcass are not of much use when attempting to discern which part goes where. Much more important than a camera is a pen, notebook, a pack of string-tie tags (easy to find at Staples or the ilk), a permanent marker and a roll of masking tape to label items that can't be tagged. Notes made of the disassembly sequence are invaluable when putting the bike back together, avoiding those forgotten wire connections or questions about which part has to go on first.
Also necessary for this particular job will be a way to safely anchor the large and heavy motorcycle carcasse while the frame is raised and the drivetrain is removed. Some mechanics prefer a hydraulic table; others a center jack. A small shop jack with wheels is handy to steady the transmission during removal and replacement. Some method is necessary to raise the frame, either an overhead lift (which can be quite simple as the frame is not particularly heavy) or a method to jack the frame from below. The choice of how to do these tasks is an individual matter. After reading the next section of this experiential dialogue, you should have a vague idea of what you'll need to do and how to do it.
Click here to proceed with Step II of the Tao of Clutch Replacement, which details my experience in stripping the bike that the frame might be raised, removal of the drive train, clutch disassembly and replacement of the clutch disk, and reassembly of the machine so it once again is capable of bringing terror upon small Hondas and large Harleys.
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