After my hopeless eff-up of a clutch job, I put nearly 1,600 miles on, slowly looking to the hope that time and wear would rescue me from my own lack of mechanical skill. At a certain point, I simply resolved to replace the entire clutch pack, regardless of time, expense, or aggravation. While I was at it, my last set of Michelin Macadams were at the end of their life, so they would have to go, as well.
I hadn’t come down so long a road with this bike to pull up one step short of mechanical perfection. There had been a long list of defects and faults that had been painstakingly excised, and I could see the end of the road from here.
So I went to my computer, and sourced the parts that would be required to get this project home. A new set of Michelin Pilot Activs, in the stock inch sizes. Matching Michelin airstop tubes. Beemer Boneyard had a new Siebenrock Basic Plus organic clutch friction plate which used a lightened carrier – like those BMW had adopted for its newer twins – combined with an improved friction compound that was supposed to offer higher torque transmission and longer wear. The lightened carrier should be good for a slight reduction of rotational inertia, and a faster revving engine, as well. Then I obtained a new heavy duty diaphragm spring, pressure plate, pressure ring and clutch bolts from a BMW dealer.
Now it was time to wait for the UPS man, and then try to clear enough time in my calendar to bring the entire job finally home.
Coming up to one weekend, the weather report absolutely sucked.
Now normally, weekends are time for camping trips, for yardwork, for trips to the C&O Canal Towpath, for motorcycle rides – for enjoying the beautiful outdoors that my Central Maryland home provides in abundance. Don’t misunderstand me, I’ve been riding motorcycles and bicycles in the rain, I’ve taken canoe trips in the rain, I’ve done more camping in the rain (and some in the snow!) than I’d really care to recall, and I’d be the first to admit that nature also has beauty in abundance when it’s raining, too.
But nature also provides cycling jerseys with brown stripes of mud up the back, cold sodden socks and boots, and sleeping bags with little yacht racing courses magically hidden within.
So it’s one thing to already be in the outdoors, and deal with what Mother provides with grace and cheer. It’s all together another thing to head out when it’s already a Beautiful Day To Be a Duck. And it looked like we had several of those days on tap.
So, given the plethora of other things we would not prefer to do in the rain, it looked like I had the time I would require to unwind my own dumnisnitude, and could tear into this bike for what one could only hope would be the last time for a while. And on the bright side, the fact that I had done this fairly recently, meant my knowledge was fresh and that some little procedural tricks to smooth the way were firmly in mind and readily at hand.
Finally, I did something that I’ve been thinking about for a great while, but had never done. I’d experimented with some disposable nitrile gloves when performing work like this. My experience was that most nitrile gloves had a life expectancy of about 25 minutes in this kind of use. My various bike supply catalogs had been pitching Mechanix brand gloves for years, so I went down to my local auto parts emporium – where everyone knows my name – and dropped $15 bucks on a pair. I do not regret that decision at all – coming inside after removing and replacing a transmission without reeking of sulfurous gear oil, with no dirt and oil under my nails and no cuts and bruises on my hands was a revelation. Although I’ll admit there may have been one or two places where a very slight reduction in dexterity was apparent, these gloves will be part of my mechanic kit from now on.
Out in the garage the drill was revisited. Tank and seat removed. Airbox, manifolds and battery out. Clutch throwout and cables removed, swingarm pivots out, driveshaft unbolted. Gearbox mount points undone, neutral light switch disconnected, and gearbox rolled out the left side of the frame.
Sounds simple, right? Wouldst that I could do it as fast as I can describe it.
I got my boxes full of new stuff from my suppliers and laid the parts out on a plastic sheet that had enclosed the new pressure plate during shipment. Stuff was laid down beside the bike in order, because, well, visualization helps.
So on my floor we had the diaphragm spring, pressure plate, Siebenrock clutch plate, pressure ring and six fillister head bolts.
I also got the drawer out of my rather massive hardware organizer system on my workbench that contained the secret sauce for this job – my clutch tool kit. Six overlength bolts, nuts, washers and the Ed Korn centering arbor.
The old clutch came out easily – the six bolts were easy to remove against the spring tension, and the parts came right out when the last bolt came free.
My curiosity, of course, wanted a detailed examination of the friction plate and pressure ring. All things considered, it didn’t look that bad, but there were traces of where the moly grease had walked to the outside of the friction disk, and clear signs of local spot overheating and slippage on the matching pressure surfaces. It wasn’t bad, but it was bad enough. Suffice it to say a little moly goes a very long way.
I don’t own a micrometer, so I can’t tell if the old clutch was already under the minimum thickness spec. It would be great if it was, because then I would only feel about 38% as stupid as I currently felt for having had to do this job twice. I have kept the disk on my workbench, though. Next time I visit someone that I know owns one, you can bet I’m going to measure that friction plate.
Knowledge is power. This ain’t over till it’s over.
In one of BMW’s airhead boxer motors, installation of a new clutch pack is trivial if you have the tools and you’ve already removed the transmission. I placed the diaphragm spring into the recess in the flywheel and laid the pressure plate on top of it. The Siebenrock friction disk went into the middle and then the pressure ring closed the whole affair up. I ran three of the overlength bolts into their tapped holes in the flywheel, placed the centering arbor into the clutch splines, and then began running the bolts down to compress the pack against the spring tension. Once the spring was mostly compressed I started three of the short clutch bolts and then went around in a star pattern tightening everything up until the pressure ring was in full contact with the flywheel.
Then I removed the overlength bolts one at a time and replaced them with the other three clutch bolts. One all six were in place, I went around the horn and tightened everything to the final torque specification.
Now the whole teardown needed to run in reverse.
First the gearbox goes back in place, and the bolts that hold it are hand tightened. Then there is the most finicky part of the job – getting the driveshaft bolts back into place and retorqued.
This is a tiny minefield – one has to operate in the 1 5/8 inch available between the driveshaft boot and the rear of the transmission. If, heavens forfend, you should bobble and drop one of these bolts, it will very likely disappear down into the bottom of the driveshaft housing.
How I know this is something of which we shall never speak of again.
Except perhaps to say that if one were to have one of those powerful, tiny telescoping magnets that one sometimes sees in tool stores, it would be worth any amount of money at such a time and would be capable of transmuting deepest despair into the purest most unalloyed joy.
Remember, though, we shall not speak of this.
I was able, this time, to avoid such horrors, and got all four bolts threaded back up onto their holes in the output flange. To tighten these bolt back to spec, though, one has to relocate the swingarm up into position and reinstall the pivot pins, as one needs the resistance of the wheel and rear brake to push against.
My endurance is not what it used to be, I guess, because at about this time my ability to form usefully coherent thoughts and do bench presses with rear wheel and swingarm assemblies began to decline precipitously.
Dinner, blood sugar, beer and sleep seemed to be much better ideas than pushing forward though fatigue. I’d done one major dumbness pressing forward under such conditions recently, and was determined to keep my Dumb-o-meter pegged at ‘1’.
That night, my brain continued to mess with me in my sleep while it showed eyeball movies of scissors jacks and prybars dancing with swingarm pivots.
The next morning, though, with said brain actually supplied with energy and working, mental connections were far easier to complete.
After standing in front of the bike for all of about three minutes, the dim recollection of the rear brake trick flickered in my brain, and I hooked up the rear brake rod, stood on the pedal and watched everything line back up.
30 minutes later, the whole bike was back together. I fired the motor briefly to center the transmission, and then tightened up the 4 transmission mounting bolts.
I spent a few minutes checking my work, and as I was adjusting the free play on the clutch mechanism, the sun came out outside the garage.
Meteorology, to say the least, is an inexact science.
I pulled on a Bell 500 open face helmet I keep lying around for these little short distance test blasts, warmed the bike and went up and down the street in front of the house a few times. The clutch engagement felt great – soft, smooth engagement and clean disengagement. I stopped in the end of my driveway and checked the clutch free play again and did a final visual inspection.
I refired the motor and gently trolled though my neighborhood. If anything, with a clutch that actually worked properly, Mark’s gearbox seemed even more precise. I slowed down by the park at the other end of the neighborhood, dropped to first gear, and stopped. I engaged the clutch again and started smoothly – then I rolled the throttle open.
The bars went light in my hands as the ‘thock’ of the fork’s top out stops rang out. Clearly we had entered the ‘zero driveline slippage zone’. I gave the throttle back and headed for the entrance to the highway with a big, evil grin on my face.
I only ran about 15 miles on the checkride, but it was quite clear that the R90S had been restored to its former feisty glory. The bike pulled hard from low rpms, and all of the top end was back, too. Shifting around 5500-6000 rpms revealed a gearbox that was nothing less than spot on perfect. My 2000 K bike does not shift this positively.
I ran down St. Marks Road, a pretty typical one lane country road that follows the bed of Catoctin Creek, and finally got to enjoy the sensation of steering with the throttle again, rolling off on the way in and back on on the way out. Over little rises with the gas dialed on she’d lift the front wheel.
Might I have gotten a little verklempt inside that Bell 500? It was probably just the wind leaking around my glasses.
Since I wasn’t in anything like full gear, I headed back to the garage to clean up the debris from the major tear down, so that I could regain use of my garage.