I just replaced the gear box on my K75 with a spare one that I had loaned to a friend.
We are rebuilding the broken one and soon I will be ready to post all my pictures of the repair.
Just for now, I want to give you a trick to re-attach the gear box on the engine.
The most difficult thing is to keep the clutch plate in line with the output shaft of the engine. I had made a special centering tool for this purpose:



If you don't have the luxury to have a centering tool, go to the closest office supply and buy a "Papermate" permanent felt marker. This will do the trick as the diameters are the same.



When the clutch plate is centered, you don't want to move it when trying to insert the gear box input shaft and the clutch push rod. (If you carry the gear box by hand, you will have to try and recenter many times before it's right).

This morning I had an idea and went to get the longest 8mm bolts that I could find.
The idea was to have some alignment pins to have the gear box sliding on it. At the end, I hade to cut the screws to a length of approximatly 90mm (or 3.5"). With my saw, I also made a slot in order to use a screw driver to remove them when the gear box got in place. I installed the drive shaft on the gear box to turn it and line up the splines of the input shaft/clutch.
It worked well and at the first try I was able to re-engage the gearbox on the clutch.
Here are the pictures of the aligment pins:



This is normally a tricky job, and if you don't succeed at the first time, get a big breath, relax and try again. It could be very frustrating.

Bert

Bert , nice advice, I just went thru the whole thing three times, and one it went like a flash,second time a struggle third time I figured out the pressure plate moves, I have a spare push rod I used to center it by eye but I.'ll go with your way next time, the book did not mention the plate moving and I think many people think that the splines aren't lineing up , but with your method it will be much less trouble, I also found when you take the shafts out of the case, use a heat gun and to put them back , put the shafts in the freezer, as well as heating the case,make's it much better,

nice site,
Brian

yankeeone wrote:Bert , nice advice, I just went thru the whole thing three times, and one it went like a flash,second time a struggle third time I figured out the pressure plate moves, I have a spare push rod I used to center it by eye but I.'ll go with your way next time, the book did not mention the plate moving and I think many people think that the splines aren't lineing up , but with your method it will be much less trouble, I also found when you take the shafts out of the case, use a heat gun and to put them back , put the shafts in the freezer, as well as heating the case,make's it much better,

nice site,
Brian

If you are not affraid to make your wife really mad, put the gearbox casing in the oven. The good thing about the oven is that you can regulate the temperature and have a the whole piece evenly heated. In theory, it will prevent any warping. A heat gun would leave some parts cooler than the others and creates some tension on the casing.

Disclaimer: I am not taking any responsability if your wife beat you with the roller pin when she discovers some bike parts in HER oven and HER freezer.

Talking about the clutch and pressure plate:
When reassembling the clutch, check for original paint marks on the 3 pieces of the clutch. According to BMW, the 3 pieces (housing, diaphragm spring and housing cover) have to be reassembled with the marking at 120 degrees from each others.
The clutch is balanced at the factory and if you are not careful later you may experience vibrations.
When I remove a clutch I always put my own marking before removing any parts. The original one are sometimes really difficult to see.

Bert

Good idea to make the guide bolts to support and slide the gearbox back onto the bell housing.
Was there a specific reason that you cut them to length of 90mm (3.5") at all ?

I got some that are approx 140mm long is why I ask

the mule wrote:Bert

Good idea to make the guide bolts to support and slide the gearbox back onto the bell housing.
Was there a specific reason that you cut them to length of 90mm (3.5") at all ?

I got some that are approx 140mm long is why I ask

The reason why I had to cut them is because the gear box was touching the frame and not lining up with the engine.
I started with long bolts too, but quickly realized that I had to shorten them.

Bert

Thanks for the tip Bert will cut them tomorrow while waiting for gearbox to arrive. Where are you measuring the length from also

the mule wrote:Thanks for the tip Bert will cut them tomorrow while waiting for gearbox to arrive. Where are you measuring the length from also

If I recall correctly, this is the full length of the screw (including the thread).

Ok Thanks

Have just received gearbox from beemerboneyard seeing output shaft and 5th gear needed replacing and also seal and bearing seats in gearbox housing were badly damaged. Anyway just wondering how much freeplay or slack should be felt from the input shaft to the output shaft normally on the gearbox.

Cut the rods to length and got clutch all reground for new friction plate. went on like a breeze very easy found I had to engage 5th gear so I could rotate the input shaft to line up on clutch spline but went on no probs now waiting for replacement final drive to arrive to finish off reassembly

Hi Bert, seems that I'm coat tailing on this one. I have the gearbox off and have had to rebuild its bits and pieces. See my other postings in the general topic section and gearbox section. Thanks for some sound advice, and if you have any ideas about the clutch push rod not seating fully home, advice would be most welcome. Cheers Boris the Bike.

have you followed the procedure for setting the clutch cable back up.
back off the handlebar adjuster until the measurement at the gearbox end of the cable is 75mm +1 between the end of the sheath and boss at end of cable.
Then adjust the screw on the pushrod lever until there is light pressure at the back of the clutch rod piston.
Then you have to reset the handlebar adjustment so that there is a small amount of freeplay on lever measured gap of 5mm
finally reset the side stand mechanism so when the stand is down it pushes the lever back and removes the freeplay out of the lever.

Cheers Mule. Yep, that is the advice that the local BMW dealership gave. It came out of hand written school exercise book that the very helpful chief mechanic brought out from the back with comments like "aint seem on of them for a whole". Amazing, the lined exercise book was a posh dealerships 'workshop manual'. Says something, not sure what though. Trouble is the thrust piston stands proud of the gearbox housing by 5mm+ and it should sit in its housing. This is caused the Push rod (clutch) will not fit properly to its full length. I'll sort it one way or another.
Taking off the gearbox ect. has also revealed both swinging arm bearings as slack as a witches nickers. Utterly knacked. I thought I had got a sweetie when I bought this K100rs last autumn. Seems that it was a little tired!! Ah well, work progressess, although the Easter run looks out of the window. Cheers Boris the Bike.

Hi Boris,
I know just what you mean I was born in London and lived in the UK for nearly 40 years and most garages are crap. I recall the Consumers Association saying in their magazine Which (a mag for subscribers that tests various products and services) "If you have your vehicle regularly serviced by a dealer you are probably severely neglecting it" Says it all really and Boris' experience with the exercise book shows what the better one's are like they at least have exercise books! The others work on the basis of throw parts at the bike, at the customers expense, till it is fixed and no way do they refit the old parts when the new one did not fix the problem.

I recall a friend who had a brand new BMC 1100 that had a warranty failure (hydraulic fluid leak) of the brake master cylinder and took it in to the dealer to get it fixed, when he collected it he got 1/2 a mile down the road and smashed into the back of a row of cars at the lights because it turned out the mechanic had forgotten to fit the retaining split pin in the end of the clevis pin that attached the master cylinder to the brake pedal and it had dropped out leaving him with no brakes other than the handbrake, which if you know the 1100 was CRAP. Garage initially refused all liability but buckled at the end of a protracted wrangle.
Regards,
K-BIKE

Hi K Bike,
The BMW dealership Vines has been very helpful. You are right about the attitude towards fixing and the parts used though. Their advice was they just replace the whole clutch as standard. Yep, they keep throwing bits at the bike till its fixed regardless of the cost. We aint all "BMW" types owners (read 'posh car' here) with deep pockets. Still, I was sort of impressed with the exercise book 'workshop manual'. It was written out with huge care and must have had a great deal of experience contained in the pages. The chief mechanic even asked if I wanted a photocopy of the relevent page. Thanks for the help offered by all of ya, and I'll keep you updated with work in progress. Ride safe. Cheers Boris the Bike

I used some spare exhaust manifold studs as dowels to align the gearbox,they are just big enough, same thread and worked a treat.