All those years working on 1150 bikes, some of them having the gearbox input shaft in perfect shape, some having it worn out… Weird, right? Cars and trucks have a different way of connecting the engine to the gearbox, the clutch is somehow floating, there is an intermediate shaft and miss-alignment issues just do not exist.

Why not all of them? Why just some of them?! Why does this not happen for the 1100 boxers or the 1200 series?

I have recently worked on a 2001 R1150GS, which had a weird sound while the engine was idling. It was not the usual noise these bikes make that goes away when the clutch is pulled in, no, this was much worse.

When taking the bike apart, there was lots of oil on the gearbox side of things, and this…

Upon a closer look on the cleaned shaft, you can see that the wear is not along the splines, more towards the middle of them.

For me, that means that the whole clutch pack assembly moves in a figure 8 shape, instead of going PERFECTLY ROUND O

So… since I have a lathe, I decided to check it for trueness. A round piece was fitted into the universal and trued on the front side, then the flywheel press fitted over it.

Since ever, I thought that the gearbox and the engine were not perfectly aligned, because of the dowel pins, and that results in the wear we all know, specific to the/some 1150 bikes.

However.

I know BMW started using CAD/CAM with the 7 series car back in 89′. These bikes were definitely built using CAD and CAM, and milling the dowel pin slots in the engine and the gearbox housings would be a piece of cake, just do one side and mirror your code to the other side. If something was not right, the distances incorrect, the gearbox would never mesh the engine, but they all do, perfectly.

My guess, at this point in time, is that the flywheel, being it press formed, was not perfect on the faces where it meets the clutch pack. A step has been bypassed when producing them, they should have rectified them to make sure that the engine contact spot was parallel to the outer of the flywheel.

Long video short, check out how it sounds when faced in the lathe, instead of the 3 equally distant sounds, you can only hear 2, meaning one third of the flywheel is not on the same plane with the other two, meaning that the clutch pack is not spinning perfectly round, meaning it would eat out the input shaft.

After facing the flywheel, I have fitted a new friction plate, the old one was soaked in oil. The other parts were washed and cleaned and fitted back. The clutch had 6mm thickness, 70% life still left in it, should it not be soaked with oil.

The gearbox was opened, the bearing replaced and the whole bike put together back.

Now, a complete test would be, IMHO, like so:

-open the bike again in 50k kms and check the wear on the shaft again

-(not likely to do) for a bike that has a high mileage and a perfect, un-worn shaft, also test the flywheel on the lathe.

I think I will go with option 1, perhaps many winters from now. I measured about 1/10 mm, so not too much material was removed. But it was all it took for the shaft to wear.