I have a better output shaft that I'd like to put into the '85 K100RS, just a 6 rivet swap, but I feel the new one is better. Anyhow, I'd like to do this with the engine in the frame if possible. What steps should I take? I'll have to pull the FD and trans obviously, but can I then work under the engine to remove the output shaft, or am I doomed to pull the motor?

bell housing might be the restriction but maybe possible

First buy enough beer, then check this document.

Inge, nice find on the output shaft document .

sounds like a slab job (24 stubbies in a slab ) giggle

24 of these ones would be the correct amount:

now thats output!

.....thanks inge ....read my mind ...giggle

Well I have a good 1/3 of the bike disassembled and have had a thought... how will I support the engine in the frame if I remove the gearbox and intermediate housing? Normally I would support from underneath, but in this case I need to remove the sump to access the output shaft. Any clever ideas before I abandon plan A and remove the engine?

A piece of plywood, using some of the intermediate flange mounting points.
Some length of ~2"x2" (or whatever) across the frametubes.

Lay the bike on its side?

Yes, you'll need to make a support bracket to pick up some of the holes at the rear of the engine, above the split line. You may also consider removing and examining/cleaning the starter sprag clutch while you are in this far. It may well be OK, but it would pay to check it out. Make sure you replace the O ring at the crankshaft nut, the nut is also supposed to be replaced, and there is a special tensioning procedure (in the manual).

Dennis wrote:Make sure you replace the O ring at the crankshaft nut, the nut is also supposed to be replaced, and there is a special tensioning procedure (in the manual).

I may add that also the compression ring between the O-ring and nut is supposed to be replaced.

If you remove the air filter base there be a couple of bolt holes you can run a strap up to the frame rail from. The hardware store should have a metal strap for you

Well that was a much more time consuming job than I first thought. Thursday evening, all day Friday and finished up Saturday morning. And a major difference in cold start up, now it is quiet! I didn't realize how noisy it was until the output shaft was swapped out. As was mentioned elsewehere, it is a very deep part to change out, but I was able to do it without removing the motor. Thanks to Inge for that service bulletin. The engine support ideas were all excellent, I went with a hybrid approach as shown below. My saddest moment was removing the oil pump that had given me so much leakage grief. I haven't taken it out on a good ride yet, but up and down the street it seems to be sealed. Thanks to all who contributed.

onya clubbie !!!

wanna come and help me do mine ? giggles

im guessing ill be off the road for weeks

Noted your picture; do you have one from the left side of the bike? Or do you know how far the outlet pipes stick into the muffler? Strange question maybe, but I can't get the muffler off and wonder if my repair of a cover plate attachment with a well nut is the problem............

the pipes go in to the muffler about 2 inches

Club_c,
Did you notice how there is much less play in the drive train?

good point yankee .....clubbie is there any difference in the free play of the back wheel whilst in gear ?

(it was pretty common to see about 50 mm from a survey )