I'm doing a rear main seal/o-ring replacement along with a spline lube and replacing pretty much every bit of rubber from the engine to the final drive right now. I had just finished putting the transmission back on when I noticed a washer on the ground that I don't recall taking out. My camera's broken right now so I unfortunately don't have any pictures, but it's 40mm outside diameter, around 33mm inside diameter, and 1.5mm thick. It looks like it's made of copper.

At first I thought it might have been the thrust washer - #10 in the lower left in this pic:

 

but it seems too thick for that - those are 1mm or 1.25mm. Also my K100 was built in late 1984 and I've read that thrust washer isn't present on some of the earlier Ks.

Any ideas? Thanks everyone! This forum has been a huge help as I work my way through this whole procedure.

http://realoem.com/bmw/showparts.do?model=0501&mospid=51746&btnr=11_4681&hg=11&fg=21Is
it part 19 on this link?

Does that sit behind the ball bearing (#11)? I never removed that.

It most likely came out when you removed the clutch carrier they usually do.

Dang. Well, I guess I'll be ordering a couple more o-rings so I can get back in and put it where it should be. Hopefully I can piggyback it on the order for the clutch boot that I didn't expect to break, haha. At least I know what I'm doing this time!

Thanks!

They aren't exactly easy things to get out those O rings. I have had success with a .6mm piece of MIG wire with a small 90° at one end to get behind then work it out with the thread going round and round but I think that at $1 each they aren't worth the trouble.

Okay, I took the transmission, clutch pack, and clutch housing, destroyed my o-ring, and got back to the rear main seal/output shaft area. But the washer doesn't fit! With it in place, there is no way to get the clutch housing back on the output shaft. So, it can't be the thrust washer or the shim from either of the diagrams here. I inspected the starter while I was taking the trans out, could it be part of that?

Got my camera working:



Still a mystery!

looks like a sealing crush washer to me.
I'm not at all sure......does it happen to match the drain plug or fill plug for the trans????
Ibjman

what about an exhaust pipe gasket to the cylinder head?
 Did you have any of the header pipes off?

YES!!! It is the exhaust header to cylinder seal! I just went out and checked and 3/4 of them are there! Thank you so so so much ibjman, I can sleep tonight!!!

11 62 7 662 083  GASKET RING - C32X40    4   $2.19......Part #4 in the picture



Regards, Ibjman

Sorry you had to go all that way back in for nothing........sometimes mechanical lessons are hard learned

If I didn't have at least one story about putting something almost completely back together before taking it back apart for no good reason, I wouldn't be much of a mechanic.

I was just in your city 10 days ago with my wife & met up with 3 others from the forum at the Salem BMW rally.
Any chance you made it there?

Unfortunately I missed it, I had made plans for that weekend far in advance that I couldn't change once I realized. A couple of friends of mine made it down there and made me real jealous when they told me all the different bikes they tried out. Next time, definitely!