Replacing crown gears on final drive - r90 project
 

I spent $500 on new parts for the final drive on the r90 project bike. Getting ready to dive into in a few minutes with a buddy of mine and the manualk.

Any words of advice? I can see from reading through the manual it's a painstaking job.

Leftie loosie, righty tighty!:D

geez, thanks guys.

Shannon,

First off, what are you planning on doing?

The final drive requires special tools to dismantle. And they really are needed, no two ways about it. It is possible to replace a few seals and gaskets without them, but that's about it.

If you're planning on replacing the ring gear you're in for a job. I've never done that, but a friend of mine here who's been a mechanic all his life and his first bike was a bmw - and he's been a bmw mechanic for a long time, running his own shop, in fact - told me about a time he installed new gears in a final drive. As I recall, he worked a whole day on getting it adjusted correctly, and it wasn't any fun. I got the idea he's never done it again, and doesn't intend to either.

I rebuilt a rear end on a chevy van I had and it took quite a while. Even then, I was never sure I got it adjusted exactly right. It ran fine after that, but the truth is in whether it held up. If the gears aren't adjust just right they'll wear quickly. I probably did just fine, but not having done it before I was never sure I did it well enough.

I have taken the ring gear from a final drive, sent it out for spline repair, and replaced it. That went just fine. But in that case I was just replacing it with the same that came out of it so the adjustments and gear alignment weren't disturbed.

There are only two things I'm having trouble with disassembling.... I'll take them up to the dealership tomorrow and see if they can get them pulled off. I don't have the book in front of me and I forget what they are called. One piece is off the ring and the other, the pinion.

As far as spacing the gears, the book I have is pretty detailed and it will take some time, but I am confident I can get it right eventually following directions.

Any gotchas would be good stuff though.

There is a possibility the mechanic I told you about was attempting to scare me away from ever doing that job. I'm curious how you'll make out.

By the way, you never told us what you're doing to the final drive. Are you replacing the ring gear because of worn splines?

what's a spline?

Just kidding.... the ring gear was worn more than I was comfortable with. This bike will be new when I'm done with it.

Here's the whole story if you're unfamiliar....

http://www.bmwforums.net/forums/viewtopic.php?t=101

Roger????

Cough.

Roger.... this thread is not going away... tell me something, please.

I'm sorry for posting the old pic of you. I thought you would think it was funny.

If the splines are worn, it's much easier and cheaper to have them rebuilt. Hansen's in Medford Oregon did mine and they came back beautiful. You couldn't tell them from new.

If the gear itself was worn, then I understand. But I've never heard of that happening.

crown gear.... now you've heard of it. I wouldn't even consider spending this much time and effort if I and others didn't think it should be done.

I did think it was funny, Just really really busy.
I just about never see those wear. The bearings maybe (but rarely) unless run dry. Of course, new bearings mean an all new measuring and shimming job. The work sucks, with a fair amount of trial and error unless you do it all the time. I certainly don't fall into that category. I normally just replace seals and then reassemble. Be careful on the pinion nuts, seal, and packing, or she'll leak on you. It requires a fair number of special tools to do right. It's the only thing outside the motor bottom end that I think you shouldn't try yourself.

Return the hard parts if possible for money and follow Rogers advice.

I do all my own work, including tranny rebuilds, but left the bottom end rebuild for my mechanic friend. I thought I might be able to tackle that myself, but once I had it described what's needed, decided against it. It's one of those things that requires a certain familiarity - with practice you could probably do a very good job. But don't expect much the first time around. I figured it was worth it to have an experienced hand take over.

This same friend was the one who had me send the ring gear to Hansen's for spline repair. Turned out great (and is supposedly much stronger than new) and only cost a couple hundred bucks all together.

bearings are good

the round gear is worn, which means I have to replace the rest of the gears. I'm replacing the gasket, but the seals all look good.

The hardest part it looks like is spacing the gears correctly. Do I get some sort of award if I pull this off?

Also, my "team" collectively came to the conclusion we should and could do this. One guy is an x racer, so I'm confident. I think.

Fly me to Phoenix, and I'll do it for you.

Sounds doable for you guys Shannon. Half of the game is not being easily intimidated and being patient and perseverant, so it IS doable, just not fun or easy. The gear spacing "mesh" is the tricky part. Have you ordered a selection of shims for the main bearing?

In any event, it is to me inconceivable to go to all that work and not replace those seals. It is rare for anything to go wrong back there that isn't a seal. At the very very least, the pinion seal and packing should be replaced, as it's buried behind the gear/washer/nut etc. When that seal goes, then the driveshaft fluid can run down into the rear drive.
You end up with a messy/spewing rear drive, and a dry/non-lubed driveshaft, neither of which is particularly desireable.

Good luck!
Roger