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Old 07-12-2012, 01:07 PM   #1
Mista Vern OP
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Question A weird final drive situation

I am refurbishing a 79 R100RS and was in the process of changing the final drive from a low ratio sidecar one to a more normal one. All was going well until I found the rear wheel wouldn't turn. Huh?

Took everything off and checked the final drive and it is just fine, but learned that in some odd cases the castings/nubs inside the hub part of snowflake wheels interfere with the final drive. My friend, Wirespokes, says this occurs once in a while and is due to either an earlier wheel and a later final drive or vice versa.

Anyhow, anyone else run into this and if so, is there an easy way to figure out how much metal to take off the wheel hub nubs so everything spins as normal, or do I just keep messing with interference marks until things are good?

Sorry if this isn't clear - kind of an odd problem that doesn't lend itself to proper nouns.
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Old 07-12-2012, 01:18 PM   #2
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Just had a bit of a thought ...

After reading this I think I understand your problem. You are rubbing somewhere in the shaft or bell housing of the swingarm ... right? Does it turn at all?

If it's the shaft, it will be rubbing on the center of the swingarm ... this can be 'fixed' by shifting the swingarm to the left (as you are sitting on the bike). Moving it just a micron should tell you if that is your problem.

Secondly, if it's the bell housing that is rubbing the final drive housing then, you will probably have to remove the shaft and taka little meat off the housing. And you can diagnose this one by getting a Sharpie (marker) and putting several lines down the bell housing ... and then doing an install, and trying to turn. if it turns at all, you should be able to see if the bell housing is scratched (marker removed) ...

Thoughts? Am I way off?
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Old 07-12-2012, 01:21 PM   #3
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Right side wheel spacer that the seal rides on still there?
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Old 07-12-2012, 01:24 PM   #4
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Quote:
Originally Posted by Beater View Post
Secondly, if it's the bell housing that is rubbing the final drive housing then, you will probably have to remove the shaft and taka little meat off the housing. And you can diagnose this one by getting a Sharpie (marker) and putting several lines down the bell housing ... and then doing an install, and trying to turn. if it turns at all, you should be able to see if the bell housing is scratched (marker removed) ...

Thoughts? Am I way off?
It's this, and yep, figured on doing that - was just hoping that some could say, "Yeah, cut 3/8 inch off at a 40 degree angle" or something like that.
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Old 07-12-2012, 01:25 PM   #5
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Quote:
Originally Posted by robtg View Post
Right side wheel spacer that the seal rides on still there?
I'll double check, but am betting so. Thanks!

Edit: due to the interference, it's not even getting that far in, but I will check.
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Old 07-12-2012, 01:34 PM   #6
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Quote:
Originally Posted by Mista Vern View Post
It's this, and yep, figured on doing that - was just hoping that some could say, "Yeah, cut 3/8 inch off at a 40 degree angle" or something like that.
I know this would be tough ... but post some pics. (You can also email them to me, and I'll post).

The bell housing isn't even slipping into the final drive? Can you tell how much clearing there needs to be? Can you send me an accurate diameter measurement of your bell housing?

Does anyone know if the '79 bell housing was a little beefier than usual?

You have a standard length swingarm, right?
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Old 07-12-2012, 02:56 PM   #7
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Quote:
Originally Posted by Beater View Post
I know this would be tough ... but post some pics. (You can also email them to me, and I'll post).

The bell housing isn't even slipping into the final drive? Can you tell how much clearing there needs to be? Can you send me an accurate diameter measurement of your bell housing?

Does anyone know if the '79 bell housing was a little beefier than usual?

You have a standard length swingarm, right?
The splines mesh so that is fine - they just don't go all the way to where they are supposed to be. The chances of me being able to take pics are slim - I'll just putter away until it all fits. Thanks for your suggestions!
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Old 07-12-2012, 03:05 PM   #8
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Take 3/8 ths of an inch off at a 40 degree angle....................problem solved.You knew it all along.
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Old 07-12-2012, 03:21 PM   #9
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Take 3/8 ths of an inch off at a 40 degree angle....................problem solved.You knew it all along.
Thanks!
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Old 07-12-2012, 06:22 PM   #10
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The service bulletin said, regarding using a finned final drive with an early wheel:
"Rear wheels with disk brakes manufactured before 1981 have 12 lugs located in the hub. Before mounting the wheel, it is necessary to machine the lugs off."
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Old 07-12-2012, 08:23 PM   #11
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Anton has it. I've done it. It works fine.

You can just use an angle grinder to knock them off carefully. Here is the service bulletin that described doing that.

https://www.bmwmc.net/catalog/33%200...%282253%29.pdf

https://www.bmwmc.net/bulletinsearch.asp

I once had photos of me doing this, but I can't locate them now. Sorry.




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boxerboy81 screwed with this post 07-12-2012 at 08:53 PM
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Old 07-12-2012, 08:27 PM   #12
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Thanks Anton and boxerboy. Now I pretty much know I am not totally clueless. Since no specs were given I am going to guess that this is a by just getting in there and doing it using a chalk or a grease pencil to see where things are hitting.
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Old 07-12-2012, 08:55 PM   #13
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Quote:
Originally Posted by Mista Vern View Post
Thanks Anton and boxerboy. Now I pretty much know I am not totally clueless. Since no specs were given I am going to guess that this is a by just getting in there and doing it using a chalk or a grease pencil to see where things are hitting.
I just ground them off so that the whole inner surface was smooth, like a newer wheel. I had that wheel off the bike a few days back...I could've taken a picture then if I'd known.
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Old 07-13-2012, 08:33 AM   #14
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Thanks again, boxerboy.
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Old 07-13-2012, 08:04 PM   #15
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I had that problem with my '79 RT a couple of years ago. I was thinking of grinding/turning the lugs off but didn't do it and put my old FD back again.


1979 FD


1981 FD


1979 wheel
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