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Main seal?

The place to discuss the R 90 S as well as the R90S Worldnet archives!
BigWally
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Re: Main seal?

Post by BigWally »

I have 5 bikes (2 airheads) so I keep detailed records including parts sources & costs so I don't get details mixed up. On 2 occasions I've needed to notify a vendor of a real or perceived problem with their parts supplier.
The perceived problem was an "out-of-spec" oil pump outer rotor OD. They checked their inventory and all of them had the same OD. Upon further research I found a UK parts dealer that reported that BMW changed their spec on that part and all of them at my supplier were within the new spec. My supplier appreciated the updated info.
I note that I've never seen the actual BMW bulletin advising of this spec change but have assumed its out there somewhere.
'73 R75/5; ‘84 R100S Last Edition (California version); ‘84 R100RS; ‘08 R1200RT

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San Arthur
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Here we go again!

Post by San Arthur »

In order to check the rear main seal one must remove the gearbox, but things got out of control and...

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San Arthur in San Antonio, Texas
'58 R26 '76 R90S '88 R100RS '94 R100GS/PD

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San Arthur
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Frame failure

Post by San Arthur »

Main Seal Replacement

While tackling the removal of the swingarm to access the gearbox and investigate the source of an oil leak, I came across a familiar issue often discussed on this forum—a typical frame failure that seems to plague many /6 models.

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Initially, I considered addressing the metal fatigue crack right on the bike. However, I decided to take the more thorough approach: stripping the frame completely of all components. I’ll be taking the bare frame to Gary, who will weld the crack at his place, and then give it a fresh coat of paint.
San Arthur in San Antonio, Texas
'58 R26 '76 R90S '88 R100RS '94 R100GS/PD

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San Arthur
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Final Drive Thread Issue

Post by San Arthur »

Final Drive Thread Issue

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While draining and refilling the gear lube in the final drive, I discovered that the threads in the final drive case itself are stripped—not the bolts, which are in perfect condition. Here’s a picture for reference:

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Since these bolts are only used for draining and filling gear lube, I wonder if this is something I can leave as-is, considering they don’t seem to require much torque. However, could there be any hydraulic pressure inside the small compartment that might stress these threads further?

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My question is: should I rethread the holes to 14mm, or would it be safe to leave them as they are? Any advice or experience would be greatly appreciated!
San Arthur in San Antonio, Texas
'58 R26 '76 R90S '88 R100RS '94 R100GS/PD

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srankin
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Re: Main seal?

Post by srankin »

I myself would rethread. St.
Owner of a 84, R80RT and 79 R100RT being stripped naked for summer, turned Into a frame up restoration,

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San Arthur
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Re: Main seal?

Post by San Arthur »

srankin wrote:
Tue Dec 03, 2024 10:28 am
I myself would rethread. St.
Thanks for writing, machine shop or by hand? I’ve only refresh threads but never re thread to a bigger size.
San Arthur in San Antonio, Texas
'58 R26 '76 R90S '88 R100RS '94 R100GS/PD

flyingtpot
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Re: Main seal?

Post by flyingtpot »

From the pics, the majority of the threads are gone/toast, so 'cleaning up' or rethreading the current M12 threads with a tap is not feasible.

I do that repair by installing Time-Serts. It makes for a robust quality repair. Heli-coils are weak for the application and the depth is not ideal for using them. Tig welding and tapping is another repair process. Yet it is cumbersome, time-consuming and not forgiving to any impurities that were not removed from the casting.
Last edited by flyingtpot on Sun Dec 08, 2024 1:26 am, edited 1 time in total.

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srankin
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Re: Main seal?

Post by srankin »

You have sharp eyes.

I should have looked a little bit more at the pictures. Sorry, St.
Owner of a 84, R80RT and 79 R100RT being stripped naked for summer, turned Into a frame up restoration,

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San Arthur
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Time[Serts

Post by San Arthur »

flyingtpot wrote:
Sat Dec 07, 2024 1:28 am
From the pics, the majority of the threads are gone/toast, so 'cleaning up' or rethreading the current M10 threads with a tap is not feasible.

I do that repair by installing Time-Serts. It makes for a robust quality repair. Heli-coils are weak for the application and the depth is not ideal for using them. Tig welding and tapping is another repair process. Yet it is cumbersome, time-consuming and not forgiving to any impurities that were not removed from the casting.
If I’m going to cut new threads to install the Time-Serts, why not just rethread the hole to a larger bolt size instead? Since the bolt is primarily for refilling and draining oil, and high torque doesn’t seem critical, wouldn’t this approach simplify the repair? Curious to hear your thoughts on why Time-Serts might be the better choice here.
San Arthur in San Antonio, Texas
'58 R26 '76 R90S '88 R100RS '94 R100GS/PD

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San Arthur
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Clutch

Post by San Arthur »

I recently removed the clutch from my 1976 R90S, which was replaced by a BMW expert no more than 5,000 miles ago. Upon inspection, several issues were evident:

Clutch Disk:

The clutch disk appears to have glazing on the end corner, potentially caused by oil seeping up from the engine.
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I believe the recommended thickness for replacement is less than 6 mm, and my measurements confirm that it’s borderline:
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Pressure Plate:

The pressure plate also looks worn out, with noticeable scuff marks and signs of fatigue:
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Additionally, there is glazing and blue discoloration on the opposite side, likely from overheating:
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Compression Ring:

The compression ring appears to be nearing the end of its service life, showing visible wear and fatigue:
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Diaphragm Spring:

The diaphragm spring has scorch marks and will need to be replaced as well:
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Next Steps:

Based on the wear and damage across these components, it seems the entire clutch assembly—including the disk, pressure plate, compression ring, and diaphragm spring—will need replacing. I’d appreciate any advice or recommendations on parts and ensuring the engine isn’t leaking oil into the clutch housing again.

What do you think caused the uneven wear of the clutch disk?

Thank you for any insights!
San Arthur in San Antonio, Texas
'58 R26 '76 R90S '88 R100RS '94 R100GS/PD

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