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Old 11-20-2014, 01:23 PM   #1
woodly1069 OP
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Different versions of cylinders?

Totally confused here and wondering if anyone may help me sort this out. My 1978 R80 has been leaking oil from pushrod tube seals so I pulled the cylinders to replace them. Problem is there was no base gasket? There are two small o rings around the upper studs but no base gasket and no large oring to seal the spigot. There does seem to be a small step in the cylinder where it meets the engine but no place for a big o-ring. Is there any way this could be correct? I did see some evidence that there was some sort of RTV or sealant around the base of the cylinders where they meet the block. Was this done at the factory? The following is a picture from BMW...as usual, any information would be greatly appreciated.

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Old 11-20-2014, 02:32 PM   #2
supershaft
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Yes, that can be correct. My '83 came with no sealant. With cylinder O-rings. If your bike isn't machined for the cylinder O-rings, you can't use them. BMW sells two different size cylinder O-rings. A lot of people are not aware of that. They seal best with the cylinder O-rings and sealant. Use what you can. I use Durko brand sealant with real good luck (on a professional basis) carefully spread as thin as possible with a square Exacto blade. New BMW pushrod tube seals Scotchbrited clean inside and out and installed clean and dry. Dry cylinders (no oil for the rings). Retorque and readjust valves after a couple of heat cycles, not 600 miles. Do the same at 600 miles again. Be careful and double check right before the cylinder/case gap closes that both stud O-rings have not fallen down and are resting on the studs. If so you need to get them back in place. Otherwise they distort the cylinders/case and cause oil leaks that are very difficult to fix for the permanently F'ed up cylinders/case.

supershaft screwed with this post 11-20-2014 at 02:45 PM
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Old 11-20-2014, 02:35 PM   #3
woodly1069 OP
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Hey Shaft do you mean the o-rings for the studs or the OD of the bore? I would assume the large o-ring would have some sort of channel it sits in?
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Old 11-20-2014, 02:39 PM   #4
supershaft
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Quote:
Originally Posted by woodly1069 View Post
Hey Shaft do you mean the o-rings for the studs or the OD of the bore? I would assume the large o-ring would have some sort of channel it sits in?
The cylinder O-rings are the cylinder O-rings and the stud O-rings are the stud O-rings. I was talking about both depending.
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Old 11-20-2014, 02:40 PM   #5
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right on man, thanks for the tips!
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Old 11-20-2014, 04:13 PM   #6
190e
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Didn't at one point BMW change the size of the cylinder base O rings from 2.0mm to 2.2mm in section.
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