R90/6 No Cylinder Gasket or O-ring??

[marcn113]

R90/6 No Cylinder Gasket or O-ring??
My 1975 R90/6 I just got it and has a oil leak on the right side cylinder. When I took it apart I found no gasket, no o-rings. There is a groove but it seems to big and high to be for an o-ring. How can I be certain what should be there or is it possible no gasket goes there; maybe just some sealant??

 

[rocketman]

Cylmer shows a gasket that fits around the four studs, a small "O" ring around the two upper studs (that's where the oil feed is to the head) and a large "O" ring around the base of the cylinder on some models, so if there is a grove in the base of the head I would bet your model came with the large "O" ring.
Ask your dealer they would have a parts diagram for your year/model.

RM

and as a side note, I'd suggest you only keep this one thread going and remove the one under "how do I" since it will be easier to track responses and this is the more appropriate forum area for this type of question.
Thanks and good luck rebuilding the bike.

 

[johnpeter]

Someone may have taken the gasket out trying to increase compression about .5.

A gasket is shown here. Do save this site. http://www.maxbmwmotorcycles.com/fiche/MainDiagrams.asp?mospid=47839

Note: Removing the gasket would tighten up the squish band. Squish is safe for most street bikes at no less than .7 mm.http://www.muller.net/mullermachine/docs/squish1.html

 

[Rod Sheridan]

My 76 R90/6 has a very thin metal base gasket and the two O rings around the top studs.

The cylinder bases have no grooves for an O ring on mine.......Rod.

 

[1978r100s]

I have just gone through the same on my 78 R100s. I wrote Oak about this and below in part is what he had to say. Actually had a post here on "cylinder gasket" which gave me lots of help.



"The 78 models were a mixed bag in production. Some had the large O ring around the cylinder base, others did not. If you do not have the groove for it in the cylinder base, do NOT use the large O ring. There is no room for it.

There is NO base shim or gasket on ANY of the engines produced beginning 1976 unless someone added them. Some did, to reduce compression ratio as a means of dealing with lower octane fuels. The best fix of course for that is retaining the stock compression ratio of 9.5 to 1 and going dual plugging"

ej

 

[marcn113]

Here is a picture of the cylinder. I don't think this grove is intended for an o-ring. I am thinking I should attempt this without the o-ring. My trying to be prepared for whatever, I have the metal gasket, large and small o-rings standing by. I suppose if I'm wrong I can always go back and add the o-rings. Anyone can tell by looking at this picture?

Thanks

marc