to BASE GASKET or not to BASE GASKET

[grant81rs]

Gidday

I quick teaser to end the year on fellas..

I have a leaking push rod tube seal on the right side, this I knew about from the PO when I brought the bike as it was about the only thing he said needed doing before this bike could be ridden around Australia as it was hhhhmmmmm ya sure about that one!!

So I have watched the 3 x part Youtube videos on push rod tube seal replacements from Chris Harris at affordable beemer services who is now called Team Monkey Productions btw, the vids I have studied a few times to get me in the groove to do the repair when the parts arrive.

My bike is a 1978 R100RS and my question is regards to a base gasket at the crankcase /cylinder head and do I or don't I use/replace them as the RealOEM site does not list any for that year but does list a gasket sealant only?

Also on the Chris Harris vids I did not see any base gasket come off or go on, only a new O-ring being replace and new head gasket and nothing was mentioned about base gasket that I remember, but on the Motorworks new parts site it does list base gaskets for all r100's.

I was a little confused, so I just brought all the new parts for the job, plus the gasket sealant but minus the new base gaskets

Can someone advice if I am wrong or explain the pro and cons of no base gasket etc or yes they are recommended!!

Thanks for any info received

[Kurt in S.A.]

I'm now a little confused with what a "head base" basket is. I thought there was a head gasket and a base gasket. At any rate, I just did a Sept. 1977 R100/7 top end and there was not a cylinder base gasket or large o-ring...I just used a light smear of Permatex Ultra Gray. There were of course the small o-rings on the top studs...there's actually an relief cut on the cylinder base to accept them.

Kurt in S.A.

[2valve]

Max BMW site shows for your year model , the O ring for the base of the cylinders and also shows a tube of sealing compound to use. Im not sure of this but the early BM's before/up to 1976 had the old base gasket style if needed , then they started to use the O ring style for the base of the cylinders for your year model .I usually go to Max BMW web site to look for parts etc may help you. The parts that you have ordered are a set of O rings for the base of the cylinders and a head gasket /push rod seals ?

[Duane Ausherman]

BMW changed that system a few times in an attempt to stop the ooze of oil. One can interchange them without trouble if only one thing is remembered. Cylinder wear at the top could cause the top ring to hit the ridge worn by wear. Or, if one ran it with the thicker base gasket, or three of them, then removing the base gasket would certainly cause interference. That could even cause the top ring land to break off, or wear very quickly. It would probably make a noise too.

[chasbmw]

Whether you have a base gasket or an O ring bike always use sealant.

[barryh]

A 78 should have the groove for the large O ring at the cylinder base. If the groove is there it needs an O ring but no base gasket. If the groove isn't there then it needs a gasket.

BMW originally intended that no sealant be used after the large O ring was introduced but they changed the dimensions a few years after it's introduction. The Original O ring was a 2.2mm section and that was changed to a 2.0mm section O ring. A properly engineered O ring seal shouldn't leak. 2.2mm may have been too big but maybe 2.0mm is too small hence the almost universal recommendation to also use sealant in addition to the O ring.

[Duane Ausherman]

Bike sales were off in 76, 77 and 78, so many got sold as later models because the dealer would lie about it and the dealer also fills out the paper work. This happened from time to time anyway, but during that period it increased a whole lot.

What I am saying is that don't allow any confusion about what is right for your year, or what you think is your year. If it has a groove, use an "O" ring. If you found no base gasket, don't use one. If you found 1,2, or 3 base gaskets, use them again. I would use sealant in all cases.

Just be sure to not squish the dough nut too much, or the rubber can crack and leak way too early.

If I knew the bike and history well, I might be tempted to just cheat by sliding the cylinder back a bit and slipping in the new dough nut. I prefer to pull it down completely and check the rings and valve guides too. In a shop it is too easy to get bitten by such a short cut. As a private owner you aren't likely to sue yourself for faulty work.

I remember a couple of times that we had a poor customer who needed that job done. We really liked them so we would actually pull it down properly and charge for the short cut. It really isn't much more of a job to do it correctly the first time.

Be sure to carefully examine the pushrod for wear where it goes through the head gasket.

[Kurt in S.A.]

My early '78 has no groove/no gasket; so it got no large o-ring or gasket but I did use sealant.

Kurt in S.A.

[grant81rs]

My early '78 has no groove/no gasket; so it got no large o-ring or gasket but I did use sealant.

Kurt in S.A.

Many thanks for all the feedback and interest and yes, what I found when I removed the cylinders was just the same, there was no o-ring and no gasket used and the bikes VIN is listed as a 6th month 1978.

I used a sealant which was listed and recommended by http://www.motorworks.co.uk and was guided by a few on here off-line about the importance of not to over use... No leaks or weeping so far!!

[ME 109]

As a private owner you aren't likely to sue yourself for faulty work.

I did. I had to.
Cost me a fortune in parts to fix my major stuff up. I settled with mesself out of earshot of the wife.