Oil leak at cylinder base

[corvair]

I got my fully restored 1961 R69S about 3 years ago. I dont ride it much (300 mi/year?) Ever since it's been leaking oil at the base of the right-side cylinder. Makes a bit of a mess while riding as an oil mist is blown towards the rear. I originally thought it was coming from near the lower/forward cylinder "stud". I replaced the cylinder base gasket (and head gasket at the same time). It still leaked! Not being a mechanic I chalked the "first time" as a learning experience. So I did it a second time... still leaked but now it looks like it's coming from the pushrod tube seals into the block, which I did not replace the first time as they still seemed soft. OK, for the third time I replaced base and head gaskets AND pushrod tube seals... It still leaks today!!!
Very careful observation while bike is hot and after cleaning the area with brake cleaner spray... I am revving up the bike while on my back looking under the cylinder (I have a long arm!) First I noticed some tiny "bubbles" between the cylinder stud and the nut. All of a sudden a drop of oil comes out of who knows where and runs along the cylinder base onto the bottom of the block, about half way between the nut and the lowest point of the cylinder base flange. I am pretty sure it does not come out where the "oil drain tube", coming from the head, enters the cylinder flange. It certainly did not come from higher up the cylinder as everything is still squeaky clean up there. I can wipe the area clean and make it happen multiple times by revving up the engine, or rather when the engine slows down to idle after I revved it up.

Any ideas what I should try next?

[Twocams]

Some of those cylinder studs are drilled clear threw into the engine case. Oil can leak threw the threads. Get some good sealer on some good clean threads. Oil & heat resistant.

[corvair]

Thanks, Twocams!
If I understand correctly, not being a mechanic, I would have to remove the cylinder, unscrew the stud (with two nuts "locked" together), clean the threads, re-install the stud in the block with sealer on the threads, re-install the cylinder.
Something like that?

[Micha]

Twocams gave great advice.
I don't think its a must to totally remove the cylinder and unscrew the stud.
Try to see if you can pull the cylinder out but not to the end so that the piston with its rings will stay seated inside the cylinder (support them in some way).
Leave the stud inside its place. Also, you will take the pushrod tube seals out from their seat, of course.
Clean well with thinner or alcohol these rubber seals, where they sits (contact area) and also clean around the stud base and the opposite side that sits there - the cylinder base.
Be careful not to get the thinner into the engine.
After the solvent has dried, spread very little sealing material as Twocams suggested taking care not to block oil passages etc: Always apply very little of this material. A fine thin layer will be enough.
Put everything back together. Wait a day to dry and I hope this solves the problem.

[Daves79x]

Yes, the studs can wick oil from the crankcase and the threads should be sealed during the build. But more common is just a plain weep from the gasket here and there. The gasket should be lightly smeared with Permatex Ultra-Gray sealant - that will fix leaks there. But if it's coming apart again, pull the studs and apply thread sealant to those too.

Dave

[corvair]

Thanks for the advice Micha and Dave. I will try again a fourth time. Indeed, I used Permatex Ultra sealant on both sides of the base gasket the last time I pulled/re-installed the cylinder. Wish me luck!

[Twocams]

All good answers but if I took something apart for the 4th time I want to fix the problem. I just took the shut off valve off for the second time cause it was seeping on my 92 R100RT. And that got old fast....drain the gas.
So I would take the studs out 1,2,3,4, for sure the one that is leaking. The threads maybe pulled on the leaker (stripped). Someone may have got Ham Fisted and got the threads stripped on the Aluminum case? That's another problem so lets not go there. Use the "2 nut trick" get the stud out. Clean the threads on case/stud (s). Put your favorite goop on the threads & screw the stud back in. At this point you may want to replace the head gasket/ case gasket?

[corvair]

Follow up...

Gentlemen,
Thought I'd let you know what I found and what I did.
The two "forward" studs are in through holes that open into the crankcase. I easily unscrewed those two studs with two "jammed" nuts, applied Permatex thread sealant and put back them in. The two "rearward" studs do not "open" into the crankcase ("blind" holes") so I did not touch them.

I put everything back together, let everything "cure", the next day re-tighten the cylinder stud nuts, re-adjusted the valves, and started it up... still got oil leaking below the cylinder!!!

Finally, I think I found the source of the leak. I could not quite believe it so I asked a friend to confirm what I saw. There seems to be one, maybe two, pin holes in the cylinder flange, not far from the upper/forward stud hole. Out of one pin hole you definitely see oil coming out when revving up the engine. Out of the other pin hole there is a "shine" of the oil wanting to come out but not much, if anything, flows out of it. I did find pitting in the cylinder wall when I had it out but it was "outside/lower" than the compression chamber and rings travel so I did not worry too much about it. See photo.

I am going to search this forum for pin holes/porous cylinder casting issues. If I find nothing I will post another question.

Wish me luck!

[malmac]

That is an interesting condition.

It raises questions about the age of the cylinders, how far they have been bored, are they genuine BMW cylinders or reproduction cylinders?

It surely never occured to me that you would have porosity through the cylinder walls.

Amazing.


Mal

[corvair]

Interesting indeed! When I remove the cylinder again I'll measure the inside to see if it was ever re-bored. In the meantime I'll investigate if such a pin hole can be plugged/sealed/welded. I know reproduction cylinders are available from a US supplier.

By the way, I just had to look up Toowoomba. I love the name. I see we were "near" a few years ago when we were in Brisbane, Hervey Bay, and Fraser Island.

Best,

Michel