Sealing the Crankcase

[brooksds]

So as I continue my quest to stem the flow of oil outside the engine... :-p

I have a small leak from the bottom of the crankcase, right along the seam. I figure no problem, I'll pull the engine and replace the crankcase sealing gasket. This will give me the opportunity to put a whole new gasket set in the engine, which I wanted to do anyway.

So I'm about to order an engine gasket set, and notice there is no crankcase seal listed. I bust out the service manual, and sure enough, no crankcase seal is shown in the blow-up.

So if these two halves of the case fit so well they don't need a gasket, what is the best method to patch an irregularity in the case seal?

[AdminGuy]

wow... I personally can't imagine putting an antique engine together without the use of yamabond 1104. Elephant snot- whatever you want to call it. I personally would steer clear of gaskets where indicated - from talking to someone (not me) who has built many of these engines..... and ridden them. my two cents.

[brooksds]

AdminGuy, thanks for the post.

Steer clear of gaskets because...

The old-style ones don't seal well?
They don't last long?
All of the above?

[MJW]

I used Yammabond on the case halves of my 51, so far it doesn't leak a drop! mike

[bmh]

Yamabond is a real S.O. B. to get back apart down the road. A mechanic glued the cases on my 71 together with it in the 80's and a few years back when I went through the bottom end I thought we were going to crack the cases to get them apart. That was after I finally got the case studs out wich also had gotten glued in place. These days I use HYLOMAR on the case halves. It stays about as tight as yamabond as long as the machined flanges on the cases are in real good shape. The factory is using some new stuff thats supposed to be pretty good but I haven't tried it yet.
Brian

[AdminGuy]

surfaces are not as tight. Modern sealants are good. Some parts require a percision fit in regards to off-set distance. ie- oil pump gears and cam cover. So you need to be aware of the whole picture.

Alot of machines leaked like.... well seeped oil when new. Modern sealants are helpful.

If you smear with finger one side and lay a piece of dental floss into the seam, you can pull it to split the cases if need be. Makes life easy. Well, any nylon string. Strong stuff.

[portagepan]

What about using nylon fishing line? I use that to hang stuff overhead that I walk under everyday, and haven't got bonked in the years I've used it.
Mike

[Kojack]

The thread trick is an old one. It helps give a little extra compression to paper gaskets and was also used to keep all of the old hardening type sealers from squeezing out of a joint if no gasket was used. The problem here is that when the crankcases are bolted together they form a structural element and you need a good tight joint to prevent them from walking or fretting against each other. I’d avoid the thread trick on this kind of joint. Yamabond and Hylomar are both old and proven sealers for this application. I don’t care for silicon sealers, I’ve seen too many instances where little silicon balls clogged an oil system.

[T. Cotten]

Ever wonder why cases tend to leak at their bellies?
Panhead carbs aim up in the air when on the kickstand, and their petcocks are notorious. Please test any candidate sealer in your local fuel blends before committing to any of them.

Avoid any thread that would not crush to allow the cases to tension upon each other for rigidity.
Un-spun dental floss sounds good; Silk thread is optimum, but even that won't straighten out a warp.

Inking and scrapeing to mate the cases can alleviate a lot of grief. Coarse grit lapping will quickly display the contact pattern dramatically.

....Cotten

[bmh]

Hylomar is rated for submersion in modern gasoline blends. and it comes back apart easy.... no strings attatched. But as I stated the machine work on the joint faces has to be true and in good shape .
Brian