Motobecane av7 crankcase gasket issues

Alden Stover /

I'm working on a 1979 motobecane 50v av7. I had recently put in new crank bearings and seals; the replacement crankcase gasket I got from treats didn't match well, so I had to cut it down to fit, and it was very difficult to keep aligned as I struggled to get the crankcase back together. The end result, this crankcase is leaking like a sieve on both sides near where it matches the cylinder.

Please advise; is there anywhere I can get a quality, properly fitting gasket from? Is there any method to ensure it is on correctly as I put the crank case back together? As many on here know, dismantling and putting together these crankcases is a major pain in the ass. I don't want to have to do this multiple times.

Re: Motobecane av7 crankcase gasket issues

Yeah, I made mine myself with an exacto. Did you use a sealant? I put a teensy amount of yamabond on both sides of mine.

Re: Motobecane av7 crankcase gasket issues

Alden Stover /

I did not use sealant. I do have some permatex ultra grey maximum torque gasket maker, but it says on the packaging not to use with parts in contact with gas, so I was a bit nervous about using it.

It appears cutting out my own gasket is the way to go...

Re: Motobecane av7 crankcase gasket issues

Alden Stover /

What thickness gasket paper do I get?

Re: Motobecane av7 crankcase gasket issues

Richard Eberline /

making gaskets is for advanced engine builders. Also need metric hole punch set.

Good pair of scissors. OEM thickness, if you change the thickness, the fitment of all parts change.

Re: Motobecane av7 crankcase gasket issues

I had the same issue with a carb kit I got for the Gurtner on my 63 AV88. Nothing worked quite right, while it looked right in the picture in application it wasn't.

If you have to make a gasket put oil on the surface of the crankcase to mark the gasket paper and make a pattern. You can pick up gasket punches from HF at a minimal cost. I would use Yamabond or 3Bond which is the same stuff. Some of the liquid gasket material you can get from your local parts store doesn't play well with gas, read the label before you buy.

Re: Motobecane av7 crankcase gasket issues

I remember a conversation I had years ago with a guy who had been stationed in Germany after the war. He told me that instead of using gaskets on crankcases that they, the German mechanics, would use silk thread with varnish to hold it in place. Now I'm not saying to use varnish which is very old technology, but with a good sealant that is gas resistant a string of silk thread might just do the job.

Just a thought.

Re: Motobecane av7 crankcase gasket issues

sounds like its not sitting flush, sometimes it help to tap the halves together here and there with some blocks of wood to help seat the bearings in the cups, and mate the surfaces, then retighten. some people say heat as well. does your crank spin smooth?

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