'00 WR400 countershaft seal leaking - plugged crankcase breather?

I just rode the rattlesnake enduro, a mud fest.

I rode speedsville last year in the mud as well and in both ride the c/s seal leaked oil all over the chain. I cleaned the seal last year with a film negative and it was fine for a full year. I'm wondering if the leak was caused not by a bad seal but by a clogged crankcase breather. It was certainly plugged with the 20lbs of mud that was all over the bottom of the bike.

The question is, what happens when this breater is clogged?

Will the presurized crankcase blow oil out the c/s seal?

What do you guys think?

More than likely, the seal is probably worn out. If you still have the plastic counter shaft guard on, they have a tendency to pack with mud and grass.(I rode Rattlesnake also) I guess it could be possible for the breather to be plugged, i have never experienced this though. My KX 250 2 stroke is packed with mud around the c-shaft sprocket after this past weekend.

its quite possible that a blocked breather could have caused your oil leak. Normally the valve cover gasket (1/2 moons) it the first to get blown out when you have too much crankcase pressure

Nah I took the plastic cover off. Still packed with mud like you would not believe. Got so bad I could not shift the bike.

Anyway, I agree that the half moons would go first.

I'll change the seal.


There is a replaceable inner race/spacer that will get grooved and crusty. I have made my own new ones out of 308SS.

There is also a small oring behind it that seals the id.

I usually back it up with silicone before sliding said spacer on before c/s installation.

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