2005 YZ450 Head Cover Gasket

I have a 05 yz450f dirtbike that has about 20 hours riding time on it, its not ridden hard and it blew the head cover gasket while riding at the track.

The half circle rubber gasket on the top of the head blew out, I replaced it and made sure it was clean and torqued to specs but i didnt think of changing oil.

I ran it for about an hour and it blew once again, the same one. After breaking it all apart and draining the oil there was some coolant in the oil. Does anyone have suggestions on what can cause the "head cover gasket to keep blowing out.

the valve cover shouldn't have that much pressure in it. Make sure that the vent hose that comes out of it isn't plugged or pinched off somewhere. I would be more worried about the coolant in the oil personally. Could be a bas seal somewhere or maybe even a cracked cylinder.

Check your breather tube (the 1/2" hose coming down the left side of the frame from the cam cover). As it curves under the engine, there are two metal clips that hold it to the frame. These can get smashed flat just by brush, and then pinch off the hose. which lets excessive crankcase pressure build up. Usually, that blows the decomp bore plug out, but it you have an aftermarket one in place, the next weakest spot is the half moons.

Thanks the vent was blocked. Just waiting on a new gasket to get it back together and get it out to the desert this weekend.

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