HELP 99' YZ400 motor probs.

Heres the deal.

I got the bike about 2 weeks ago for a killer deal.

The bike had oil leakin at the head, base and right side cover gaskets.

So i got a complete gasket set and replaced them all, no external leaks.

So i go for a little ride and i see some coolant dripping from the over flow, i didnt think too much of it, but i topped it off and just took a bottle of water with me for a little ride to make sure all was good.

The leak out the over flow got worse and worse, until it came to the point that it would lose about half a quart every 10 minutes.

So i figured the head gasket was blown, forcing pressure in the system.

So i take it all back apart, and it was obvious that was the problem, so i lapped the crap outa the head on slab of glass and some 400 grit paper.

I used the gasket that i took out of the bike the first time i took it apart, put a glaze of high temp silicon on it (i know ur not sposta do this and that the silicon is not meant for head gaskets, but ive done it in a crunch many times on my 2 strokes) put the head on, waited an hour, then torqued all the bolts in a crisscross pattern, put the cams in, but when i turn it over with the kickstart its not right, i can get it past the compression stroke with my hand.

I KNOW the cams are in right, i probably checked it about 10 times, but the valves must not be seating right or somthing, Im STUMPED, please, anyone have any ideas??


If you can turn it over by hand you are probably right. If the cams are in correctly, check again for the 11th time just to be sure, then you probably have a valve that is not sealing. You could do a leak down test. The other way you can find out which valve isn't sealing is to take the head off and fill the intake chamber with clean solvent, if it leaks through a valve you have found the problem, do the same on the exhaust chamber. OR, perhaps there is something stuck n the valve holding it open a tiny bit. Check your compression release cable first to be sure it works correctly.

Good luck

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now