Any YZ owners out there? Please help

[6 Fingered Man]

I need help, I have been through 3 head gaskets on my 04 250. The head is straight and clean as is the mating surface on the cylinder. It will not seal. As soon a I fire the bike it starts leaking coolant into the cylinder and not just a little as soon as I shut the bike down and pull the plug there is coolant on it. It will only run for a few seconds. Any help would be great I have done many 2 stroke top end and have never had a problem like this. This double o-ring setup sucks. Thanks,

[Paul_E_D]

Double o-ring setups rock! Have you actually lapped the head to make certain it's flat? If so, you're now looking for a crack in the jacket. Probably in the cylinder. If you can't find it you can get it tested...

[6 Fingered Man]

Thanks for the reply.

Cylinder looks good I do not see any cracks or issues at all. Some one on thumper talk said base gasket but could that get coolant in the cylinder? Also there is none in the oil so i doubt that.

This last gasket I put in I used some gasket maker to hold it in place and make sure it sealed and it idled ok, as soon as i gave it gas it died.

Head warped so as soon as it was getting moving it sucked through the gasket maker?

[Paul_E_D]

Base gasket has no contact with oil. Waterpump is the only place coolant can get to oil. So, base gasket could be the culprit. They do get sucked in from crankcase pressure. I think you need to take the cylinder off, inspect the base gasket, inspect the cylinder and have it checked for cracks at a machine shop, have the head skimmed while there, and rebuild with noting but a smear of waterproof bellray grease on new gaskets and o-rings. It'll be better than ever.

[6 Fingered Man]

Yah, that's where I will have to look, the gasket seal held on the head enough to pop when I moved the piston down with the head off.

Too bad I really did not want to take it apart again.

[6 Fingered Man]

Looks like the base gasket was the issue, when i pulled the cylinder off the crank case was full of coolant and the gasket was ripped. I got a new gasket kit and had the cylinder honed. I will reasemble tonight and i think it will be good. Thanks for the advice I'll update once I have the bike together.

[Paul_E_D]

Great. Make sure you dry that crankcase out good with pressurized air. You don't want rust forming on the crank...