'01 yz 426 troubles


Over the past couple of weeks my 426 has become harder and harder to

start when its cold. Right up unto the point where it wont start. Ive just

had a decomp cam fitted and valve clearances done.

Keeps getting oil in the bore and fouls the plugs with oil. And today i was kickin to trying to start it after a day of riding yesterday and i found there to

be oil dripping out of the front of the head where the exhaust header comes out of.

The only thing i can think of is that the rings are worn and are letting oil

through to where it shouldnt be. So its in need for a rebuild.

I hope i havent damaged a valve although it was running perfect yesterday,

once warm starts first kick with the hot start.

Any other suggestions would be great!


You might need to pull the valves. Depending on how many hours it has, you might have gone through the coating on the valves. Other then that it sounds like it is time for a top end rebuild!

when you say pull the valves, do you mean put new ones in or is there something i can do with the old ones?

You could have several things going on including rings and valve seals but you may have to pull the top end to know for sure. Pull the top end, check the piston, and have the head/valves checked. If it's never been rebuilt it's probably not a bad idea to get it done anyway. The valves could be ok to use again but they may have to reground.

Check to see if they have worn through the coating (titanium). Should be a noticeable difference in color or have someone reputable look at them. If you have Stainless then you can get them re cut. Titanium need to be replaced.

Before you pull everything apart, have a shop do a "leak down" test. That will tell you where the problems are. If it was working fine before you had the cam put in, and the problems started just after that, I would go back and recheck that work first...

I have just removed the motor from the bike. Im going to remove the head, get it checked, and while that is getting done im going to change the piston and rings while its out. I dont think the motor has ever been rebuilt and i know its not going to last forever.

I put the cam in coz i thought it would have helped to fix some of my problems. It runs GREAT when its warm, starts first time every time, just when its cold its got nothing, feels like there is no compression.

Im guessing that when it warms up the piston and rings expand filling the bore, but when its cold its loose and not sealing, hence massive amounts of blow by fouling the plug with oil.

The piston and rings are cheap, its the valves that im scared of, in australia they want 130bux each for inlet and 160bux each for exh!

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