Jump to content
Sign in to follow this  

yz250f valve-train wear question

Recommended Posts

'04 yz250f and I'm checking my valves for the first time. I've got about 10 hours on the bike, no hitting the rev limiter and oil changes after every ride.

What I'm seeing is that all of the valves are a few thousandths of a millimeter above the minimum "in spec" values.

My question is this: during normal wear is the cam/bucket gap going to *increase* or *decrease*? I don't understand the mechanics involved. Do the valves stretch from banging on the valve seats? Do the valve springs keep them from seating all the way (thus they ride lower)?

I want to know if I should re-shim since I'm so close to the minimum gap, or if I'm good since I'm still in there and should check after another 10 hours. Thanks!

Share this post


Link to post
Share on other sites

Yes, adjust your valves. What happens is the valves seat deeper in to the head reducing the clearance. If you run the bike with no clerance the heat of combustion gets to the seats and the edges of the valves running them and you need a valve job.

You can get shins from your dealer, Hot Cams has a reasonbably priced shim kit, or you can hand lap your shims on a diamond stone. It will take about one hour or less to take two and half thousands off of a shim. A diamond stone can be bought at Lowes, these stones are used to sharpen knives and wood chisels. The shims are lapped by holding them flat on the stone and making a repetive figure eight patternand mikeing the shims till the desired dimension is reached.

Share this post


Link to post
Share on other sites

Thanks for the info and advice, RockyRacer. Though, I think I'm going to do otherwise. As far as I can tell, the shims only come in .05 increments. If I re-shim right now I'll be putting myself out of spec (too much gap), whereas now I'm just barely in the "ok" zone. I'll check 'em again after some more hours and see where they're at at that time.

Share this post


Link to post
Share on other sites

if you are above the minimun " in spec value leave it" check every 10 - 15 hrs and keep changing your oil and a yr from now you still prolly wont have to change your shims

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

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

Reply with:

Sign in to follow this  

×