yz400f valve job.

3 replies to this topic
  • randytbo98

Posted September 28, 2008 - 12:22 PM


im planning on replacing my valves. im wondering what i can get away with. i would like to just do valves, springs, retainers, and seals. i guess im just trying to ommit guides and a seats. what do you guys think?

  • grayracer513

Posted September 28, 2008 - 06:38 PM


It is possible, but really quite unlikely that you need valve guides. The design of the head places very little lateral loading on them. Check them, though, and have them replaced if needed.

Seats will almost certainly NOT need replacement. They will need to be refinished, however. Grinding is preferred. Careful, skillful cutting is OK.

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  • randytbo98

Posted October 13, 2008 - 12:59 PM


i know its posted on here somewhere. but i am wondering about porting and polishing my head, is it worth the cost for a bike i will be just riding in trails and playing in gravel pits. also i need a new exhaust cam, ive heard about putting in the 450 cam but i was thinking about hotcams. i have no problem buying 2. will i only get a performance gain from the hot cams, or does the 450 cam have gains besides the auto decomp. sorry if im asking a question that has been asked a millon times im just having trouble finding the right answer.

  • yzhaulin

Posted October 13, 2008 - 06:14 PM


Randy. I'm going through this as we speak. My timing chain stretched and the intake cam jumped time. Luckily it really didn't damage anything. But I'm going to do the entire top end anyway, Piston,rings, wrist pin, clips, timing chain and tensioner all 5 valves and valve springs.That way I know what i'm working with.
The hot cams also has the decompression your looking for and is a bit easier to set the cam timing from what i've read on this site.
I havent posted here much but have found a wealth of information and tips from reading old posts.Especially Grayracers.
Good luck with your build.

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