putting new valves in a new head

4 replies to this topic
  • thmlrmg

Posted March 23, 2009 - 05:23 AM


Hey guys I have a quick question. I blew up my head after a valve broke and here is my question. I have a brand new head from the factory. Can I just put the valves in the head or do I need to get the seats cut? Also does anyone know if the heads come with valve guides installed already?

  • grayracer513

Posted March 23, 2009 - 06:58 AM


Guides are installed, but the seals, of course, are not.

The valves should just drop in and work, but you should test the sealing between valve and seat before using the head. If any fail to seal, they can be lightly skim cut to correct this. DO NOT lap the valves for any reason, regardless of what you see printed or hear said anywhere.

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • thmlrmg

Posted March 23, 2009 - 07:14 AM


Ok, thanks. I ordered all the hardware I was just wondering about the seat cutting thing. I found on here that almost every thread when someone is replacing valves they mentioned seat cutting.

  • grayracer513

Posted March 23, 2009 - 08:48 AM


I found on here that almost every thread when someone is replacing valves they mentioned seat cutting.

Those are heads being rebuilt, not new ones. Reasonable question, though.

  • VB_Racing

Posted March 23, 2009 - 08:07 PM


After you assemble it, take it to a reputable machine shop and ask them to vacuum test the head. THis can usually be done while you wait if they are not too busy, and doesn't cost much. THis will tell you immediately the fit between the valve and seat. Like gray said the chance of it not sealing is small, but it is best to make sure. A less expensive but slightly less detailed way to check is to "solvent test" the valves by filling the combustion chamber with solvent and watching for leaks through the seat. Good luck!!


Related Content


2016 YZ450 by CaptainKnobby

Dirt Bike   Dirt Bike Technical Forums   Suspension
  • Hot  59 replies

James Stewart back on a YZ450F by YamaLink

Dirt Bike   Special Interest Forums   Pro Racing
  • Hot  47 replies

BIGBORE FOR YZ450F 2006? by Taattie94

Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • 5 replies
WR Camshaft Swap Info - last post by jamesm113

WR Camshaft Swap Info

  • 0 replies

The "going back to the other darkside" adventure... by Monk

Dirt Bike   Make / Model Specific   KTM   250/350/450/505 SX-F & XC-F (4-Strokes)
  • Hot  113 replies

Join Our Community!

Even if you don't want to post, registered members get access to tools that make finding & following the good stuff easier.

If you enjoyed reading about "" here in the ThumperTalk archive, you'll LOVE our community. Come join ThumperTalk today!

The views and opinions expressed on this page are strictly those of the author, and have not been reviewed or approved by ThumperTalk.