freeing up exhayst valve on 98yz400 with 13.5.1 piston

11 replies to this topic
  • whitetrashracing

Posted August 04, 2004 - 06:31 AM


do i need to pull the head or can 2smoke gas fix this with out blowing up the bike idont plan on using more than a couple of cups

  • yz426onNOS

Posted August 04, 2004 - 12:15 PM


Do you want to do it right or half assed?

Do you want to be pushing your bike back to your truck?

Just pull the head and check all measurements. Probably be a good idea to do a top end if it has been a while.

  • Jeffro426

Posted August 04, 2004 - 12:51 PM


Whats wrong with the valve???

  • SFO

Posted August 04, 2004 - 02:10 PM


Cam seizure will roll a burr into the bucket bore preventing the valve from returning to fully closed.
Investigate this first.

  • whitetrashracing

Posted August 04, 2004 - 03:03 PM


did new top end 8 hrs on motror along with new crank bearings piston etc cam is not seized nor does there appear to be anything else seized.for some reason i have a little compression but not alot

  • SFO

Posted August 04, 2004 - 07:01 PM


It looks like you have everything handled.
My mistake. :awww:
put 2smoke gas in it :devil:
you are way ahead of the game :thumbsup:

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • yz426onNOS

Posted August 04, 2004 - 08:56 PM


Ok first just pull of the valve cover and inspect the lifter buckets. Also measure the gap on the cam to lifter bucket. What type of head gasket did you use? Is the idle on the carb right? Did you check the compression with a gage?

  • YZFan

Posted August 05, 2004 - 12:34 AM


sounds like the timing could be off??

  • Hamish

Posted August 05, 2004 - 01:33 AM


I've had a similar problem with my 426 on 2 occasions. Both times it was just after I'd had then engine apart. I didnt disassemble the head, and therefore didnt clean all the carbon off the chamber. I'm guessing with mine a bit of carbon came off and got under a valve seat. Fired her up with some 2smoke gas and it fixed itself.

  • whitetrashracing

Posted August 05, 2004 - 01:00 PM


thanks to all for your help,426nos did eveything u mentioned exept i checked comp with my foot ur very knowlegebleand i appreciate your tech expertise.ok so instead of doing another teardown i mixed up some 100:1 2smoker fuel ran about 1/2 cup through motor took about 1min
turned bike off and presto major commpression so now i think hamish for his 426 prob.

  • yz426onNOS

Posted August 05, 2004 - 03:02 PM


Awesome! Now ride it like you stole it!

  • Hamish

Posted August 05, 2004 - 11:21 PM


good to hear that it worked 4 u 2 :thumbsup:

Related Content


Is it worth it? (Cam and High compression piston) by macgi77

Dirt Bike   Make / Model Specific   Honda   CRF 150/230 F/L
  • Hot  36 replies
WR Camshaft Swap Info - last post by jamesm113

WR Camshaft Swap Info

  • 0 replies

Megabomb Fitment by 288yz450

Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • 1 reply

05 yz450f not fast enough by RedeyeYZ

Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • Hot  38 replies


Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • Hot  30 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.