How do I know that my valve seal is defect and wichone ?!?

6 replies to this topic
  • steevefortin

Posted May 18, 2008 - 11:24 PM


I have a YZ450F 07 and it start smoking. So I went to check the valve and the clearence was a little our of spec and a little out of timing. Could that be the why of the smoke ? How could I tell that my valve seal are not good ?

Thanks for any help.

  • DeeCee

Posted May 19, 2008 - 01:03 AM


The normal syptom is smoking on start up which clears and doesn't continue. If the smoking is fairly constant then it is something else.

To change the guide seals you will have to take the head off so might as well do a full top end refresh while you are at it. Make sure you change all the valve guide seals as no way to tell absolutely which particular one is the problem.

  • steevefortin

Posted May 19, 2008 - 07:03 AM


thanks, it did start to smoke only when I was bliping the throtlle and not on startup... after few minutes of ride it did start smoking all the time, even on idle. According to this, it should be something else then, maybe the rings ? Would it be normal for a 2007 that rings is already bad ?

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  • intensem1rider

Posted May 19, 2008 - 07:25 AM


It could very well be normal that the piston and rings need to replaced, it all depends on how many hours are on the bike, how good of oil you use, and how often you change it. The age of the bike means nothing.

If your going to do a top end rebuild, be sure to replace the cam chain as well, and also pick up an hour meter so you know exactly when to change the oil.

  • steevefortin

Posted May 19, 2008 - 08:11 AM


I am using amsoil and I did change my oil maybe 15hours of ride before that happened. Hours meter is not a bad idea :thumbsup:

I was reading on another forum, yes that was for CRF, but it was telling that after a hard fall his bike start to smoke and smelling like burn plastic. He said his problem was burning gear oil because the bike did run on the side and burn his seal. Now having said that, I did fall kinda hard few rides before my smoking issue started... could something like that have happened to me ? I did smell burn plastic and check that all my plastic wasn't burning, but found nothing.

thanks again

  • intensem1rider

Posted May 19, 2008 - 08:19 AM


Wow, you gota change your oil 3 times more often than that! You should be changing it around every 5 hours on the motor.

My friends have CRF's and everytime there bike ends up upside down and running, they have oil come out their exhaust and it burns, I have never seen a yamaha do that, but it's a possibility.

  • steevefortin

Posted May 19, 2008 - 12:14 PM


Just to know... to book call for 1000km for oil change... do you guys change it before ?

After 3 time opening the cam cover to finaly find to good timing spot, that by the way is not totaly align with the cylinder head, the punch mark on the exaust camshaft is a little below the surface. When I was putting the mark directly align i could start the engine just once, after that the kick was lock and even if I was moving back...nothing to do. Did that already happened to one of you ?

So anyway, now that my engine work again I still smoke a lot and I will have to open and change seals, rings and gaskets as it dont smoke when he is cold, but get worst when warming up. So any tips would be appreciate on the job. Thanks

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