08 yz450f

owners of 08 yz450s beware,i just broke 2 intake valves and bent both exhaust valves which in turn wiped out the intake cam, head, buckets,piston,cylinder, pretty much the whole top end is wasted and the bike is only 6 months old!!!!! i don't know if any body else has had a problem with theirs but would like some feed back on my problem and some comments on why it happend.also it is my first 4 stroke.

Look something like this?


***, umm I hope that doesnt include 07's

How much time do you have on the bike?

ho man that suck.

hope you can get it to run soon.

My '07 did the same thing at about 40 hours.

pinched the valve face off the valve stem.

usually happens because the valves lash clearance is too tight


cam chain jumps time and it hits the piston


cam gear spins on the cam shaft throwing off the timing which causes the piston to hit the valve.

make sure you replace the crankshaft w/rod and timing chain

no,its much worse.like 2 intake valves completely gone and both exhaust valves are bent.

My '07 did the same thing at about 40 hours.

it has about 30 to 40 hrs on it.

Have you checked the valve clearance in the bike since it was new?

Damn that sucks

Yammies have always treated me good

Damn that sucks

Yammies have always treated me good

x2 ::D :

Have you checked the valve clearance in the bike since it was new?

yea like 2 weeks ago, i am very meticulous about my bike and its maintenance like change oil every ride,oil filter every 2 rides,air filter every ride,even change the cam Chane every 6 months as preventive maintenance.

its CHAIN. and sounds like you did something wrong, maybe set the lash too tight. My 08 450 yamaha has over 200 hours on it, valves never moved.

Setting the valve lash too tight will not cause this. If the valve lash becomes too tight due to wear on the face of the valve, that can cause it. Valves don't always wear evenly and concentrically around the whole face, and if the wear is uneven, the valve will scrub and twist as it seats. That causes the stem to flex, and after it does that long enough, it may break.

If this is a relatively low hour bike, you might take the matter up with your dealer and see if Yamaha will help with parts on this.

After going through the same exact situation a few months ago (intake valve dropped at about 48 hours), reading posts from others who have as well, knowing what I know about the recall of the '06 250f valves and talking to engine guys, I think sometimes it's luck of the draw.

Like anything ever manufactured, there are bound to be blems. I'm pretty sure I got one and you probably did too. Fortunately for most, it wasn't the epidemic that the '06 250f was, however I would have loved for Yamaha to step up on this one.

Although admittedly, I never checked my valve clearances up to that point, if they were that out of spec to cause such a catastrophe in such a short amount of time, then something was wrong with the valve and/or head assembly.

Good luck. While you have it a part, be sure to check everything to make sure you don't end up even worse. Oh and FYI, YamahaSportsPlaza.com has the best price on heads that I was able to find. Also be sure to check Ebay.

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