04 yz450f Timing chain jumping!!!!!


i have a 04 YZ450F, just did exhaust valves on the bike, set timing up, took it out riding, and i was riding like a old lady,

last couple of days the timing has jumped on the bike, than will not start,

i reset the timing than runs, timing jumps again after riding it for about an hour, reset the timing and goes again,

i have not replaced timing chain,tensioner and guides,

has anyone had problems with the chains stretching, or a faulty tensioner?

do the cranks crack on these bikes or bottom timing gear worn,

i am lost, please help

If the bike was running fine before you pulled it apart more than likely it has not gone back together correctly. Strip it back down, start again and follow the manual, be thorough. Thats just what i would start with.

When you take the cylinder head cover off, is the timing chain loose?

There are 4 basic things that cause the timing chain to skip.

> The most usual cause is camshaft seizure, usually the intake. This in turn is brought about either by oiling problems, or more often, incorrect retorque of the cam caps. Look for evidence of this on the camshaft, head and caps.

> The chain either very worn out, or kinked. Kinking is generally associated with a weak tensioner.

> Worn crank sprocket. Caused by running a worn out chain too long. If this is the culprit, both cams will be out by the same amount.

> Weak or worn tensioner. This is fairly rare, but occasionally, a tensioner will feel as if it has little or no spring tension. Even more rarely, they can be made to skip back in by pushing on the plunger. By design, the housing should break before that happens.

We keep saying it's extremely rare, but the "faulty cam tensioner" issue sure seems to keep popping up...Please let us know what it turns out to be...

We keep saying it's extremely rare, but the "faulty cam tensioner" issue sure seems to keep popping up...
It's been more common since the '06 models came out. There was a redesign of the part at that point. The earlier tensioners were very robust. If anyone has one that has actually failed, I would like to see it.

I had mine replaced, didn't hang onto the old one though...I did inspect it (well didn't really inpsect it carefully, but checked it out) and it was just wierd, there was just no "spring" to it...The top mech, Pat, at Del Amo (used to work for Factory Honda) couldn't explain why it was like that or what caused it...Didn't appear to be broken or anything just had hardly any tension...I was thinking it's just crappy springs, or ones that lose springyness if overheated...:lol::excuseme:

Yours is an '07, which is a part of the '06 and later group I mentioned, and that is the same problem that's been reported with that design. I tend to believe that the springs in them either break at the point where they are anchored, or otherwise become disengaged from the anchor point, not that the springs loose any tension.

But here again, I've never seen an older one do that.

yea who knows, i personally am discusted with this bike, i wish i had never bought it to begin with, 2 strokes are way better, atleast they run,

yea im gonna pull that thing apart again,

im just gonna order tensioner, guide & chain , fix it and let anotehr man have the head ache later on

too high maintainence for me, rather ride than push my yamaha everywhere

do i have to pull the head?

the tensioner seems to be fine, i twisted it back and holds, than releases and cant move by pushing on it

thanks for the info everyone :excuseme:

do i have to pull the head?

...to replace the chain? No.


One reason you might have to is if you improperly torqued the cam caps (too much torque, torqued out of sequence, torqued unevenly), and caused a cam to seize. In that event, the head may be damaged and need repairs. They almost always are repairable, though. The cam will likely need replacement if that happened.

i had the same problem on my 450, the chain had stretched i compared the old with the new and the old one was 1/4 inch longer than the new one, i replaced it and the tensioner and everything has been great

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