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mazak500

08 yz450F kick start locked up

8 posts in this topic

This past weekend i was riding. Rode all day friday and saturday. Get to the trail head sunday morning and fired my bike up. Let it warm up and when i took off it staled out. I tried to start it but my kick starter is locked up.

I was playing around with it in the garage yesterday and if i put it in gear and move the bike around on the ground then put it in neutral i can kick the bike once before it locks up again.

Sounds like the decompressor is not working.

Any suggestions on whats wrong?

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yep you are right. Took it apart today. chain is stretched and timing jumped.

Now, I checked intake and exhaust valves and they are all in tolerence. Should i pull the head and see if there is any damage? I bought the bike new in 08 and this is the first time i had it apart. Only thing i do is change oil after every 2 weekends riding, and clean air filter of course.

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If it has compression, it's very unlikely there's any reason to pull the head.

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When this happened to me a few years ago I had some piston slap (with the valves hitting in a few spots too)...How that all ties in with the timing jumping I can't explain, that's GR's department...(supposedly it all happened because of a faulty cam chain tensioner)...For all I know it was two different problems that just happened to occur at the same time??? But I'd open it up just to be sure it's all good...If the cam chain is stretched perhaps it's time to check the valves anyway, right?

DSC04322small.jpgDSC04325small.jpg

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I have also seen a cam sprocket "slip" on the cam. Lined up the timing marks proper and the exhaust cam lobes were way off.

A new cam chain every now and then is really "cheap" insurance...especially with the YZ's. I dont remember the exact cost but I think you can get 3 yz cam chains for the cost of one of any other brand.

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My 08 and 09 did this only once in a while. No timing issues. I put in gear rolled it back and forth, and it freed up. In fact it happened on my first 08 then both of my 09's. Just my experience.

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My 08 and 09 did this only once in a while. No timing issues. I put in gear rolled it back and forth, and it freed up. In fact it happened on my first 08 then both of my 09's. Just my experience.

That's a different issue, in which a sudden stall catches the engine hitting the compression stroke before the auto-decompression flyweight can extend the decomp pin:

http://www.thumpertalk.com/forum/showthread.php?p=9110763#post9110763

That's normal, but the OP stated his ran up against solid compression on every stroke after it started. That's a giveaway that the exhaust cam has slipped.

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