Treejumper

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Well i finally found out why my bike wouldnt start. The timing chain has more slack than a troll on DRN. :p This will be my first try and hope to do it right. I had a friend go through the steps with me tonight and will be doing it on my own tomorrow if the shop has the parts. I'll post a picture of how much slack was in the chain this weekend. Looks like it was 4 teeth off. Wish me luck!
 

Treejumper

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Here's the pics. I didnt get a chance to hit the cycle shop and they are closed til tuesday.
 

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mxer842

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Nov 11, 2003
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Is your timing chain worn or is it the tensioner? Seems kind of odd to have a timing chain wear that fast without some kind of malfunction on the tensioners part.
 

YZ165

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May 4, 2004
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:ohmy: That can't be right! I would suspect the tensioner has some issues. If the chain was streched that much, I think the teeth on the cam gears would be hammered. From the pics they look fine. I would also check the valves to see if they are bent. :yikes:
 

Treejumper

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Valves are fine and right within spec. The teeth on the cam gears are good and the tensioner is working perfectly (first thing we checked when we saw the chain loose). Actually its in all the way and pushing the chain about quarter of the way in. When you try to line up the chain on the teeth you can tell it just doesnt line up quite right. Hopefully the shop will have one tomorrow so i can tell forsure. My guess is i got a cheapy chain or lowering the gears alot is wearing it out faster?
 

YZ165

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May 4, 2004
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So the timing chain has been replaced in the past? And "lowering the gears alot"? You mean downshifting? If you're downshifting hard enough to cause that, I'm not letting you ride my bike!
 

Treejumper

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LOL! No, by lowering the gears i meant i went from a 15t front sproket to a 13t front. :) I've never replaced the timing chain on this bike.

When i stopped by the shop today to order the chain the guy went "wow" when he punched it in. I said "i guess that means it costs alot?" He replied, "No, $13 but this will be the first timing chain we've ever ordered for a YZ450F." Guess i should feel lucky. They also didnt know why it stretched so fast.
 

YZ165

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May 4, 2004
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Strange?!? I've never seen any YZ400,426,450 do that. You got me man. If you figure it out let us know. Good luck.
 

Rich Rohrich

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Chuck - Make sure and measure the distance between a grop on pins on the old chain and compare it to the new chain. I think you'll be surprised at what you see. ;)
 

ben.handasyde

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Jan 28, 2004
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speaking of cam chains it says in the 2003 yz250f booklet that if the Timing chain is stiff/cracked replace the timing chain and cam shft sprocket as set. what are cam sprockets?
 

YZ165

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May 4, 2004
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kelseybrent said:
My XR400 cam chain was $80, ouch. You could run 6 of them wide for that price ;)

Is that a 520? :laugh:
 

Treejumper

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Rich Rohrich said:
Chuck - Make sure and measure the distance between a grop on pins on the old chain and compare it to the new chain. I think you'll be surprised at what you see. ;)

Will do! Now you got me wondering what i'm going to find. ;)


what are cam sprockets?

The cam sprockets are the toothed gear looking thing under the chain in the picture. There are 2 of them showing in the picture on my YZF.
 

Treejumper

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Picked up the new chain today and measured the distances between the pins. The old chain is just a hair short of being a 1/16" longer per link. So that would add up pretty quickly. I'm doing the swap tomorrow so i pray i dont screw it up. :)
 

Treejumper

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Well i got it changed and everything worked out great. It fired up on the first kick, well that was after i remembered to turn on the gas. :)

Here is the old and new chain. The old one was very stiff and didnt want to bend at the links.

19791Chain1-med.jpg


19791Chain2-med.jpg


19791Cam_gears1-med.jpg


19791Valves-med.jpg
 
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