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Discussion Starter · #1 ·
I have an 04 Raptor 660. No significant mods. It recently lost compression while I was riding down the road. I tore off the valve covers to find what appears to be a bent exhaust valve. I just want to make sure that this is what is wrong. The valve looks like it is at a slightly different angle than the other exhaust valve. Also, the valve, spring, and washer seem to be seated a little higher than the undamaged valve. I can get a feeler gauge in the undamaged valve but not in the damaged one. My question is this: Are both exhaust valves supposed to look the exact same as far as height goes? They both move up and down like they are supposed to I am just assuming that the one is damaged due to what I just explained. This would obviously cause me to lose compression. Does this sound correct? Is there anything else that I can check to ensure this is my real problem before I take it to get fixed? Thanks in advance.
 

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Your timing chain could have stretched or broke. I would pull it down and see what all you need. Could be a simple rebuild or could be alot worse then you think if it damaged the Piston, Rod and valve. Its not that bad to do a top end on. Beats paying someone to do it and keeps money in your pocket.
 

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I have an 04 Raptor 660. No significant mods. It recently lost compression while I was riding down the road. I tore off the valve covers to find what appears to be a bent exhaust valve. I just want to make sure that this is what is wrong. The valve looks like it is at a slightly different angle than the other exhaust valve. Also, the valve, spring, and washer seem to be seated a little higher than the undamaged valve. I can get a feeler gauge in the undamaged valve but not in the damaged one. My question is this: Are both exhaust valves supposed to look the exact same as far as height goes? They both move up and down like they are supposed to I am just assuming that the one is damaged due to what I just explained. This would obviously cause me to lose compression. Does this sound correct? Is there anything else that I can check to ensure this is my real problem before I take it to get fixed? Thanks in advance.
If it is as you are saying with the valve, it could have broke, this will cause all or what you are saying about the valves and what the engine did..........
Pull the head to find out........
 

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No need to pull the engine. Just the valve cover, Cam, and after the valve cover is off there are 7 bolts holding the head to the cylinder and 6 more holding the cylinder to the bottom end. I would at least pull it down to see what you are gonna need before you order anything. There is a manual in the stickys of one of the 660 sections to download for free. It will help you out. Not that big of a job doing the top end.
 

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As said, pull the head off and check for damage, if you have dropped a valve, most likely the piston is damaged and you could also have a bent connecting rod............
 

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I bought a spare motor, and the guy I bought it from told me that thengine lost compression exactly the way you described your scenario.
I tore the engine appart thinking it had bent or broken a valve, only to find out that the valve went out of adjustment.
If you had dropped a valve, you would know !! It doesn't sound like it.
My 2 cents !!
dan
 

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Discussion Starter · #8 ·
Thanks for the post Hemi. I will check that tonight and make sure thats not whats wrong with it. I can't get a feeler gauge in it and it does sit a little higher. I wouldn't complain if thats all that was wrong with it...
 

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Discussion Starter · #9 ·
So after tearing off the head, and not to mention breaking it, I found what was wrong with my quad. The cotter pin at the top of one of the exhaust valves had broken, leaving the valve stuck open and no compression. I haven't gotten it back together yet, but hopefully the valve is not damaged. How likely is it that the valves get damaged or damage the piston in these quads?
 
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