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Discussion Starter · #1 ·
Guess I may open a bag of worms here with people....but what the heck.

Something I found VERY interesting while doing the valve adjustments today. I'm not sure if Randy, Kentz or someone else cares to toss in your cookies....but. Has anyone ever noticed how far off the cam timing is on atv's ?? I would guess...mine was at least 7-8 or more degrees off where it should be. I've always degreed my cams on the sport bikes and seen postive gains in HP. Now for those who are not catching the drift.

Ideally you want the intake valve to start opening at the precise moment the piston passes TDC or top dead center. This will allow the absoulte max air intake possible. If "like my case" your piston is already heading down before the valve opens you don't get the full stroke of air into the chamber resulting in losses in HP. Mine is "retarded" which means is trailing the piston as it makes it's way back down. I'm curious to see who has done their valves and noticed your top cam sproket does not match up when you align the timing mark on the flywheel. I plan on fiding exactly what the difference it is and working on either modifying the stock sprocket...or possibly implementing an adjustable unit to see if we can get some gains in HP.

I don't have an ATV dyno here that I've found yet....but would like to get base runs...then after the adjustments see if we can net a few extra HP by simply improving on the poor build that the factory does.

Anyone have a stock cam sprocket they could ship me for cheap?

Randy....what's your though...have you seen this?

Mike
 

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Mine was off too, I put it back were it was at during the reassembly so that I would see what just my mods did for me. I was plannin on going back to the dyno and degree the cam in and see whats what but I havent ordered any "dyno" tires yet.
 

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Unless someone has a way to prevent chain stretch it going to happen. If you add heavier valve springs for bigger cams it just gets worse. The chain on the 700 looks weaker than the 660.There are some heavier duty chains for the 660. I will check up on the 700 chains.
 

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Maybe due to the fact its a large capacity single cylinder a small amount of valve overlap is a good thing for exhaust gas scavenging??

How far were they out?
 

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size12 said:
Maybe due to the fact its a large capacity single cylinder a small amount of valve overlap is a good thing for exhaust gas scavenging??

How far were they out?
Valve overlap is a cam lobe function not angle. From the factory anyway. Tuners may tweak the angle, but it should ideally be at zero from the factory.
 

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Discussion Starter · #7 ·
Now ...did you guys set your valves using the TDC mark on the flywheel....or did you line up the cam sprockets? I didn't see any difference when I tested both...so I just used the flywheel. Ya know I don't really dig the raptor valve set up. The way they start and then "ROLL" onto the valve makes it weird adjusting the valves until you really think about it. They are easy...but could be confusing since it's a dynamic engagement.

M
 
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