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Discussion Starter #1
New here, so please be gentle. Have an 04 ATP500 with suspect worn exhaust lobe on cam and worn exhaust rocker. In the process of tearing it down to replace and I can't seem to get it to stop at TDC...wants to roll right past the mark no matter how slow I go. With that said, if I do manage to get it stopped on the flywheel TDC mark and start to loosen the cam sprocket bolts, I worry that it will move off TDC. Any suggestions/tricks to help with this?

Thanks!
 

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Welcome to the forum.
Most of the 500's ,do this, that is about the spot where the counterbalancer starts working and pushes the crankshaft .
If you are sure about your tdc mark-via the inspection plug, then you may want to scribe a mark on the engine case ,where the pointer mark is, then remove rope pull case, and line up tdc mark with your case mark,and hold the flywheel in place with a strap.
After you've put your cam gear and chain in, be sure to rotate the engine by hand a couple times BY HAND WITH THE CHAIN TENSIONER ENGAGED(it does make a difference) and double check your timing and cam marks line up.Sometimes with a lil chain stretch, you'll need to move the cam back one tooth.
Should start right up
 

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Welcome to the board!
 

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It's not a big deal if it moves around a little while you take it apart. Just be sure that everything lines up as it's supposed to once you start putting it back together.
 

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Discussion Starter #6
Figured it out

Thanks for the replies. I figured out how to do it not long after posting. I pulled the PTO side cover and wedged behind the clutch drive with wooden shims when I got lined up on TDC. Got everything apart and the cam lobes don't look too bad, but the exhaust rocker arm had some scarring. I bought a forged cam and exhaust rocker arm that I will try to put in over the weekend.

I suspected cam issues because it had been running rough near idle and started backfiring and lost power under throttle while riding it last week, then would hardly start, coughing and blowing smoke. It almost sounded like it had jumped timing or something.

I will double check everything when I get it back together to make sure my cam sprocket and chain are okay and everything is in time, valves are set at proper clearance and timing.

I bought this ATV used from a kid that didn't take care of it...I doubt the valves had ever been adjusted.

I'm an old (mid 50's) 2-wheeler off-road racer and went 4-stroke in the mid-90's...caught plenty of grief from the 2-strokers back then. Worked on cams and valves plenty back then...but that was way before reading glasses and backaches!

Thanks again!
 
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