Hi, I'm changing the timing chain and crank gear in my 01 polaris scrambler 500 and I'm having a hard time getting it to run now. It ran for awhile then died and hasn't fired up since. Has spark, has fuel, etc.. I noticed while turning the engine over that the exhaust valve is opening a little before TDC. I'm thinking this is not right, and I've probably overlooked something. I've triple checked my timing marks on the cam gear, the crank gear, and chain. Anyone know what I've missed?

 

Check that the spring on the exhaust valve detent lever hasn't slipped out of place. I've had that happen before,it would run,but not accelerated and die.

 

Thanks OPT, I'll check that this evening after work. I would also like to thank you for many of you'r answers you've posted on here. Although I just joined the community, I've used you'r Info. quite a bit to make repairs in the past.

 

Well I checked the exhaust detent and it was fine, so while I had it out I ran a compression test and had no compression. Next I ran a cylinder leak down test and it showed a lot of air coming out the air box so I guess that means bent intake valves. Just not sure how it ran for awhile if the valves were bent. Anyway I guess I know what to fix next.

 

Hopefully carbon build up under one or both intake valves and not bent. If you had the cam timing spot on,valves shouldn't have bent. Don't forget new intake and exhaust valve seals.

 

Been a while since I got into the valves on a 4 stroke, but make sure you check them over closely, I want to say the intake rod is steel and exhaust is Aluminum. How 'bout it OPT?

 

Intake and exhaust valves are both steel. The exhaust valves are stronger to withstand the high temps when open to expel the exhaust gasses. Same as most engines.

 

When I replaced the timing chain, I had all the timing marks where they were supposed to be, but I noticed when you turn the engine the chain marks don't match up with the cam/crank marks again until it is rotated probably 20 or so times. Made me wonder if this is normal, or if they sent me the wrong chain or gear. Any idea on that?

 

Don't pay attention to the three plated links on the cam chain! They're just for ease of cam timing only. Once you align the one link to the bottom sprocket mark,align the two links to the two dots on the cam sprocket,then is when you are to reinstall the cam chain tensioner and adjust the valves while it's still at TDC. ONCE you turn the engine over after this the plated links wont line back up with the original marks!!! Plus compression on the 500 is only from 65 to 90 psi on average because the exhaust detent holds the exhaust valves open a tad for ease of starting.

 

Thanks OPT, thats what I wanted to here!