I am trying to adjust my valves and find top dead center on the compression stroke. I have read that there should be some up and down rocker arm play on the compression stroke and no play on the exhaust stroke for the intake side. The challenge I am having is it feels like I am getting the same small amount of top to bottom play on both strokes at TDC. I also read that you can find the compression stroke by watching when the intake valve closes?

I took a video of four revolutions each stopping at TDC. Can someone please help me pinpoint the compression stroke? It appears the intake is opening and closing every stroke, is this correct? Also, when I purchased the ATV the valve adjusting nuts were completely backed out. I now have it running but it is running very rough... I appreciate any help as I am trying to bring it back to life... 2008 Big Bear 250.

 

You're making it harder than it really is. Take the plug out first so it's easier to either bump the engine over or use the recoil if you have one.Pull the recoil,watch the intake rocker arm go down. As it starts to come up you can even place a straw in the plug hole and watch the straw come up.Look on you cam sprocket. Should have a mark that aligns with a mark on the head for tdc. OR you can use the straw method.Watch as the straw comes up and as it starts to go down stop and back it up by turning the cam sprocket by hand to where the straws is at the highest piston meaning the piston is at tdc. Again you should be able to look at the cam sprocket and the marks should be aligned.Just looking at the video,looks like the pointer is at the top of the head along with the sprocket mark. At tdc both valves should have slack. If tight or too loose, adjust to specs allowed on the intake and exhaust and you're done.

 

Thanks OPT. I am able to find top dead center but my manual says I have to adjust the valves on the compression stroke. I just want to make sure I'm not adjusting them on the exhaust stroke, or does it not matter? Thanks.

 

Forget about "strokes" All you want is to be at TDC to check/adjust valves. This is where the piston is at it's highest point,both valves are closed,cam lobe pressure is off the rocker arms. In other words... TDC

 

10-4, thank you!

 

I checked my valves and they were within limits. I then did a low pressure leak down test at TDC and can feel a considerable amount of air that is releasing through the exhaust and air filter intake. That probably explains why I was only getting 100 psi compression right after installing new piston, rings, and having the cylinder honed. I guess that means I will be pulling the cylinder head. After looking at my manual it appears that there are a number of measurements for the exhaust and intake valves. Any advice on what I should look for and what may need to be replaced? Thanks!

 

A lot of the time carbon builds up on the valve seats and the valves causing the leaking. Usually all I ever had to do was clean the valves up with a fine steel brush on our work bench grinder,do the same with the combustion area and valve seats with a fine steel brush on an air drill. Then used fine valve lapping compound and lap the valves back in. Make sure the valves aren't mushroomed or have sharp worn edges. If so it needs to be replaced. Usually not necessary to have the valve seats cut. All I used was a piece of fuel line,clamp one end on my air drill,other end on the valve stem. Then I put a thin layer of lapping compound on the lip of the valve and used up and down pressure with slow speed on the air drill. I'd check the face of the valve and seat to see if it had an even clean surface on each. Not necessary to use dye. 99% of the time when I installed new valve guide seals,springs and keepers and poured solvent in the intake and exhaust port,didn't have any seepage from the valves. Every mechanic has their own way of doing this along with machinists if you have this sent out.

 

Thanks OPT. I pulled the cylinder head and poured solvent and confirmed that the exhaust had a bad leak. The intake wasn't as bad but did leak. I attached a picture of one of the valve guide oil seals. Both seals looked like this with the insides of both seals gone. Is that normal when they go bad? Also I am not able to remove the intake valve. I attached a picture where it is getting hung up. I haven't tried to muscle it. Any ideas to get it out? Will I need to replace this valve? Thanks!

 

I've seen worse on seals. Valve may have a burr on the stem not allowing it to get past the valve guide. Check for that plus it may be bent a little. If you have to,push the valve up cut the valve stem with a dremel,smooth the edges and push it out since you're going to replace it anyway. You don't wont to mess up the valve guide.