no compression

I reshimmed the intake side of my 2004 yz250f because they were tight and the bike was getting hard to start. I've done this many times so I'm very careful with the chain and sprocket alignment. Got it all back together and it seems like there is little compression. When I put the flywheel at tdc the punch marks are off about 2 teeth on the chain. HELP!

time for new rings and piston then!maybe new valves if u have shimmed them many times

When I put the flywheel at tdc the punch marks are off about 2 teeth on the chain. HELP!

This may be your problem. Get the timing right.

Gotta do it till you get it right. Make a mark on the chain and sprockets with a magic marker so you know where you need to be as you are wiggling the cam into position.

Good luck!:excuseme:

Got the marks lined up on the intake and exhaust cam at TDC. With the tensioner engaged the 3:00 intake mark is slightly below the top of the casing, is that right? This bike has never been reshimmed before, I checked it many times but was always in spec. 2 of the intake shims were .076 and the spec is .10-.15, now it measures .125. This bike has never had its rings and piston replaced so Im thinking that I would go ahead and do that, THANKS guys fro your help!

Should I go back with the stock piston?

Got it all back together and the bike will not start. It started before I changed out 2 of the shims, it was just getting difficult to start so thats why I decided to check the shim clearance.

I'm stooped!!!!! Still won't start! I've tried moving the cams together and seperately + and - 1 tooth but still no luck. If you rotate the flywheel 360 degrees the cams move 180. Is there any possible way that I'm off exactly 180 degrees? I thought no way because the piston would hit the valves. I replaced the piston 6 months ago put it back together and it started first kick. I've done this to a lot of bikes and never have had so much trouble.

This bike has never had its rings and piston replaced
I replaced the piston 6 months ago put it back together and it started first kick.

I'm confused:smirk:

Well regardless if you did or didn't. It was running fine before the valve adjustment...right? 720 deg crank rotation for 1 turn of the cam. That's right. As long as the flywheel mark lines up and the CORRECT cam timing marks are lined up with the tensioner installed then it's right.

Take a look http://www.thumpertalk.com/forum/showthread.php?t=564726&garpg=2 and click on the pictures to enlarge and see if this is what cam timing you are using. If that is correct then you may have a stuck lifter or a shim that's not seated. Something is not the same as it was. Just keep looking. You'll figure it out.

Edited by chris7521

Thanks Chris for responding!!!!!! It was running GREAT just was getting difficult to start. I raced the weekend before but couldn't get it started on the line that why I decided to check the valves. Again Thanks, I'll keep looking. I know one thing, I'm getting good at taking it apart!

My cams look just like the picture on the link you posted, doesn't make sense.

This is history, the bike started and it's running good!

editied: missed last post....sorry

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now