Dropped a valve in my driveway today

'07 YZ450F

Getting ready to ride today and was checking my oil level..was a little low so i added, started the bike, revved a few times, checked again, added a bit more oil, THEN went to start the bike and couldnt get the kickstart to even move...I kept trying and finally got the engine to turn over a few times, but no fire, and an insane amount of compression buildup..

Tried to pull the bike off with my buddies fourwheeler but even in fifth gear the compression was building up so much it would only scoot the back wheel down the road.

I know its a compression problem because i took the plug out and could easily push the kickstart down with my hand repeatedly with no odd behavior. SO..im assuming i've dropped a valve or two and they're stuck shut..either that or my auto-compression lever under the valve cover has broken...Rather than tearing into the valve assembly myself, i took it to someone to have them look at it for me, so i should know soon what the problem is... :thumbsup:

This ever happen to any of you guys' scooters before???

This sounds a lot more like the cam(s) skipped time. Pull the cover and check the timing. If you find it in error, replace chain and the tensioner.

If you bent or broke a valve then they won't stick shut, they would be stuck open. If you can turn it over by hand with the plug out then there is nothing mechanically binding either. I agree with Gray, pull the valve cover and see what's going on.

Honestly i hadn't considered that...thanks guys

You hit the nail on the head Gray...tensioner failed and skipped time about 3 teeth..so im replacing the tensioner and chain..throwing rings and valve seals in there while im at it..

haha this grayracer should change name for graygod.

hard to find a guy that through the internet can actully tell you what you got wrong!:p

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