valves hit piston why??

Hello, I got a 2005 YFZ450, i took the head off and i seen that one intake valve broke right off and the was hitting the piston. I was wondering what would make the valve hit the piston to break off the valve? or is that even why the valve broke? Any info would be great....

Thanks

timing chains prob wore out

If your timing is out enough the valves will hit the piston. On my dads truck, we were out by 5 teeth, and we bent all of the intake valves, all 4 of them (4 cylinder), so timing is very critical.

Or, if the timing was correct, and you are running stroker cranks without any spacing, then you could have rammed your piston right into your valves.

Lots of variables..

Or, you over revved it and floated the valves causing one to kiss a piston.

if my timing was out 180 would the valve hit the piston??

I think so, it would mean that the valve would open as the piston nears the top, I think.

If your timing was off 180 degrees, your quad would crank until the piston hit a valve. I don't know if an electric starter would break a valve, but a kick starter will. There's not much chance it would run with the timing that screwed up. You'd probably blow a head gasket if the valve were in adjustment and seated good.

i still think the chains wore out

yeah i was gonna put a new chain in it.. think i should also change the tensinores??

yfz's are notorious for top end problems. fix it right the first time, including new valve springs(kibblewhite's) and the oil squirter mod.

there were 2 types of yfz's made during the 04-05 production runs, reliable ones and unreliable ones. my buddy had an unreliable one and after several grand spent on a couple rebuilds and it never wanting to start he got rid of it.

yfz's are notorious for top end problems. fix it right the first time, including new valve springs(kibblewhite's) and the oil squirter mod.

there were 2 types of yfz's made during the 04-05 production runs, reliable ones and unreliable ones. my buddy had an unreliable one and after several grand spent on a couple rebuilds and it never wanting to start he got rid of it.

:smirk:

:smirk:

oil squirter mod?

timing can't be off "180" on the yfz's it uses a wasted spark during exhaust stroke. If your valve timing is right to each other and to the crank then it's right.

I would look at the timing chain, chain tensioner, connecting rod, and connecting rod bearing issues. Also you have to ensure that the valves are checked often to ensure they are within spec.

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