Piston slapping valves...

[RaceinCircles]

So my quad had a tick to it since we rebuilt it with a Wiseco 11:1 compression 85.5mm piston and rings. I read on here to adjust the valves, so I did that thinking it might help but the noise remained. I have ridden it with the tap for a while but just the other day it had gotten considerably louder and then right at the end of the day it quit running. So I tore her apart.

The first thing I noticed was on the cam chain side of the head there was some metal scraping near the top...Then I grabbed the cam chain and it had just a bit less than a pinky width of play between the sprocket...I know that's terrible. 1)How does this happen?

Then I took the head off to see the cylinder and sure enough, the piston has been scored from the bottom of the exhaust valves tapping it. Not the intake though. I was wondering what causes them to hit? Did I jump time? If I did jump time..why is my cam chain so loose?

Thanks in advance for the answers!

[greenblood01]

When your cam chain goes bad it will cause a ticking, it will be louder than your valves being out of adjustment. If you have a manual, it should show a way to measure your cam chain slack to see that it is in spec.

[droppedmazda]

hey is the piston still in the bike and if so which way is the arrow pointing? if u put a wiseco piston in backwards the piston will hit the valve enough to sound like crap and show valve marks in the piston. the arrow should be pointing towards the exhaust.

[RaceinCircles]

hm..I hope its not been in backwards! I will feel like an idiot... but Yes it's still in and I'll check tomorrow, thanks.

[Mikeman1]

If it was in backwards make sure to check it CLOSE for a hairline crack.

[buck440]

make shure you take care of it right or it will look like my piston :eek:

[RaceinCircles]

Arrow is towards exaust...any other suggestions?!

[400thacker]

I had a very similar problem...
make sure that when you install the cam chain and tentioner, that you suck the middle of the tentioner in because if you just start the bolts and tighten it up, you will cause pre-mature chain wear and stretch it and jump time and valves hit piston and wears the tentioner out so on and so on. I had to buy a new chain and tentioner because of this little newbie mistake.

[RaceinCircles]

How exactly do you suck it in like you are talking about?

[jcs003]

your cylinder may not be bore-matched to your piston/rings.

[BERT306]

Originally posted by RaceinCircles
How exactly do you suck it in like you are talking about?

get yourself a manual and it shows how to make a tool in there.

Or just use a small screwdriver and turn the small screw clockwise and it sucks the punger in. hold it like that and install the tensioner then pull the screwdriver out.

[RaceinCircles]

Cylinder was bored perfectly...

Thanks bert, I'll have to find a manual somewhere to check that out

[the Z Man]

I found that if you use 2 small screw drivers you can first loosen it with one and then stick the other one in beside it and it will hold it in place til you get it tightened..:D

[Exrider434]

Originally posted by buck440
make shure you take care of it right or it will look like my piston :eek:

hehe or mine :eek2:

[RaceinCircles]

So... What is the strongest/best cam chain to buy?

Also, Does anyone make an aftermarket cam tensioner or should I stick with stock?

[rob_990]

crf 450 dirtbike chains the strongest. i dont think there is an aftermarket tensioner

[RaceinCircles]

Got her all put back together! crf450 Cam chain is awesome. Hands down.

My piston was fine, no fractures anywhere. Got a new set of 4 valves from a guy around here that immediately tore his motor down for $15!! My cam chain guide on the front side of the motor was torn to pieces...and my oil smelled horribly of burnt rubber..haha :D I'm sure I was a noob the first time I rebuilt it and just threw the tensioner back on...live and learn right?!?!

I got to go throught a bunch of the motor I never had before..so that was fun!

Anyways, just an update and Thank you all for the help!