So i recently had a misfire/loud ticking problem. I took the car to a shop and when they removed the heads, they found that my intake valve had tapped my piston enough to leave a small mark. When we pushed on the valve springs, every one would compress beside the valve that had tapped the piston. I have an 02 zo6 with headers and a cai. Does anyone know what could have caused this?

 

Stock springs and cam ?

looks like time for a spring change.

 

An over rev from a missed shift or the springs may be too weak to control the valves at high RPM. You need to do blow down on that cylinder (might want to do them all) to see if the valve bent especially since your heads have the lightweight valves.

 

I've got an '01z (heavier valves) that I discovered had the same thing you mentioned on one piston top. I was worried if the piston/valve was hurt so I called a buddy that works for a well known speed shop.... he said he sees that a lot on these engines and he said don't worry.

Mine was just an eyebrow about an inch or so long. I know I've never over reved so the previous owner must have done it.

He said that if I wanted to quickly check the valve and how it seals, he said that I should move the valve up and down in it's guide and if it moves silky smooth and doesn't bind it's not bent at the stem. Then to check the sealing on the seat.... assemble that cylinder again (springs, etc), turn it upside down on the ground, and spray WD-40 into a little puddle in the combustion chamber that covers the valve(s) in question. He said to note the level of the fluid and leave it for an hour. If the level has gone down then I should have a valve job done.

As for the piston top, he said just get some sandpaper and take off any edge or point that may become a hotspot with hard driving and possibly lead to preignition. He also said not to worry about balance. The metal is still there, just compressed.

Hope this helps.

 

Sounds like a bent valve. If that's the case then it may not be rebounding properly after the cam lifts it therefore hitting the piston and being "knocked" back to it's seat. Refresh the heads at the very least.

 

Thank you all for the helpful replies. The heads are disassembled and will be cleaned up and having new dual springs installed and a new intake valve.