Hope this is advanced tech worthy...

I'm wondering how a piston comes in contact with a valve... Why does over revving an engine cause this to happen? I can see bearings going, but i dont understand how components come in contact with other components like that..

Can someone claify?

 

Most of the time it is because the valve springs that are in that given application are not adequete for the high rpms. Therefore the vavle will float and hit the piston and cause some major damage.

 

To go into a little more detail, "valve float" occurs when the lifter is not held in solid contact with the lobe of the cam by the pressure of the valve spring.

At higher rpm, if the momentum of the valvetrain components exceed the ability of the valve spring to keep the lifter in contact with the lobe of the cam, the lifter may "launch" off the tip of the lobe, momentarily opening the valve farther than intended. This is one way that a valve can come into contact with a piston.

The valves may also slam shut and "bounce" back open at an inappropriate time, coming into contact with the piston.

 

Another way would be if you invite , have a get together with your club as you assemble your rotating assembly (downing a few cold ones) . You somehow install the timing chain and gear with the dots in the wrong place . Your timng would be off and a valve would hit the piston . but I don't know of anyone that has ever done that.

 

I had a local shop bring me a set of heads where all the intakes were bent flat to the deck surface, now this was on a rare set of factory 2.02/1.6" "turbo" castings, I told them that it looked like the cam was timed incorrectly..."oh no can't be that, we just put in a new cam and degreed it, everything is fine there" So I said ok and replaced all their intake valves, to shorten the story, they came back 2 MORE times after that to have valves replaced before I finally convinced them to fix their cam. LOL