Clarifying an over-rev
Thread Starter
On The Tree
Joined: Nov 2007
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Clarifying an over-rev I am just a bit puzzled by how an over rev knocks the pistons against the valves when the valves are directly timed by a chain, does this chain stretch? What exactly is happening? It would be cool to find out, thanks.
On The Tree
Joined: Nov 2006
Posts: 155
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it happens because the factory valve springs cant keep with the high rev and instead of going up or down when they are supposed too, this is called valve 'float'. at which point the pistons are nice enough to make sure they are shut for you...
I believe if you over-rev and there piston to valve contact, this is a result of Valvetrain float. This occurs when a poor or stock valvetrain is revved really high and the valvetrain(lifters, pushrods, springs, rockers, vavles) can't move fast enough at high RPMs. So what happens is it floats and the valve stay open to long because the springs are not performing as well at the high rpms.
This is my take on it and I am prolly not goin to be exactly right but im sure someone who knows more will chime in
This is my take on it and I am prolly not goin to be exactly right but im sure someone who knows more will chime in
TECH Resident
Joined: Jan 2003
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From: AUSTIN TX
In short, the cam is controlled by the chain. It slings the valves open, but instead of the valvetrain (lifters, pushrods, rockers, and valves) closing when the cams wants them to, they keep opening a little farther, and then take longer to start closing creating slack in the valvtrain because the cam lobe is already closing (thus the term float). If it floats long enough, the piston already on it's way up helps close them for you.
Thread Starter
On The Tree
Joined: Nov 2007
Posts: 115
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Interesting, I was thinking about valve float too but I was kind of woundering because my pushrods got very bent and the tops of the pistons got a semicircle smashed into them.. seems like a rediculous amount of inertia for such a small part, but I guess its that because the lifters were lubed good and nothing stuck, so was it just inertia then you think?
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Just think how fast those parts are moving when your engine is turning 6000rpm. Of course the valve train is only turning half as fast as the crank, but you get the idea.
Have you pulled the engine apart yet to inspect any other damage?
Have you pulled the engine apart yet to inspect any other damage?
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