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valve hit piston why?????

B

beefy blazer

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i just built a 383 stroker, flat tops,282 [email protected] and.495 valve lift, its a solid flat tappet cam . i checked the piston head to valve clearence and it was well within specs, so why would have #4 exhaust valve have hit the piston?it wasnt a hard hit(piston is still fine) but the valve was bent which in turn ruined the seat and the brand new bronze guide. any insight or advice would be quite appreicated.
 
valve lash too tight jumps to mind. If it was too tight the rocker was pushing the valve farther off of the seat and tap a tap tap. What is "fine valve clearance" in your book? valve relief pistons? Is the cam advanced or retarded from the manufacturer specifications?

are you sure it is 282 degrees @ .050"? That is an EXTREMELY agressive camshaft with huge overlap, that likely leaves the valve very close to the piston at any given point.
 
Either something is off with your lift ratio / spring rate or timing ........... But there could be a number of other factors .... piston height, rod size different....
 
If only one valve hit, it is not a valve timing thing. The valve lash would have to be rediculously tight to cause the problem. My guess is that the valve got stuck in the guide and did not close.
 
sled_dog said:
timing belt let loose?

sorry couldn't resist
Click to expand...

It happens with chains, too. I had a Caddy lose a chain and it smacked all 8 intakes and 3 or 4 exhausts.

But yeah... if it was just one valve, then the problem is more than likely isolated to that cyl. Either a sticky valve or a weak/busted spring or something.
 
Baja Blazer is right, If it was only one valve it is isolated to that cylinder. Maybe the valve guide was not lubricated enough, or to tight to start with. I doubt it was because the lash was to tight.
 
One obvious cause that comes to mind is valve float. You didn't happen to wind it real tight, did you?
 
lifter?..

I've seen hydraulic lifters lose the little lock clip that holds the push rod cup in them,and then they pump up beyond normal limits,that can bend push rods or valves..weak or broken valve springs,a sticky valve,or tight guides can let the valve get "kissed" too,especially in motors with high lift cams and close piston to valve clearances..valve can't "snap shut" fast enough,and the piston whacks it..:crazy:
 
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