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valve hit piston why?????

Discussion in 'The Garage' started by beefy blazer, Feb 6, 2007.

  1. beefy blazer

    beefy blazer Registered Member

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    i just built a 383 stroker, flat tops,282 degrees@.50 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.
     
  2. sled_dog

    sled_dog 1 ton status

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    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.
     
  3. SLOK5

    SLOK5 1/2 ton status

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    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....
     
  4. sandawgk5

    sandawgk5 3/4 ton status

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    The obvious answer is they tried to occupy the same space at the same time:D. Other than that I dont know but I am curious.

    Ira
     
  5. sled_dog

    sled_dog 1 ton status

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    timing belt let loose?

    sorry couldn't resist
     
  6. BAJA_BLAZER

    BAJA_BLAZER 1/2 ton status Author

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    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.
     
  7. goldwing2000

    goldwing2000 Guest

    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.
     
  8. superwrench

    superwrench Registered Member

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    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.
     
  9. MaxPF

    MaxPF 1/2 ton status

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    One obvious cause that comes to mind is valve float. You didn't happen to wind it real tight, did you?
     
  10. diesel4me

    diesel4me 1 ton status Premium Member

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    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:
     
  11. goldwing2000

    goldwing2000 Guest

    Probably not the lifters.
     
  12. merace19

    merace19 1/2 ton status

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    I have seen my share of bad cams. ground off center from where they should be.
     

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