vave clearance?

Discussion in 'PSI Superchargers Tech Questions' started by blutowski, Oct 2, 2005.

  1. blutowski

    blutowski New Member

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    im new to aluminum rod engines. can anyone tell me how much piston to valve clearance i need? i run a 477 BBC,< 3.75 stroke, and 4.50 bore > and get her up to about 8200 rpm. she likes the rpms, but my valve train doesnt. i keep bending valves. and on the last pass i slapped one bad, and tore the engine up pretty good. although i think it was caused by these dumb offset lifters that comp cams talked me into. anyways, any suggestions?
     
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    blutowski, Oct 2, 2005
  2. Mike Canter

    Mike Canter Top Dragster
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    Which valves are you hitting, the intake or the exhaust? Do you know what your piston to valve clearances are now? What valve springs are you using with how much seat pressure. How old are the springs and have you checked the off seat pressures recently with them on the motor?

    I seriously doubt that the offset lifters are the cause of the problem. The offset is so that the pushrods do not rub against anything. Normally required with some head and rocker arm combinations. Are all your pushrods now centered in the holes through the complete valve cycle?
     
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    Mike Canter, Oct 2, 2005
  3. Ken Sitko

    Ken Sitko Super Comp

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    I like .150 clearance on the intake valves, but you can get away with .125. You need more clearance on the exhaust valves because they are traveling the opposite direction of the piston. I like to run .200 clearance on these, but I'm not sure what the minimum is.
     
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    Ken Sitko, Oct 5, 2005
  4. flatbladed

    flatbladed New Member

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    my dad and i run the same bore and stroke 7 inch rods with brodix 2 extras in a front engine car. do you run titanium valves? maybe you valve guide clearance is to tight.the presure from the blower goes right up the guides pushing the oil out .if there to tight the valves could stick open. we run titainiun with .002 clearance @ 9200rpm in the lights and 275 lbs seat preasure. we have 75 passes with this setup it seems to be working.
     
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    flatbladed, Oct 7, 2005
  5. blutowski

    blutowski New Member

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    thanks alot guys for the input. ive been out of town for a while, and just looked at your comments. after goin though the engine today, it looks like im just an idiot. i didnt shave enough off the pushrod holes in my heads for the needed clearance of the offset lifters. the pushrods are getting pinned against the head at almost TDC. when it does that the pushrod wants to jump out of the cup in the lifter. another case of ME being my biggest technical difficulty. lol! thanks again for the input guys.
     
    #5
    blutowski, Oct 9, 2005

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