OHD
09-13-2008, 09:15 PM
When chosing a new camshaft be very aware that many of the newer agressive cams have opening/closing ramps rates that require much more PtV clearance that is considered normal at 10 before and 10 after the cam ramp apex.
The opening/closing rates of these cams can cause the valve to overtake the rate of decent or rise and clip the piston.
Some times with high spring pressures it is almost unnoticible, until startup. Then KABOOM.... (and the swearing off the use of plasticgage....:tongueflap:)
Retarding the cam sometimes cures it but most of the time flycutting is required to get the needed clearance. :grin:
Ran into the problem today with a 800 lift cam that had been "clayed" 10 and 20 over and under..
Luckily we caught it and all it took was 8 new valves, valve job, gaskets, flycutting the pockets, and some time. :grin:
The opening/closing rates of these cams can cause the valve to overtake the rate of decent or rise and clip the piston.
Some times with high spring pressures it is almost unnoticible, until startup. Then KABOOM.... (and the swearing off the use of plasticgage....:tongueflap:)
Retarding the cam sometimes cures it but most of the time flycutting is required to get the needed clearance. :grin:
Ran into the problem today with a 800 lift cam that had been "clayed" 10 and 20 over and under..
Luckily we caught it and all it took was 8 new valves, valve job, gaskets, flycutting the pockets, and some time. :grin: