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302CI Build - What's Your Problem?

The other option would be to convert your early small-block to accept the later factory roller cam and lifters. It's actually not that difficult. Comp offers a retrofit kit (PN 31-1000) that includes a factory-style retainer to hold the lifter guides (also included) in place; you just have to drill and tap two holes in the lifter valley as per the instructions. Ford-style roller lifters (also available from Comp) are intended to be used with this kit and will drop right into the lifter bores in your '69 block. Make sure to use the roller-specific camshaft thrust plate and not the original one from your engine if you opt to go with the roller-the early nonroller piece is not hardened and will be galled by the steel roller cam. If you perform the conversion, you can slip in a stock 5.0 H.O. roller cam or step up to an even stouter grind, such as Ford Racing's E303. Just remember to check that piston-to-valve clearance.

Are All Valvesprings Created Equal?

Keith Tolleson, Bowling Green, KY: I'm in the process of acquiring parts for a 454ci big-block Chevy that I intend to put in my '92 Chevy pickup. I want to use a hydraulic roller cam (I'm looking at Crane's PN139021 with 0.610/0.632-inch lift and 234/242 duration at 0.050-inch lift), but I think there are specific valvespring requirements for rollers. Recently, I came across a set of AFR 265cc oval-port Magnum heads. Will I be able to use the springs on these heads or will I have to buy the Crane-recommended springs (PN 99896)?

Urik Ulick, Crane Cams Phone Tech: When considering springs for any application (and especially for hydraulic roller cams), seat pressure is critical. Proper seat pressure is necessary to ensure the hydraulic mechanism does not pump up and create a slight internal vacuum leak due to the valves not seating at the proper time. Higher seat pressures are also necessary on hydraulic rollers as compared with hydraulic flat tappets because the hydraulic roller lifters are heavier and generate much more inertia.

Crane specifies a seat pressure of 150 pounds for the cam you have chosen. Air Flow Research builds these heads with springs installed at 140 pounds of pressure. The 10 pounds probably will not make much difference on the street, but to maximize performance, you might want to install a 0.015-inch valvespring shim under each spring to bring the pressure close to 150 pounds. Any competent machine shop should be able to remove the springs, check the installed seat pressure, and shim them as necessary to achieve the 150-pound recommended pressure. Be sure to check that coil-bind does not occur before maximum lift. At full lift, there should be a minimum of 0.060-inch extra travel in the spring before coil-bind occurs. Also, check to make sure you have adequate retainer-to-seal (guide) clearance at max valve lift; proper clearance is 0.100-inch minimum. If necessary, you might have to have the guides cut down slightly to ensure this clearance.

Finally, check your valvespring open pressure at max lift. Crane calls for 460-480 pounds of open pressure with this cam. Most hydraulic roller cams are made of induction-hardened or carburized steel. Spring pressures up to 550 pounds/open are safe with induction-hardened steel cams; carburized steel cams (usually identified by copper between the lobes) can handle much higher open pressures. Your cam will generate around 480 pounds at max lift. If the springs on your AFR heads can be shimmed to the correct seat pressure and have enough travel to handle the 0.632-inch lift, use them. If they do not measure up to any of these requirements, buy the springs recommended by Crane.

One final thought: Cast-iron, flat-tappet camshafts cannot tolerate the high valvespring pressures required for roller cams. Maximum open pressure for flat-tappet cams should be kept under 330 pounds (after break-in) for adequate long-term life.

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