Along with the use of assembly lubes, break-in oils with ZDDP (Zinc Dialkyl Dithiosphate), and a lifter bore grooving tool our shop does this; on all flat tappet cam engines our shop has added one step before final assembly.
With the block in a bare and clean state we’ll put in the two end cam bearings and install the cam with only light oil. Next we install the lifters with only light oil. Install a bolt in the front of the cam and spin it quickly clockwise with a speed handle and observe each lifter’s spinning action when the engine is running. You can use a felt pen to mark the lifters so it’s easier to see them spinning. If you find any of the lifters not spinning, this could be a potential problem if it leaves your shop like that. Lifter bore or even cam bore alignment could be the problem.
Many times the cam bearing bores get closer (fall) towards the crank centerline going front to back, (especially on BB Chevys) which in turn causes the taper on the cam lobe to be lessened towards the back of the motor. Zero or too little taper can keep the lifter from spinning, and this can cause the cam to fail shortly after fire-up.
To remedy this problem without reboring lifter or cam bores check local listings or the internet under custom cam grinding to have the cam reground with more taper grind into the lobes. After regrinding we do the test again. We’ve had great luck and no flat cams when all of the lifters spin before we fully assemble the engine, even with today’s lousy oils! Yes this will cost more, but what will really cost more – an extra cam grind, or a flat cam, or a comeback and angry customer? Thanks and good luck.
Norm’s Auto Machine
Engine Builder Staff
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