I was talking to a friend of mine who does Ford engines. I explained how
the lifter bores may not be deep enough on BOPR blocks to support roller
lifters. He said that pre-roller Fords had the same problem, so they used
cams specified with a smaller base circle, so the lifters sat deeper in the
bores. For those of you who's cam theory might be a little dusty, the base
circle is the portion of the cam where the valves are closed so the lifter
is riding over a perfectly circular portion of the cam (no lobe
eccentricity). If one reduces the diameter of the base circle, the lifter
will sit deeper in the bore, with less chance of popping out. The only
drawback is that the lobe slopes will be a little steeper and a new profile
will have to be generated, based on a smaller circumference. I wonder how
narrow a cam can be ground while maintaining strength and keeping a
reasonable profile, even for rollers?
Food for thought,
James J.
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