I worked on a car over summer that behaved as described exactly. Engine would not tolerate ANY
preload on hyd lifters. Adjusted to 0 clearance ran fine. Lifters were Comp Cams Race Hyd.
Engine was SBC. Replaced lifters with "standard" type. All is well. Cam companies claim to make
their own lifters, but I have my doubts. I think those "race" lifters were probably a run of parts
that were machined improperly in a third world country, bought at a bargain price, and
marketed as a "race" part. Waddaya think? Am I crazy?