Lifter Bore Measurements

Ford 351W used a .002 clearance target. .0007-.0027 was the acceptable reading. I had a set of Hemi rollers and they were all .0005 undersized .9035...consistent on all of them when compares to a set of new SB lifters at .904. Dont know if it was wear or if the roller aspect changed the spec. Why they offered .001 oversized lifters when it was within tolerance is past me. The internals of a hydraulic lifter are super tight. When you can spec a leakdown of .0625 in 5-50 seconds with a 200psi load using no lip seals is pretty amazing with motor oil. For a manufacturer to be so loose on OD spec and keep the ultra tight tolerances on the inside is another mystery. Also there is alot of oil flowing in a motor. when you can see 10psi at idle, that means that 10psi is being maintained throughout the system, that is plenty to maintain a hydrodynamic wedge on all rotating parts, even the slow rotation of a flat tappet lifter. Your really bleeding oil at your stamped rocker arm fulcrums as they are not machined.