Flat tappet hydraulic lifters have the foot of the lifter ground on about a 50 inch radius, so they are slightly rounded on the foot. This, together with the uphill grind on the cam's lobes, causes lifter rotation which keeps the lifter/lobe working with each other. Problems arise when the lifter fails to rotate and the cam begins to eat the foot of the lifter. The lifter goes first, then takes out the cam lobe. You can hold two new lifters together end to end and you will be able to see the radius. If there is no radius, the lifter(s) are toast and the cam is not far behind. The problems with flat tappet cams began when the oil companies stopped adding extreme pressure lubricants to the off-the-shelf motor oils. They did this because the auto manufacturers were having an excess of warranty claims due to clogged catalytic converters. Apparently the extreme pressure cam lube in the motor oil was doing the damage. Well, as you can imagine, as soon as extreme pressure lubes disappeared from off-the-shelf motor oils, we began to experience lifter/camshaft failures. This tutorial that I wrote several years ago will explain it better than my long-winded explanation here......
http://www.crankshaftcoalition.com/w...ips_and_tricks

Most of us have changed our way of doing things, opting for hydraulic roller cams in our motor builds. Roller cams require only off-the-shelf motor oils and require no break-in.

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