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Here's a basic drawing of a valve as it sits in the block.
Wes

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My apologies for repeating myself again in this thread, but Wesley's illustration helps show one reason why the edges of cam followers break off; it can follow within 2 revolutions of the motor when the cylinder head has been resurfaced beyond limits. Visualize that as the cam lobe begins to lift the valve, if there is insufficient clearance in the combustion chamber for the valve to open fully because it has been resurfaced excessively, then the valve will hit the top of the cylinder head, thus limiting it's upward movement. The cam lobe may still be at the edge of the tappet follower and thus the force breaks the edge of the follower. More often than not the valve will also be bent.

Thus the reason not to ever resurface a head unless absolutely necessary, and whenever a head is resurfaced or questionable, perform one of several tests to make sure you have enough clearance for the full valve lift.

PS: Of course that's not the only scenario that would result in a cam follower breaking at the edge. Another would be a valve frozen in it's guide.

OD, your post made me think of this one,packardclub.org/forum/viewtopic.php?f=6&t=2734