[olddog]

Breaking in a cam, has alway seemed like voo doo to me. I'm hoping someone can really tell me what the heck there is to break in.

My way of thinking:
Since the lifter rotates in the bore, the bottom of the lifter must be flat, or it will quit rotating. Hence the name flat tappet. So there is nothing that needs to wear to a perfect fit here. Likewise the cam lobe should be the shape you want. Now neither the cam lobe nor the lifter bottom are pieces that are hard to machine.

The only thing that could possibly require being worn until properly mated would be if the lifter bores in the block are not perpendicular to the cam bore. And I have heard of the lifter bores being off enough the throw the valve timing off by 3 deg, but that doesn't mean they are not perpendicular. However if this were the case and since the lifter bottom has to remain flat in order to rotate, then the cam lobe must wear to the angle of the lifter bore missalignment. If this was the case then the lifter would need to be harder and have a rough enough surface to wear the cam. Then once the cam is worn to fit the lifter needs to smooth off and quit wearing the cam. This is crazzy. Just machine the block right to start with.

If the lifter bores were not perpendicular to the cam bore wouldn't the roller lifters have the same problems.

I guess I'm back to - I do not buy the claim that failed cams are caused by improper cam break in on start up.

If I'm full of it, please explain it so I can understan it.