[Linked Image]
Isn't that a torn up timing gear where the oil pump presses against it?

The results with the substitute set of valve train parts seem to mean it isn't the valve train. Because you had pressed hard on the decompressor pin previously and it had not moved inward to reduce the valve lift, I ended up thinking the deflection must be occurring in the valve train, but you seem to have proved it didn't. If it isn't the valve train, it seems to me that either the pin is deflecting inward (valve spring pushes it harder than you did) or the camshaft is moving in some way.

How do you feel about temporarily sticking a small piece of thin sheet metal the same thickness as the distance the pin sticks up above the cam, onto the base circle say 30 camshaft degrees ahead of the decompressor, and seeing if you get a rocker bump then? Of course you couldn't do a compression test, because the intake valve would still be open, but you should be able to see the exhaust rocker bump. If it is unclear what I'm talking about, just say so and I'll try harder to explain the idea.