340 with metal in oil pan

72bluNblu said

I agree pictures can be misleading, but with that kind of curvature the diameter is way too small for a seat.

If it's got a "small knock" like the OP described the whole thing has to be disassembled.

Click to expand...

I think that you're correct on the valve keeper/retainer as that will fall in the crank case and into the oil pan when it fails...

If it were a valve seat, it would have fallen into the cylinder and would have beat up the piston top... I've seen that too many times... There would be many small dents in the top of the piston if the debris fell into the cylinder...