Briggs opposed twin loose valve seat fixed finally.

[Arkie]

Was given a nice Briggs opposed twin engine, 42A707 3 years ago that was only running on one cylinder due to ex valve seat popped out.

I re-stacked the seat 3 different times over 3 year period finally got a good re-stake by pinning the seat using steel machine screws.
I've re-stacked Briggs valve seats before with fair success, but this one just would not stay in place.

Was about to scrap the engine for parts
After looking at the aluminum block around the seat I seen that it had extra deep aluminum around the outer edge of the valve seat especially in the portion where the head was dished out and I took couple of steel 4/40 machine screws, (could have use 6/32) set the valve seat in place and countersunk the block for the heads of the machine screws (the seat edge was slightly below the surface of the block then drilled and tapped so as the heads of the machine screws would just touch the outer top edge of the valve seat when tightened down and not be into the valve seat taper area. then also staked the two screws into place. Could have used 3 or 4 of the screws. The two pan head screws I installed are on opposite sides of the seat.
I then used valve lapping compound and checked that the valve was still seating ok into the pinned seat.

I was repairing this engine for use for myself, not for someone else.