So is it time to throw in the towel on this one or do you have enough spare parts collected already to build what you have? I've only seen 2 valve seats come loose. One was in a 60's model Briggs on a pushmower, the other was in my Ford grain truck. It took us a couple days to figure out why the truck was missing. Of course I assumed it was merely a sparkplug and loaded it with wheat before backing it in the shop. That was motivation enough to solve the problem!
