Anyone ever have a valve seat drop out?

[Undercover87T]

Recently drove 100 miles round trip to a show without issues, then stopped for lunch. Went to start it after and it was knocking and down at least one cylinder for about 5 sec then shut off. Changed the coil and module for new parts which I was going to replace anyway, but it never did restart. Had to take the ride of shame on a tow truck. Valve train looked fine, but a compression check reviled #5 was only at 30psi. After the motor was pulled and the heads removed, looks like the exhaust valve seat dropped out on #5 and damaged the piston and head. Bores are fine luckily but will at least need one piston and the head repaired. Heads are later casting aluminum M&A's that were fully rebuild at the same time as the motor 7000 miles ago. Never any knock, motor has not seen over 20psi. Just a random event or has this happed to anyone else before?

 

[earlbrown]

Thermal expansion of aluminum is twice that of iron. As a head heats up the amount of press fit can go down.

With any luck a head shop can put in a slightly oversize seat with the correct amount of press.

I'd recommend replacing all the seats just in case the one you dropped was the first one, not the only one.

 

[Undercover87T]

Car came home this past weekend. Two new pistons and both heads were fully gone through, seats replaced and one valve replaced. Got two nice souvenirs.........

 

[cork]

Good to see it back together. Still time for you to make some shows this year.