when my motor blew it cracked 2 pistons and at the same time ( I don't know if one caused the other or what) a valve seat fell out on the exhaust side. why would a valve seat come loose??? Ive never herd of anything like that before. They were ported with 2.02 1.6 valves

 

I've had one come out myself. No idea why.

 

did your heads have bigger valves??

 

Seen a few come out.

My guess is it has something to do with the heat in the head. Seen this most often in heads that have (improperly) been welded on and/or engines that have become too hot. Probably softens the head.

On something catastrophic, like a part letting go.... there's no telling. Could have hit the seat, knocking it out-of-round and there ya go.... the thing comes out.

-Mindgame

 

The most common reasons for dropping a valve seat are in no perticular order.
-Machinist did not setup the press(interferance fit) correctly and they drop when the aluminum expands faster than the iron.
-Head is cracked at the valve seat area and so the aluminum has lost it's hold on the seat.
-Some factory installed powdered metal seats become brittle and shatter after 1000's of miles.

 

I lost a seat on one of my Brodix heads when they were in the car. I think Mindgame is correct. If aluminum heads lose their heat treatment from too much heat, they get soft and bad things happen. In my case, I believe it happened long before I got them, so I was doomed. You can get heads heat treated again. Luckily, mine dropped at idle so it just munched the chamber and the top of one piston. I replaced that piston, put the stock head castings back on (ported), and replaced the rings and bearings.

 

As the L98/LT1 series heads cannot support a 2.02" valve without putting a bigger seat in, I would assume that the press is not correct, they may have put in too much press and deformed the exh seat area so that it dropped out. It would be smart to have the seats TIG'd out and have the press check to make sure it doesn't happen again.