My motor is sleeved, so that doesn't cure the problem - it may have helped, but it's not good enough.

I'm going to be experimenting with different head gaskets - it's just such a pain in the **** to change the gasket!

 

What size did you bore your new sleeves out to?? Bigger than stock? Another option might be to go to the thicker sleeve with a smaller piston bore size.

 

Performance Motorsports uses oversize ARP head studs, which, IIRC are 9/16 in diameter. Certainly doable, but still doesnt answer the question if the ARP hardware is backing out.

 

May have to go to a locking type of stud/nut to keep things from backing out.

 

The nut isnt physically backing out. But with repeated heat cycling, there is a possibility of some stretch, and a decrease in preload. In this case, a locking nut/washer wont help.

Ideally, ARP recommends retrqing the heads, but we all know that's not feasible, because the cams have to removed to access the nuts.

 

.20 over bore - nothing big and this isn't the problem... this has occurred to every car, liners, sleeves, stock.

The latest theory is the block and heads, although are both aluminum, may be different types and their heating/cooling properties maybe different… A thicker head gasket would probably help if this is the true.