I recently moved, and the 340 (still not in the car) appears to have kicked out one of the brass freeze plugs. Everything was fine while it was running during the break in period, so what would be the culprit? What can I do to get it to stay in the block?

Thanks!

I bought a Pioneer brand freeze plug set on a 340 I am doing, having had success with them years ago. Somewhere along the line they shortened the wall height on them to save a whole penny on the set. They don't have enough support and want to cock in the bore. Garbage.
I chucked them and went with Sealed Power which has the taller original wall heights. They sit square in the bore and are tight.
Also a member here gave good advice to install them by driving them in against the top of the wall edge and not insert/drive a socket against the bottom of the cup.

yes get the thick ones & I prefer permatex #1 gasket cement & put some cement on the block hole ID & the freeze plug

I have always used permatex when installing freeze plugs until i recently had one blow out and found another starting to come out. Removed them all cleaned block well and used red loctite for the install. No more problems.

Bob Mazzolini sells the deep freeze plugs for these blocks (1 5/8" I believe). He has them in stock whereas everywhere has to order them. He sells them for $2.50 each, so not too too bad. That's where I get all mine

I bought these at Summit Racing, so I would have expected them to be of some quality. I will try the red Picture. Thanks!