Heating does expand both but it also makes the metals more malleable and less prone to stress cracking. I would assume it also, loosens the two up. Have you ever tried to take a bolt out and it would not come out. Hit it with the heat and voila.....comes right out. Same theory. I'm sure the expansion rate between the two dissimilar metals may play a role as well, I'm not a metalergenist lol! Favorite Joe Dirt movie quote: "How does the posi track on a hemi work?......... No one knows, it just does!" I was looking for some 4.8 pistons or even better, l33 rods and pistons so, I wouldn't have to deal with this issue.

 

I've had stock pistons break too pressing them off the rod. Usually cuz I'm just pressing them off the rod to throw them away and not really concerned with what happens too them. Never known anyone to press them off to re use them...

 

If you we going to use them again, they should have heated the rod. Don't forget, the pin floats in the piston, it is pressed in the rod. It should not have damaged the piston at all.

 

^^^This.

 

Got them back today, crappy pic but y'all get the point.

As for the other piston that is supposed to be cracked, can't find it, they didnt mark them.....
At least they didn't charge me for removal lol.

 

Machine shop I use do not like pressing on stock pistons. Ive had them do it before and never had a problem but they always pre-warn me they can break. I wouldnt say its a bad machine shop because of that.

 

I'm not banging on them because it broke, I understand stuff happens. The problem is, they didnt warn me that it was an issue, and they didnt want to recoupe me for what they did also, never owned up to there mistake. Further more after looking at the gouges inside the piston leads me to believe they did something wrong. There is also, another quarter-moon mark on the outside of the ring boss where you can tell, they didnt have it level in the press.