measured some 2.5 stock .030 over cast Mahles
used a water bath to get the piston temperature evenly distributed
measured at same spot on skirt
at 68F 3.4701"
at 139F 3.4720"
so a 71F difference in temperature
and a 0.0019" difference in diameter
or about 7.7 uin/in/F
2618 forged alloy has a linear expansion ratio of ~12 uin/in/F
Not sure what this cast alloy is supposed to have as far as expansion ratio. Or maybe I am sure since I just measured it lol.
Whats interesting is that the bore measurements I made put the bores between 3.4700" and 3.4750" depending on location.
At this expansion rate the piston would have to get up to 248F to reach 3.475"
Of course the block is also expanding, but less so, so the "seize" temperature is probably much higher than that.
Now it all makes sense...