425 Nailhead

[Grhopperass]

I'm been offered a 425 nailhead that has been rebuilt.
it is bored .040 with cast pistons & chrome moly rings.
I'm told that this is the maximum a 425 can be bored
out and that the 401 ( which I currently have) is a much
better block.
Can anyone out there give me advice here.
I appreciate all the help in the past, I want
to make sure I make the right decision.
Cheers
IF

 

[Dr. Frankenbuick]

They do make a .060" over 425 piston, but that does not mean it can be used in many blocks. Core shift and thickness varied in these engines. So, .030" to .040" over generally leaves enough cylinder wall thickness, but not in all cases. The best way to find out haw far it can be bored is to have the block sonic tested before machining.

The 425 you are thinking of purchasing is probably alright, but that is probably the last overbore it will see. Meaning this will be the last rebuild possible. Was it used in a car, did it have any overheating or other issues? Can it be run for you? I would want to hear and see it run before purchasing an engine that can not be rebuilt again.

HTH :wavey: