i am currently working on 351c. i am tearing it apart and replacing parts as required. the block and heads are in pretty good shape. someone has done some work on it before. the pistons are stamped .030, so they are oversized. i measured the cylinder bores, and they are right on 4.030. however there is at least another .020 of clearance between the piston and cylinder wall. i can wiggle the piston around inside the cylinder. i don't understand how this could be. the pistons are stamped .030 and the cylinders are an exact .030 overbore. does this make since to anyone?

 

Which end of the piston and how?

Are you talking about a piston on a rod connected to the crank ...
... or just the top inserted in the bore upside down ...
... or across the skirt ...
... or in line with wrist pin?

 

on the rod connected to the crank. havent entirely disassembled it yet. i havent pulled the pistons and measured them out of the block yet. there is just a ton of play. .030 is stamped on the top of the pistons. pistons should be very slightly under 4.030, right? but it seems like they are standard. just a bit confused about it. the only way it makes since is if they are oversized pistons for a smaller bore size. but all fords 289 and bigger are at least a 4" bore.

 

The top of a piston is smaller than it's diameter across the skirt (the top is directly exposed to the heat of combustion thus expands some more) .... and the skirt is measured perpindicular to the wrist pin.

Not sure where you measured the cylinder diameter but usualy the wear is the greatest down in the bore when measured perpindicular to the crank center line as that's where the skirts of the piston are pressed the hardest during the compression and power strokes.

 

i measured down into the bores about 3" and up at the top, both perpendicular and parallel to the crank.

my next step will be to pull it apart and measure the pistons across the skirt and measure the bores again. might be a day or 2. i'll let you know what i find.

 

A piston from top to bottom is shaped like a wedge so it's going to be somewhat smaller at the top.

 

pulled it apart and measured the skirt at the pin. its right on. just seems to be a lot of play up top. guess i never paid that much attention in the past. cylinders are not tapered beyond the limit, so i plan to just rehone, re-ring and reinstall. thanks for the input.