Piston Sizes

[Fleetwood Meadow]

I’m thinking about rebuilding my 331 V8 in my Cadillac. It says the standard bore limits are 3.8125-3.8145”. I measured my bores and they were 3.827 across the board. In Engine 101, what size pistons and rings would I need? I’m learning about ring and bearing sizes in this thread. 

[Guest]

Did you check for taper.  Where in the cylinder did you measure.  Obviously you are .013" oversize (3.827 minus 3.814 is .013).  To do the job correctly you should bore the engine .020 OS at least and get new pistons and rings.  Don't forget to align the rods.  While it is apart plastiguage the rods and mains and check the crank for flat spots.  Or you can just comprimise and put .010" OS rings on your old pistons and hope for the best ad many "shade tree mechanics" did/do.  A" trailer queen" might not care but if you were going to drive the car it deserves to be repaired correctly.

One old saying that is still around "Pay me now or Pay me later"

[Rusty_OToole]

From your description the engine has been bored .0145 oversize ( 3.827 - 3.125 = .0145). I doubt they make .0145 oversize rings so you will have to use .020 and file them to fit. To do this you need to put the ring in the top of the bore, square it with a piston, measure ring gap and file as necessary. Clamp a fine file in a vise and bring the ring to the file.

This assumes pistons and bores are good, or at least not worn over .007 taper.

 

I started typing this before Tinindian chipped in.