cannot identify these pistons, Please Help

[Boxchevrolet]

hello, im in the process of getting my 350 rebuilt and i cannot find out if it has been bored out before and i can't find a piston size on the pistons, the only thing they say is on the inner skirt and it is M-567, nothing on the top, any help is greatly appreciated

[Peter S]

Just measure the piston.

[Boxchevrolet]

how so?

[Engineer]

Your machine shop should be able to measure it for you. I've never seen a GM piston that looked like that. It is cast and nothing at all fancy or race.

[roboticjunky]

IMO, it's probably standard bore. Look this piston. http://www.competitionproducts.com/Cast-Aluminum-Pistons-Chev-SB-350-Dished-4VR-4000-Bore-3480-Stroke-5700-Rod/productinfo/P567S/#.VoiSJ1J4JpA

Other ones by this brand would have the overbore number added to the end. (Like bored .30 over would be P56730)

I understand yours has a M instead of a P, but could be an old part number.

[timthescarrd]

You are better off mearsuring the bore of the block than the piston.  A 350 should have a 4.000 inch bore.  Use some calipers to measure straight across the openings.  Bored out would be 4.010 - 4.060

[Boxchevrolet]

i measured the top and bottom of the piston and averaged a 4.034 bore, which leads me to think it has been bored .040 before, so now i reckon ill go .060 over hopefully