Piston size
 

I have picked up a spare motor the piston is stamped Q4Q, do you think that is 40" over?

Re: Piston size
 

It may or may not be.

I know Hudsons in the 30s and 40s and other cars throughout the years had markings on the top of the pistons. Most of the times it is a manufacturing item, like a letter corresponds to piston size. I have only seen a single letter used, but I have not torn too many engines apart. If you could find out the manufacturer of the pistons, they could probably help you in some way. Btw, I checked google and could not find anything for a code like that.

Re: Piston size
 

It could also be 040, which would indicate .040" oversize. Plenty of engines I've pulled apart have had piston sizes stamped in the top. STD, 020, 040, 060 etc.

Re: Piston size
 

I agree with Dave in Australia's comment.

Re: Piston size
 

Measure the cylinder,s diameter about one inch below the deck. 3.875" + 0.040" = 3.92" is a ballpark estimate of the cylinder's diameter for an 0.040" oversize.

Re: Piston size
 

Someone had lost their "0" stamp and substituted the nearest thing "Q"

Joe B

Re: Piston size
 

The bore measures about 3.913 so that must be 40 over

Piston size
 

Or, maybe eyesight was so bad the installer could not tell the difference between “O” and “Q”?


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Re: Piston size
 

Standard bore is 3.875 plus .040 is 3.915