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Old 07-02-2020, 07:13 PM   #1
Brendan1959
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Default Piston size

I have picked up a spare motor the piston is stamped Q4Q, do you think that is 40" over?
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Old 07-03-2020, 01:05 AM   #2
chrs1961815
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Default 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.
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Old 07-03-2020, 02:52 AM   #3
dave in australia
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Default 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.
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Old 07-03-2020, 06:50 AM   #4
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Default Re: Piston size

I agree with Dave in Australia's comment.
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Old 07-03-2020, 07:43 AM   #5
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Default 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.
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Old 07-03-2020, 09:28 PM   #6
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Someone had lost their "0" stamp and substituted the nearest thing "Q"

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Old 07-03-2020, 11:41 PM   #7
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Default Re: Piston size

The bore measures about 3.913 so that must be 40 over
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Old 07-04-2020, 06:17 AM   #8
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Default Piston size

Quote:
Originally Posted by JoeCB View Post
Someone had lost their "0" stamp and substituted the nearest thing "Q"

Joe B

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


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Old 07-04-2020, 10:02 PM   #9
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Default Re: Piston size

Standard bore is 3.875 plus .040 is 3.915
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