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MGA What does this founder mark mean?

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Bob Branson

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1600 engine down to bare block, and after scraping the block surface where the head gasket sits, I find stamped into the machined surface off toward the edge and between each cylinder, a diamond with the numeral three. Is this from the factory, or perhaps from a previous rebuild and a trip to the machine shop? TIA.
 
Brinkerhoff

Brinkerhoff

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Bob, I think its explained in the factory shop manual to match the same marked pistons with the bores . The engine blocks were probably finish honed at one station then measured and marked with these code numbers. Pistons from another station were also finished then measured and marked with codes also on their tops. That way the assembling mechanic would only need to match the same codes ( not remeasure and fit each piston to its bore) making assembly much faster.
 
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Bob Branson

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Thanks, you must be right. The block had been bored .030, and the three by each cylinder was probably an indicator of the oversize of that bore. Duh!
 
billspohn

billspohn

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Brinkerhoff said:
I don't think the 3 inside of a diamond has a thing to do with a re bore to .030 over, just a coincidence.
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Correct. The 3 had to do with the measurement of the bores and which pistons would be the best fit - we are talking less than 0.001" increments here. The assemblers just looked at the mark and chose the best pistons from their stack; the bore measurement had been done and stamped by the guy that finished the cylinders.
 
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