Does anyone know what these D's are for?

I have found those on various blocks going back to the 60s. All I can think of, since the factory paint didn't stick well to them, is they are part of the manufacturing process. Like "D" for "this cylinder is DONE being machined, move to the next one" or something.

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Casually looking for a Clifford hyperpak intake for cheap.

Easy. Doug Dutra

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Official Cookie and Mater Tormentor.

D-D-D-D-D-D....Bat Man!!

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-MattMan
LEANED & MEAN

I'm not used to seeing Ds on the outside of the block. On the oil pan rail near each cylinder of the V8s Chrysler stamped a bore size code so that the assembler would choose the correct size piston for correct cylinder wall clearance. D is the largest if memory serves. My best guess on that block is that the sizes were drawn on the block and that paint adhesion suffered as a result.

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Joshua

interesting... I would say that they possibly layed something out on there when it was getting painted and it happend to be in the shape of a D

or maybe it meant something was installed? done as in brackets, plugs bolts were torqued or something.

or it could have been a gf's initial and some guy was day dreaming and writing it the blocks lol

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69 charger with factory Slant 6 3-speed on the column

I was thinking Doug Dutra lol!! But yes it was strange. I have never seen it.

I've removed paint from aluminum 225 blocks to find "A", "B', "C" type marks, one per cylinder. My understanding matches Josh's.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Bore size... as noted above.
Mass production engine assembly line machinists simply bore & hone the blocks into a tolerance range.
Later, an inspector measures and then marks the needed piston size code... somewhere on the block, where the engine assembly workers can see it.
The assembly worker hopefully installs the stated piston size into the marked cylinders.
DD

Mhmm that's interesting. I learn something new everyday. Thanks

Really interesting! Makes sense to use all blocks that can be saved.

How much oversized the "D" sized piston be?

.004?

And would it be because of a manufacturing error or human error that such is being done?