Quick question about V12 pistons & liners

  1. the Jaguar workshop manual states the liners are stamped A or B on top. I can’t see that on ones from an HE engine I’ve just dismantled. The A is clearly stamped on the pistons

  2. Should the pistons be wider at bottom than top? Measuring, with vernier caliper, below the rings I get approx 3.54". Measuring above the rings I get 3.525"

Yes I believe that is correct as the piston crown is closer to the heat source and so expands more.

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They’re not round, either, they are oval.

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Good stuff as I thought my vernier was playing tricks on me :face_with_monocle:

Interestingly the factory manual and the Haynes don’t give any data for the piston, other than clearance to bore

That’s because you can’t do anything much with the answer. They are what they are and the stuff you CAN measure is what classes them as wornout/scrap. Ring grooves, skirt clearance, etc.