anyone know anything about piston/cylinder grading

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bmw seem to grade their nicasil cylinders A, B, C, but don't put a matching letter on the pistons

they just have some numbers, presumably referring to size, printed on. does anyone have the info to match the numbers to the letters?

 

[Deleted account 111026]

A 93.96mm
B 93.97mm
C 93.98mm

This is for standard pistons.

 

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A 93.96mm
B 93.97mm
C 93.98mm

This is for standard pistons.

excellent

so any idea what .8 and 8.2 on the piston crown refers to? and more to the point, are they a match for B cylinders?

i would have expected a matching letter on the pistons, but there isn't one, or on the box

IME with other makes, a box contains 1 barrel, 1 piston, rings, wristpin etc. seems bmw do things differently. separately boxed barrels (marked as BMW), and 2 pistons in a box (kolbenshmidt).

 

[Deleted account 111026]

Normally there is a code on the barrels, stamped on the outside, which you then relate to the piston size, ie a barrel stamped with a 'B' uses a 93.97mm piston, (which doesn't have a letter 'B' stamped on it, just it's size).
The 8.2 might refer to the compression ratio of the piston when fitted to it's designated barrel/cylinder head application, but I'm not 100% on this.
If you enter the piston's part number into realOEM (http://www.realoem.com/bmw/select.do?kind=M&arch=1), this will give you it's exact size hence you can determine which grade barrel it should be used with.

 

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Normally there is a code on the barrels, stamped on the outside, which you then relate to the piston size, ie a barrel stamped with a 'B' uses a 93.97mm piston, (which doesn't have a letter 'B' stamped on it, just it's size).
The 8.2 might refer to the compression ratio of the piston when fitted to it's designated barrel/cylinder head application, but I'm not 100% on this.
If you enter the piston's part number into realOEM (http://www.realoem.com/bmw/select.do?kind=M&arch=1), this will give you it's exact size hence you can determine which grade barrel it should be used with.

i should have realised earlier, but the sizes you're quoting are for an R100. these are R80.

i think you're probably right about the compression ratio, and i suspect the .8 refers to the last digit of the piston size, which is given on the piston box: 84.788.

i can't look up the pistons on realoem as they don't have a bmw part number, but i can probably work out the matching from there.

thanks for the help.