Stuart,
The 'A' and 'B' indicate the grade of the piston, meaning where in the
tolerance range the actual measuement for each piston falls within. 'A'
grade is the smallest diameter (low end of tolerance) for both piston and
cylinder. It does not mean a tighter clearance. The grade represents a
0.0005 inch range, or about 1/10 the thickness of a human hair.
This is critical data as piston to cylinder wall clearance must be within a
range narrower than the total tolerance allowed for either the piston and
cylinder. In other words, the max allowed for one would be a bad fit if the
other were at the lowest allowed size. If a machine shop needed to insert a
cylinder sleeve or replace a piston the grade would let them know exactly
what end of the size range was needed.
Also realize that pistons are not perfectly round. They are slightly larger
at the wrist pin than ninety degrees from it. Pistons are also slightly
smaller at the top than at the bottom (skirt).
This info is found in Bentley, section 12.17.13.
Greg Dito
CD6250L
> I cleaned the carbon off the tops of the pistons this afternoon. Five of
six
> of the pistons have "B" stamped on them. The number one piston has "A"
stamped
> on it.
> Anyone know what these designations mean?
>
> Stuart
> 76 Carmine
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