The design piston diameter is 87.160 mm with a tolerance of -0.000 to +0.050
mm. A Grade 3 means that piston is between 0.020 and 0.030 mm oversize, or
87.180 to 87.190 mm diameter. A Grade 5 is up to 0.050 mm oversize. In
inches, a Grade 5 is up to 0.002" oversize.
If you have a clean block, you can sometimes see similar diamond marks next
to the cylinder bores. The design specs there are a bore of 87.200 mm with
the same tolerances. When the engines were originally built, the pistons
were matched to the bores based on these marks.
Don't confuse this with the "standard" oversize pistons we buy when boring
out an engine. Those normally go in 0.50 mm increments, with 0.50 mm being
0.020" oversize, 1.00 mm being 0.040" oversize and 1.50 mm being 0.060"
oversize. The pistons are usually stamped 050, 100 and 150 on the top.
> -----Original Message-----
> From: owner-datsun-roadsters@autox.team.net
> [mailto:owner-datsun-roadsters@autox.team.net]On Behalf Of Andy Cost
> Sent: Monday, November 10, 2003 10:29 AM
> To: datsun-roadsters@autox.team.net
> Subject: piston grade
>
>
> I have some standard bore pistons that measure 87.20 at the
> skirt. They are stamped on top with a 3 inside a diamond shaped
> box. The manual says it it a grade 3 stamp which is between 20
> and 30. It says something about 1/1000 mm units. The only thing
> I can come up with is that the grade is some kind of weight.
> Please let me know what all this means.
>
> Thanks,
>
> Andy Cost
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