AEKell@aol.com wrote:
>
> In a message dated 98-08-23 04:43:11 EDT, neil.cairns@virgin.net writes:
>
> << The bores were
> measured, and pistons graded,( by half-thousandths of an inch,) and
> often the grade was stamped on the lower face of the block, ( the sump,
> or pan >>
>
> Neil,
> Could the piston grade also be stamped on the upper face of the block? If so
> (or not), What would the number three mean?
>
> Alan
Yes, it can be stamped on the upper part of the block, but ONLY refers
to the original bore. However, believe it or not, some people actually
stamp the cylinder number by THAT cylinder!!!!!!!!
Looking up the manual for MORRIS/WOLSELEY and MG cars, Morris Engine
Branch would grade the pistons using 1,2,3,4. This number would be
stamped on the PISTON CROWN, and by a cylinder bored out to that size.
The bores were graded the same way, that way you had a piston that
fitted. The system was called 'selective assembly', and was a good way
of using parts that did not quite measure as per the 'blue-print'.
Pistons ASO had their nominal oversize stamped on them, such as +.010"
for a ten thou rebore. Once rebored the figure stamped by that cylinder
means nothing.
Austin used a similar system, but with letters, ie, A,B,C, & D.
The '7', 67 and 60, seen on Greggs blocks base, may also relate to the
size of the crankshaft crankpins fitted. It was not uncommon to get a
poorly machined crank, that was then re-ground to the next undersize,
and you could end up with a STANDARD size set of main bearings, but an
UNDERSIZE set of crankpins, on a NEW engine........but I do not think
this was done on export cars.
If you number '3' was a factory stamp, your ORIGINAL bore size was three
half thousandths of an inch too big, ( .0015" ) so it got a piston to
suit. If it is a factory stamp, it should be inside a diamond shape,
though not always.
Neil.
( with a mind FULL of useless information....)
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