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Re: Piston question

To: "Steve Shoyer" <>, <>
Subject: Re: Piston question
From: "mgamgb" <>
Date: Tue, 26 Nov 2002 22:15:51 +1300
I cant help with the number -

 however the letter stamped on the piston and block indicates the size grade
of the original cylinder bore.  If the letters on the bore and piston match,
and the bore is still standard, then it is a fair bet that the original
pistons are still there.

It is not possible to bore a cylinder exactly to size ( even now days,
although tolerances are a lot tighter) With the B series engines, the
cylinders were bored, they were then measured and marked with a letter to
indicate the departure from the standard bore.

Similarly pistons were measured after final finishing and graded the same

When is came to assembly, all the assembler had to do was to match the
letters.The letters are usually stamped inside a diamond.

I am not sure what the size difference is between grades on a B series
engine, but on a EPAG engine as fitted to a (real) TF, the size grades were
std , +0.0005", +0.001", and +0.0015"

Ian F

----- Original Message -----
From: "Steve Shoyer" <>
To: <>
Sent: Tuesday, November 26, 2002 4:50 AM
Subject: Piston question

> I finally replaced the head on my 1980 MGB yesterday and noticed some
markings on the tops of the pistons.  There was a "B" stamped in the center
of each piston (as well as on the block), and the number "19491" was stamped
near the "Front" indicator on each piston.  What does this number mean?  I
didn't see anything in the archives.  I'm trying to learn if these are the
original pistons or if any work had been done to the engine before I bought
the car.  Thanks.
> --Steve Shoyer (1980 MGB)

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