MGB & GT Forum

Hi All, I have a gold seal replacement engine - 48G733 (1971-72 ish ). Hand-stamped into the engine tag are three additional letters. AD ( under the 733) and K ( at the end of the serial number).

I found this

On Gold seal engines there is a stamped code (not the raised code) on the engine number plate, both letters tell you firstly what the bore size is & secondly the crank size for eg 'A' 'H' is Standard bore with a 40thou crank each letter denotes the size,so first letter is bore size, second letter is crank size
A = STD
B =10THOU
C = 15THOU (crank only)
D = 20THOU
E = 25 THOU (crank only)
F = 30THOU
G = 35THOU (crank only)
H = 40THOU
J = 45THOU (crank only)
K = 50THOU
L = 55THOU (crank only)
M = 60THOU

So AD would mean std bore, crank 20 thou - but what about the K?

I am guessing it could have been rebored again to 50 thou - is that a common size?

The engine also has a large valve head on it.

Any ideas?

Thanks again to all on the forum for your past help.

Paul Arkley

Very interesting. Never knew what the engine code was for my factory re-bulit engine. Still not 100% sure and only the Clausager book references it on page 69 as 'Exchange Engines'.

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Tom C.

Paul,
I am assuming that your Gold Seal Codes came from Barney Gaylord's mgaguru website article titled BMC Gold Seal Engines. However, to complete deciphering the Gold Seal Codes, you also need to read the section titled "GOLD SEAL EXCHANGE ENGINES" at the bottom of BMC, M.G., & Morris Engine Codes where it states, "The code after was to do with rebore/regrind sizes and a job number. " Thus, the K may be part of the job number.

A lot of the information that pertains to the MGA, also pertains the to the MGB, so Gaylords website is a great resource for our Bs.