jspeiser wrote:
>
> My B cylinder head is casting number 12H1326 and the casting date is Sept
> 6th, 1966. Go figure.
> John Speiser
>
> ----------
> > From: neil.cairns@virgin.net
> > Subject: Rockers, & Heads, 'B' series.
> >
> > According to details I have:-
> >
> > 1962 to 1970, MGB cylinderheads were casting number 48G318,
Dear John,
I physically have a 12H2708 head, and a tatty 12H4735 in the garage, so
can check them. The number you quote needed more effort. My younger
brother has a 1964 'pull-handle' MGB with a 18GB engine, ( first of the
five main bearings.) I convinced him to take the shiny rocker cover off,
and although the casting number is of poor quality, it looks the same as
yours. ( This number is under the rocker shaft, 2/3rds along the head,
often under lots of black gunge.....)
You are correct! This, being a terrific blow to my ego, sent me off to
source the 48G number...It seems that BMC used the PART NUMBER prefix of
8G for reconditioned components for the 'A' series; 48G for
reconditioned components of the 'B' series; and 68G for the 'C' series.
Infact they used these very numbers as the ENGINE prefix on their
Gold-Seal and Silver Seal exchange engine units. It mattered not what
the engine size was in that series of engines. So 48G318 appears to be a
PART NUMBER of a reconditioned early 1800cc cylinderhead, has anyone got
access to an old parts list? These 8G,48G,68G numbers were not ALWAYS
recon parts either.
It gets more complex when you find out the Landcrab 1800S saloon, ( a
sporting version using the 18H version of the 18V engine,) uses the
12H2708 with a 37cc combustion chamber, giving 9.5:1 comp.ratio.It had a
huge inlet valve as well. This 12H2708 is the 'standard' MGB and Morris
Marina, ( Austin Marina for the US market,) cylinderhead, with the
normal 43.5cc combustion chamber. It seems the 1800S head simply had
more metal machined off the face, and the inlet port opened up a little.
Reminder:-
1962-1970 MGB head, casting number 12H1326
1970-1975 MGB head, .. .. 12H2708
1975 on .. .. .. .. 12H4735 with offset oil feed to
rockers.
Clear as mud!
Neil
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