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MG MGA - Mystery Head?

I have just acquired a second-hand cylinder head from an 1800cc engine with a view to using it on my 1622cc block. It appears to be a 12H2389 casting, being an undrilled "smog" head, but it has two features that I have not seen or read about before. The first is a large "M" cast opposite the "18". I know about "L" engines but can't find anything about "M". The second feature is stranger: the cast numbers "2389" have been ground away and "1325" has been carefully die-stamped just above them. Clearly this has been done too deliberately to be a clumsy attempt at deception, so I can only assume it was done either at the factory or during a previous (gold seal?) rebuild. The date mark is: 15-B-2. Can anyone throw any light on this? The vendor has no idea because he acquired the head in a job lot of parts.

Malcolm
Malcolm Eades

http://www.flowspeed.com/cylinder-ident.htm


12H-1326:

The next heads used (model years 1965-1968) were casting number 12H-1326, which provided an improvement in casting quality. These heads have 1.5625" inlet valves and 1.343" exhausts and the rocker pedestal oil feed hole is in-line with the bolt holes. The combustion chamber type is "closed" with a depth of roughly .400" and a volume of around 42cc's. These heads do not require exhaust valve cut-outs in the block and provide 8.8:1 compression with the shallow dish pistons used in earlier engines. These heads were fitted with "Type A" valves, spring hardware and dual springs.
12H-2389:

For model years 1969-1971, casting number 12H-2389 was used, this being the first of the "smog heads". The biggest change over from the previous heads being addition of the air injector holes destined to adorn all further renditions to come. These heads were still equipped with 1.5625" inlet valves and 1.343" exhausts. The rocker pedestal oil feed hole is in-line with the bolt holes. The combustion chamber type is "closed" with a depth of roughly .400" and a volume of around 42cc's. These heads do not require exhaust valve cut-outs in the block and provide 8.8:1 compression with the shallow dish pistons used in earlier engines. These heads were fitted with "Type B" valves, spring hardware and dual springs.
dominic clancy

Thanks Dominic. I know the Flowspeed site well.

I was more intrigued to know if anyone could explain the circumstances of the number change. It occurred to me that the factory may have had to fill a gap by using 2389 castings on home market cars without the injector holes but changed the number to indicate this.

Also, I have not seen references to "M", only "L".

Malcolm
Malcolm Eades

Malcolm

I will hazard a guess that the 'M' stands for Marina.

Neil Cairn discusses variations between the MGB engine and its cylinder head with that of the Marina in the following document:

http://www.mgcars.org.uk/mgcc/sf/990303.htm

Steve
Steve Gyles

Thanks Steve. That's a good point. I'll see if Neil can add anything next time our paths cross.

Malcolm
Malcolm Eades

This thread was discussed between 13/11/2010 and 17/11/2010

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This thread is from the archive. The Live MG MGA BBS is active now.