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MG MGB Technical - engine identification

Can any body help me id my 1966 mgb engine
is it either a low copmression or high cpmpression engine an also is it 3 main bearing or 5
The engine no is 18S-GB-U-H-2174
Vin no CHN3/104651
I would like to service my own car , dose anyone know of a web site that gives you a service schedule and most importantly the best order to do it in.

thanks carl
carl suthenwood

There used to be a web page ( of funny MGB engine numbers that might have come from a Marina or Sherpa van, but it vanished some time ago. However the suffix letters usually indicate the engine orientation i.e. 'V' for vertical (on the drawings) i.e. fore and aft or 'H' for horizontal i.e. transverse.

But looking again I think the engine is actually an 18GB-U-H-2174, the extra S is to do with a rebuild, or 'service replacement', or something like that I seem to recall. In which case as an 18GB it will be 5-bearing, the U indicating manual gearbox, centre change, unsynchronised first gear, and the H is high compression. It dates to very early in the period Oct 64 to Apr 65 as the serial numbers at the end of that period had got up to 14625.

The chassis number should be *G*HN3/104651, not 'C', and the serial number dates to sometime between Jun 66 and Nov 66, so later than the engine would appear to be, unless you have missed a digit off the engine number, which seems unlikely as the HC engines for that period would have been in the range 43101 to 63765.

Buy the Haynes MGB Owners Workshop Manual, that covers most things mechanical and some electrical, the Leyland Workshop Manual goes a little deeper. For bodywork buy Lyndsay Porter's 'Guide to Purchase and DIY Restoration of the MGB', republished as 'The mgb restoration Manual'. Web sites are useful but no substitute for those books.
Paul Hunt


TVR Grantura 1800S?

This site has a car with an engine number only a couple of hundred away from yours. Of course, his could be a transplant, but it would make sense...


It does say that the owner has just finished a mechanical rebuild, including... "replace motor and transmission (MGB with all-synchro box"
Dave O'Neill 2

Neil - that engine can't be original to that TVR, which is a 1962 model. The 5 main MGB engine didn't exist back then. That car would have bee delivered with a 1622 MGA engine in it and was later re-engined.

My Grantura Mk 3 a year later still had a 1622 originally (that engine is in the garage but buried so I can't check the serial number. It was an oddball prefix.

Here is the write up I did on my car on that same site, now in the loving hands of a racer in Holland:
Bill Spohn

Clausager mentions the 18S engines as possibly being replacement engines fitted to early US cars whose original engines may have had a fault.

Other instances of 18S engines have been found but nobody knows why this prefix was used.

The engine is a high compression 18GB type - treat it as such.
Chris at Octarine Services

My engine number starts 18SV, but as Chris says its a bit of a mystery.


my MGB engine is 18S GD 2519 WE H2519
I have no idea either and would love to know what it means.
Have just opened up the head and it is 12H2709 AF 2H, mgoc say it is a 18 Valve but it is not.
Anybody have any ideas

Many thanks

Michael Walsh

Ignore the S and that will tell you what it is - i.e. an 18GD We H i.e. five-bearing, manual gearbox, centre change, first gear with synchromesh, no overdrive, high compression, used Nov 67-Oct 68.

It's never been really clear what the S means, some say it is a Service replacement, but how that differs from a Gold Seal I don't know, unless the factory or dealer changed the engine for another *new* one (rather than a rebuilt Gold Seal) and reused the original engine number with the S prefix added. The Birth Certificate from BMIHT might confirm that, but if that number is completely different to what you have you will be none the wiser.

Several sites on Google do concur that 12H2709 *is* an 18V (not an 18 valve) head. 18V was the prefix used in place of 18Gx from August 71 onwards.
Paul Hunt

This thread was discussed between 23/10/2008 and 19/11/2008

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