Somerford Mini Ltd. Ordering Parts Using This Catalogue

External Engine - 1275cc (not Cooper S)
No. Part No. Description Qty. Remarks No. Part No. Description Qty. Remarks
1275cc Engine Identification
The first application of the 1275cc A Series engine in the Mini was in 1964, with the advent of the
1275 Mini Cooper S. This particular engine was however a very different animal to the 1275cc engine
described on this page; for the Cooper S unit, please refer to the ‘External Engine - 970, 1071 and
1275cc (Cooper S)’ section of the Somerford Mini catalogue.
The engine described here made do without the eleven stud cylinder head and many other Cooper S
engine attributes and did not have tappet chest covers on the bulkhead side of the engine block - for
this reason it is often referred to as the ‘solid wall block’ 1275cc engine. Its first and only use in a
Mini for just over ten years was in the 1275 GT model, introduced in 1969 and phased out in 1980.
During this period the engine was subject to a number of modifications, not least of which were the
change from twin or ‘duplex’ to single or ‘simplex’ timing chain in 1974 and the gradual introduction of
‘A Plus’ features at the end of the 1970s.
Although not programmed for fitment in a Mini bodyshell through the 1980s, the 1275cc engine was
destined for considerable use in the Austin Metro; for this reason most A Plus modifications were present
by the time of the 1275 GT’s demise, including the characteristically ribbed (much stronger) cylinder
block with its completely revised distributor mounting.
1275cc Mini Engine Serial Number Prefix Codes (not Cooper S) 1969-80
12H/389 1275 GT manual gearbox engine with remote gearchange, rubber coupling drive shafts and
dynamo (1969-73).
12H/390 1275 GT manual gearbox engine with remote gearchange, rubber coupling drive shafts and
alternator (1969-73).
12H/706 1275 GT manual gearbox engine with rod gearchange, ‘pot’ joint drive shafts and alternator
(1973-80). A Plus cylinder blocks ran from engine number 12H/706/-/026400 onwards .
12H/831 1275 GT manual gearbox engine, as per 12H/706 but Police specification (1974-80).
1275cc Mini A Plus High Compression Ra tio (10:1)
Engine Serial Number Prefix Codes 1990-96
12H/-/F53 Manual gearbox engine for carburetter, with 3.105:1 final drive and oil cooler (1990-91).
12H/-/G01 Manual gearbox engine for carburetter, with 3.105:1 final drive; without oil cooler (1990-91).
12H/-/F77 Manual gearbox engine for SPi, 3.21:1 final drive (1991-93).
12H/-/J02 Manual gearbox engine for SPi, 3.21:1 final drive (1994-96).
12H/-/J66 Manual gearbox engine for SPi, 3.21:1 final drive , 55 amp uprated alternator (1996).
12H/-/J77 Manual gearbox engine for SPi, 3.21:1 final drive , 55 amp alternator, air cond. (Japan, 1995-96).
12H/-/J18 Manual gearbox replacement engine with cylinder head, for SPi (1991-96).
12H/-/J13 Manual gearbox replacement engine without cylinder head, for SPi (1991-96).
For the next ten years the Mini soldiered on without a 1275cc variant and the factory declined to put a
genuine performance Mini in the showroom line up (customers being encouraged to look at the MG
Metro instead), despite the popularity of 998cc Mini limited editions like Flame and Racing with their
obvious Mini Cooper styling cues. Finally in 1990 came the new Mini Cooper, complete with a fullyfledged
A Plus 1275cc engine (borro wed ironically from the MG Metro).
This was however a ver y different (lead-free fuelled, with catalytic converter) po wer unit to that seen in
the 1275 GT ten years earlier,having been emasculated to a degree by emission control regulations .
The process of loading up the engine with more and more regulations-compliant equipment continued
through the 1990s, the major milestones being the phased replacement of the carburetter by single point
injection (SPi) from 1991 and a significant overhaul of the power unit design coinciding with the
introduction of multi point injection (MPi) model in 1997. The 1997 on engine, in both MPi and Japanonly
SPi guises, is immediately recognisable by the lack of a distributor, or any facility to attach one!
Meanwhile, by 1992, 1275cc had become the only engine capacity available in the Mini line up (the
lower-powered 998cc unit could no longer cope with all the extra equipment) and that was the way
things stayed until the end of Mini production in 2000. Amongst other things this meant that to
continue to be able to offer an automatic gearbox option, an automatic type 1275cc engine was
produced for the Mini from 1992.
Other applications of the transverse 1275cc A Series included the BMC 1100/1300, commonly referred to
as the ‘ADO16’ range. Higher performance engines from such models as the MG 1300 and Austin/Morris
1300 GT in the ADO16 range were frequently to be found transplanted into Minis by enthusiasts;
particularly in favour was the 11 stud head engine, which is not the same as a Cooper S unit, by the
way. Several other Leyland and Austin Rover cars also used the 1275cc engine, including the Allegro,
overseas-built Mokes and the Maestro/Montego models (the latter featuring a different transmission which
rendered Mini transplants impossible).
The 1980s Metro’s 1275cc unit proved to be the most popular with Mini owners who desired an easy
performance upgrade, the whole engine/transmission assembly less manifolds fitting comfortably in a Mini
with very few necessar y modifications. For this reason, if you see an engine from another car under the
bonnet of a Mini nowadays, it is most lik ely to be one from an MG Metro or its short-lived predecessor,
the Austin Metro 1.3 S.
Engine serial number prefix codes are impor tant in identifying what you have in your car and
establishing which replacement parts to fit to it. The 1275cc engine number prefixes used on non-
Cooper S Mini engines are listed here for that reason. The engine serial number is stamped on a plate
affixed to the cylinder head mating face or ‘deck’ of the cylinder block, at the front of the engine
towards the right hand side , as you look at the engine in the car.
Note that the last code letter before the serial number itself on pre-A Plus engines always relates to the
compression ratio of the engine: H for high compression, L for low compression. A Plus high or standard
(as ‘low’ was then known) compression engines are by contrast identified by the letter plus two numbers
part of the engine serial number prefix; a full list of these is shown below.
Factory reconditioned engines always lost their serial numbers in favour of an engine number plate
stamped with the appropriate part number for the intended application for each engine. In the absence
of an engine serial number on a factory reconditioned unit, this is the only means of identification - but
beware! Factory reconditioned engines were more often than not built up with whatever suitable
components were to hand; for example , new parts were usually plucked from the engine production line
and were therefore of the latest design. Reused components came from stocks of parts which would do
the same job, but w ere not necessarily the same design, all lumped to gether. In other words, parts used
in the rebuild were frequently incorrect in an historic sense for the engine being rebuilt.
1275cc Mini A Plus Standard Compression Ratio (9.4:1)
Engine Serial Number Prefix Codes 1992-96
Note that while standard compression ratio engines were generally non-Cooper units , some expor t markets
did receive Coopers with standard compression ratio engines. Moreover, some numbers of Coopers with
automatic gearboxes were built for export, too. This explains the 1992 start date for standard
compression ratio SPi manual and automatic engines; these engines only started to be seen in UK (and
most European markets) cars from 1994.
12H/-/G03 Manual gearbox engine for carburetter, with 3.105:1 final drive (1992-93).
12H/-/J04 Manual gearbox engine for carburetter, with 3.105:1 final drive (1993-94).
12H/-/G04 Manual gearbox engine for carburetter, with 2.76:1 final drive (France, 1992-93).
12H/-/J05 Manual gearbox engine for carburetter, with 2.76:1 final drive (France, 1993-94).
12H/-/F75 Manual gearbox engine for SPi, with 3.105:1 final drive (1992-93).
12H/-/J01 Manual gearbox engine for SPi, with 3.21:1 final drive (1994-96).
12H/-/J21 Manual gearbox replacement engine with cylinder head, for carburetter (1992-94).
12H/-/J19 Manual gearbox replacement engine with cylinder head, for SPi (1992-96).
12H/-/J14 Manual gearbox replacement engine without cylinder head, for carburetter or SPi (1992-96).
12H/-/G05 Automatic gearbox engine with carburetter (1992-93).
12H/-/J06 Automatic gearbox engine with carburetter (1993-94).
12H/-/F76 Automatic gearbox engine with SPi (1992-94).
12H/-/J03 Automatic gearbox engine with SPi (1994-96).
12H/-/J92 Automatic gearbox engine with SPi and 2.76:1 final drive ( France , 1994-96).
12H/-/J20 Automatic gearbox replacement engine with cylinder head, for SPi (1992-96).
12H/-/J15 Automatic gearbox replacement engine without cylinder head, for carburetter or SPi (1992-96).
1275cc Mini A Plus High Compression Ra tio (10:1)
Engine Serial Number Prefix Codes 1997-2000
12H/-/K70 Manual gearbox engine for MPi, with 2.76:1 final drive (1997-2000).
12H/-/K71 Manual gearbox engine for SPi, with 3.21:1 final drive and air conditioning (Japan, 1997-1999).
12H/-/L13 Manual gearbox replacement engine with cylinder head, for MPi (1997-2000).
12H/-/L16 Manual gearbox replacement engine with cylinder head, for SPi (Japan, 1997-1999).
12H/-/L21 Manual gearbox replacement engine without cylinder head, for MPi or SPi (1997-2000).
1275cc Mini A Plus Standard Compression Ratio (9.4:1)
Engine Serial Number Prefix Codes 1997-2000
12H/-/K72 Automatic gearbox engine for SPi, with air conditioning (Japan, 1997-1999).
12H/-/L14 Automatic gearbox replacement engine with cylinder head, SPi, air cond. (Japan, 1997-1999).
12H/-/L15 Automatic gearbox replacement engine without cylinder head, SPi, air cond. (Japan,1997-1999).
Leyland/Unipart/Rover Mini 1275cc (not Cooper S)
Reconditioned Engine Part Numbers
8G200 Manual gearbox engine, twin ‘duplex’ timing chain (1969-74).
38G527 Manual gearbox engine , single ‘simplex’ timing chain with tensioner (1974-79).
BHM1220 Manual gearbox engine, single ‘simplex’ timing chain tensioner, A Plus block (1980).
RKM1112 Manual gearbox engine; ‘Silver Seal’ par t number. Specification as 8G200 (1969-74).
RKM1130 Manual gearbox engine; later ‘Silver Seal’ par t number. Replaced RKM1112 (1969-74).
RKM1152 Manual gearbox engine; ‘Silver Seal’ par t number. Spec . as 38G527 or BHM1220 (1974-80).
LBB10399 Manual gearbox engine, A Plus, high compression, carburetter (1990-91).
LBB10476 Manual gearbox engine, A Plus, high compression, SPi (1991-96).
LBB10479 Manual gearbox engine, A Plus, standard compression, carburetter (1992-94).
LBB10477 Manual gearbox engine, A Plus, standard compression, SPi (1992-96).
LBB10480 Automatic gearbox engine, A Plus, standard compression, carburetter (1992-94).
LBB10478 Automatic gearbox engine, A Plus, standard compression, SPi (1992-96).
LBB109070 Manual gearbox engine , A Plus, high compression, MPi (1997-2000).
LBB109080 Manual gearbox engine , A Plus, high compression, SPi (1997-2000).
LBB109090 Automatic gearbox engine, A Plus, standard compression, SPi (1997-1999).
Tel. 01249 721421 Fax. 01249 721316 www.somerford-mini.co.uk
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