Cylinder head - 970, 1071 and 1275cc (cooper s)

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Rocker Cover Chrome Nut
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ROCKER SHAFT-STANDARD
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SPRING-VALVE INNER-COOPER S
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PLUG-OIL GALLERY-'85 ON
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PLUG-OIL HOLE-CYLINDER HEAD
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SPRING-VALVE OUTER COOPER S
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DISTANCE PIECE-ROCKER SHAFT
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BOLT-CYLINDER HEAD-COOPER S
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970, 1071 and 1275cc Cooper S Cylinder Head Identification  
Cylinder head details in this section are appropriate for all variants of Cooper S engine, built between 1963 and 1971.  Three cylinder head designs were used,
identifiable by casting numbers 12A185, AEG163 and 12G940.  All three will fit any capacity Cooper S engine and all three are interchangeable as complete 
assemblies.  This does not, however, mean that all components can be easily swapped between them.  
         
All Cooper S cylinder heads are referred to as 'eleven stud' heads because of the attachment method to the cylinder block (actually inaccurate since ten studs and 
a bolt are used); all other Mini cylinder heads are attached with nine studs.  The two extra fixings are clearly visible at either end of the rocker cover, the gasket flange 
of which is notched to accept them.  The only other BMC/Leyland engine to be fitted with an eleven stud cylinder head was that to be found in the high performance 
derivatives of the Austin/Morris 1300 (1300 GT, MG 1300 etc.) and the Italian-built Innocenti Mini Cooper 1300, and indeed the cylinder head fitted was the 1969-71 
Cooper S item.  This does not mean however that the 1300 GT engine is a Cooper S engine, since there are many other differences between them, including the 
engine block itself, but it still makes a very desirable power unit to transplant into a Mini.    
         
The first Cooper S cylinder head, introduced on the 1071cc model in 1963, was marked with the casting number 12A185 and additionally may be identified by
a yellow colour coding.  The valves fitted are distinctly larger than those in the cylinder heads of non-Cooper S Minis - the inlet valve is 1 13/32" (35.6mm) in 
diameter and the exhaust valve is 1 7/32" (31mm) in diameter.  Additionally, the valves are uniquely manufactured in Nimonic 80 (EN214N) steel and use double 
valve springs.      
         
Towards the end of 1963 a new cylinder head casting was introduced, marked with the part number AEG163 and colour coded blue or brown.  The only difference
between the 12A185 and AEG163 castings is a production modification in the internal oil ways in the later casting; it affects neither performance nor reliability of 
the head. The valves, valve springs and rocker gear all continued unchanged from the 12A185 head.  The AEG163 cylinder head was fitted from late 1963 through 
to 1969 and thus saw use on the last 1071cc engines, all 970cc engines and all but the last 15 months or so of 1275cc engine production. 
         
The 12G940 cylinder head casting was officially introduced on the 1275cc Cooper S engine at the beginning of Mini Mk III production, for the 1970 model year.
Alongside the casting number in the centre of the top face of the head, the other identifying mark is the part number 12G1805 stamped by the thermostat housing.
It may well also have been fitted to the last few Cooper S Mk IIs; this is difficult to prove, not least because the factory parts and service department soon
offered the 12G940 head as the only replacement for all Cooper S heads, meaning that a significant number of 1960s cars are now fitted with them.  Using the
eleven stud 12G940 head on the Cooper S saved manufacturing costs through component sharing with other models (the aforementioned Austin/Morris 1300 and
Innocenti).        
         
It also improved Cooper S cylinder head reliability, for a small cost in performance, since smaller exhaust valves in the 12G940 head allowed for more material to 
be left between the inlet and exhaust valves; this area was prone to cracking on the 12A185 and AEG163 heads.  The inlet valve size on the 12G940 is, as 
previously, 1 13/32" (35.6mm) diameter, but the exhaust valve size is reduced by 1/16" to 1 5/32"(29.4mm) diameter.  The valves are made from standard, not 
Nimonic, material and have longer stems to compensate for the higher valve spring seat on the 12G940 casting.  Thus even the inlet valves are not directly 
interchangeable with earlier Cooper S items, though their diameter is the same.    
         
The nine stud fixing 12G940 cylinder heads used on other 1275cc BMC/Leyland/Austin Rover engines are not, of course, capable of being fitted to a Cooper S 
engine without very costly modification - they usually have smaller valves than the eleven stud 12G940 (MG Metro etc. excepted) anyway.
         
At various times during A Series engine production, new and reconditioned cylinder heads from the factory were either in 'assembly' or 'bare' condition.  
Assemblies usually included studs, valves, valve springs and guides (but not rockers, rocker shaft and pedestals) whereas bare heads included valve guides 
and studs or valve guides only.  These states of build were however not hard and fast, so if you are offered a new or reconditioned factory cylinder head on an 
exchange unit scheme you should establish before ordering exactly what you will receive, to guard against the possibility of giving away components on your old 
head that you will still need in future!      
         
Rebuilt or Repaired 970, 1071 and 1275cc Cylinder Heads  
Somerford Mini Ltd. offers a bespoke cylinder head rebuilding and repair service.  In our experience, a large number of customers require some degree of modification
to their cylinder heads and as a result, whether you want a standard head or one that is uprated to any degree, we ask you to contact us to discuss your requirements.
It would be helpful if you could also supply us with the details of your engine: full engine number (if known) and type (capacity, high or low compression, gearbox,
breathing system, etc.), plus any existing modifications.  The more you can provide us with, the better we can help you.  All of our cylinder heads are built to 
run on lead-free fuel, unless you specify otherwise.    
Ill. No. Part No. Description Qty. Rqd. Remarks
1      - CYLINDER HEAD ASS'Y, with valves 1 970, 1071 and 1275cc 1963-69.
    (12A185 or AEG163 casting)    
       - CYLINDER HEAD ASS'Y, with valves 1 1275cc 1969-71.
    (12G940 casting)    
2      - CYLINDER HEAD, bare, with guides and studs only  1 970, 1071 and 1275cc 1963-69.
    (12A185 or AEG163 casting)    
       - CYLINDER HEAD, bare, with guides and studs only  1 1275cc 1969-71.
    (12G940 casting)    
         
Gasket Set      
Ill. No. Part No. Description Qty. Rqd. Remarks
3 GEG103SMC GASKET SET, cylinder head 1  
The cylinder head gasket set, also known as a 'decoke' or 'decarbonising' set, includes the cylinder head gasket, manifold gasket, two thermostat housing 
gaskets (one extra to cater for other 1275cc Mini engines with sandwich plates), HS2, HS4 and HIF carburetter gaskets, rocker cover gasket, plus heater take-off 
gasket.  The rocker cover gasket will require two small notches to be cut in it to allow for the extra Cooper S cylinder head fixings.  Valve stem oil seals are not 
included in the set, leaving customers to choose the type and quantity they need and order them separately.  
         
Cylinder Head Components    
Cylinder Head Fixings      
Ill. No. Part No. Description Qty. Rqd. Remarks
4 GEG300 GASKET, cylinder head, copper 1  
5 CAM150 STUD, cylinder head, long 4  
6 CAM151 STUD, cylinder head, short 6  
7 51K1193 NUT, cylinder head to block 10  
8 PWZ106 WASHER, plain 10  
  GB126B WASHER, plain 9 Alternative heavy duty washer. Withstands up to 80lbf ft torque.
9 AEG248 BOLT, cylinder head 1  
10 PWZ106 WASHER, plain 1  
         
Plugs and Adaptors      
Ill. No. Part No. Description Qty. Rqd. Remarks
11 2K1345 PLUG, oil hole, cylinder head 1 Alternative to 6K808.
  6K808 PLUG, oil hole, cylinder head 1 Alternative to 2K1345.
12 12G2092 PLUG, water hole 3  
13 AEA771 PLUG, water and dowel hole 2  
14 12G3503 PLUG, cleaning hole 3/2 Qty. decreases for 12G940 head.
15A 2A243 ADAPTOR, by-pass hose, short 1  
15B CAM4126 PLUG, bypass adaptor blanking A/R Use if thermostat blanking sleeve is fitted.
15C 3H2963 CLIP, bypass blanking plug A/R  
         
Thermostat Housing and Fixings    
Ill. No. Part No. Description Qty. Rqd. Remarks
16      - HOUSING, thermostat 1  
For details of thermostat housings, please see the 'Cooling - Thermostats and Water Pumps' section in the Cooling and Heating area of the Somerford Mini catalogue.
         
Ill. No. Part No. Description Qty. Rqd. Remarks
17 GTG101 GASKET, thermostat housing, cork 1  
  GUG705558 GASKET, thermostat housing, paper 1  
In theory the two gasket materials are interchangeable, but the cork gasket seems to be preferred by Somerford Mini customers for a simple thermostat housing fitment, whereas the later paper gasket is preferred for a thermostat housing with sandwich plate (not applicable for Cooper S engines).  
         
Ill. No. Part No. Description Qty. Rqd. Remarks
18 CHS2515 STUD, thermostat housing 3  
19 FNZ105 NUT 3  
20 PWZ105 WASHER, plain 3  
         
Heater Valve and Fixings       
Ill. No. Part No. Description Qty. Rqd. Remarks
21      - VALVE, heater 1 See note below.
For details of the heater valves, please see the 'Heating - Heater Hoses, Water Control Valves and Cables' section in the Cooling area of the Somerford Mini catalogue.
         
Ill. No. Part No. Description Qty. Rqd. Remarks
22 2A180 PLATE, blanking heater take-off in cylinder head 1 For models without heater.
23 88G221B GASKET, heater valve 1  
24 53K402 STUD, heater valve 2  
25 FNZ104 NUT 2  
26 LWZ304 WASHER, locking 2  
         
Manifold Fixings      
Ill. No. Part No. Description Qty. Rqd. Remarks
27 GUG704053MG GASKET, manifold, standard 1  
28 53K487 STUD, manifolds 6  
29 12A1211 WASHER, plain, large, clamping manifolds 4  
30 PWZ105 WASHER, plain   2  
31 GHF261 NUT, brass, manifolds to cylinder head 6  
  51K1177 NUT, brass, manifolds to cylinder head, long 6 Alternative; easier to access.
         
Rocker Cover and Fixings      
Ill. No. Part No. Description Qty. Rqd. Remarks
32 AEG172 ROCKER COVER, steel, with breather pipe 1 1963-64 open circuit breathing models.
33 AEG512 ROCKER COVER, steel, without breather pipe 1 1964-71 closed circuit breathing models.
34 CAM6822 ROCKER COVER, alloy, without breather pipe 1 Accessory (also MG Metro) item for closed circuit breathing models.
A range of polished or painted alloy accessory rocker covers is available from Somerford Mini; please contact us for details.  Note that some accessory rocker covers require different fixings from the standard items.
         
Ill. No. Part No. Description Qty. Rqd. Remarks
35      - PLATE, engine name 1 See note below.
       - DECAL, engine name 1 See note below.
       - PLATE, engine patent 1 See note below.
       - DECAL, engine patent 1 See note below.
For details of the large range of plates and decals fixed to rocker covers, please see the 'Chassis Plates and Decals' section in the Interior Body Fittings area of the Somerford Mini catalogue.
         
Ill. No. Part No. Description Qty. Rqd. Remarks
36 12A402 CAP, oil filler, black plastic, without breather 1 1963-64 open circuit breathing models.  
37 13H2296 CAP, oil filler, black plastic, with breather 1 1964-71 closed circuit breathing models.
38 GFE6007 CAP, oil filler, red plastic, with breather  1 For CAM6822 alloy rocker cover.
39 12A403 SEAL, plastic oil filler cap 1 For 12A402 and 13H2296 caps.
40 GEG417 GASKET, rocker cover, original 1 With notches to clear cylinder head fixings.
  GEG401 GASKET, rocker cover, replacement 1 Notch before fitting.
41 CAM6822FK CHROME FIXINGS KIT, rocker cover 1  
Includes chrome nuts, chrome distance pieces, chrome cup washers and rubber bushes.  For alloy rocker covers such as CAM6822. 
         
Ill. No. Part No. Description Qty. Rqd. Remarks
42 2A150 NUT, rocker cover to engine 2 Original zinc finish.
  2A150C NUT, rocker cover to engine 2 Chrome, for steel rocker covers.
  CAM6823 NUT, rocker cover to engine 2 Chrome, longer, for alloy rocker covers.
43 1B2925 DISTANCE PIECE 2 Original zinc finish.
  12G687 DISTANCE PIECE 2 Alternative chrome finish.
44 1A2156 WASHER, cup 2 Original zinc finish.
  12G679 WASHER, cup 2 Alternative chrome finish.
45 12A1358 BUSH, rubber 2  
46 12A1968 LIFTING EYE, engine, temporary fitment 2 Fit to engine only while lifting work is taking place.
         
Rocker Shaft, Rockers and Fixings    
Ill. No. Part No. Description Qty. Rqd. Remarks
47 12G1926 PEDESTAL, rocker shaft, with oil hole 3  
48 12G1927 PEDESTAL, rocker shaft, with tapped hole 1  
49 2A258 SCREW, locating rocker shaft 1  
50 2A515 PLATE, securing screw 1 Original item.
51 2A259 PLATE, securing screw 1 Replacement item.
52 51K885 STUD, long, rocker cover and rocker pedestal 2 Outer pedestals.
53 CHS522 STUD, short, rocker pedestal 2 Inner pedestals.
54 LNZ205 NUT, nyloc, pedestal to cylinder head 4  
55 PWZ105 WASHER, plain 3 Not used on tapped pedestal.
56 PWZ106 WASHER, plain 3 Not used on tapped pedestal.
57 AEG399 ROCKER SHAFT ASS'Y 1 Original item.
58 12A1950 ROCKER SHAFT 1 Replacement item.
59 6K878 END PLUG, plain 1 Included in AEG399 rocker shaft ass'y.
60 2K4608 END PLUG, screwed 1 Included in AEG399 rocker shaft ass'y.
61 12G1221 ROCKER, forged 8 Original item.
62 CAM289 ROCKER, scintered 8 Replacement item.
Only forged rockers were fitted to Cooper S engines when built.  However, after the introduction of the scintered rocker on other A Series engines in 1974, either
forged or scintered rockers were offered as replacement parts.  The forged rocker is acknowledged as the stronger of the two and is of course correct for originality.
However for normal road use it does not matter which type of rocker is used, so long as (i) all eight on the rocker shaft are of the same type; (ii) all eight are either 
the same age from the same engine or are new; and (iii) the tappet adjusting screws and nuts, plus the rocker spacing washers, are correct for the type of rocker.  
Note that the forged rockers have replaceable bushes, whereas scintered rockers do not.    
         
Several designs of high-lift and roller rockers are also available for tuning purposes, along with special valve springs to avoid coil binding, if necessary.  Please contact Somerford Mini for details of these and other engine tuning parts.
         
Ill. No. Part No. Description Qty. Rqd. Remarks
63 2A21 BUSH, rocker 8 Included in forged rocker.
64 5C2436 RIVET, bush to rocker 8 Included in forged rocker.
65 AEG167 SCREW, tappet adjusting 8 Use with forged rocker.
66 NT605061 NUT, locking screw 8 Use with forged rocker.
67 12H3376 SCREW, tappet adjusting 8 Use with scintered rocker.
68 51K1178 NUT, locking screw 8 Use with scintered rocker.
69 6K556 SPRING, rocker spacing 3  
70 AEG168 DISTANCE PIECE, exhaust rocker 6 For forged rockers.
71 2A18 WASHER, double coil, outer ends of shaft 2 For scintered rockers.
The distance piece AEG168 is used to shim forged rockers on their shaft correctly over the exhaust valves.  It is only required on big bore (970, 1071 and 1275cc) 
cylinder heads, where the valves are spaced further apart than is the case on other A Series engines.  The wider scintered rockers do not require these shims, so 
instead revert to the more usual A Series set up of using double coil (or 'Thackery') washers at either end of the rocker shaft.
         
Ill. No. Part No. Description Qty. Rqd. Remarks
72 6K555 WASHER, plain, outer ends of shaft 2  
73 ZPS314 SPLIT PIN, outer ends of shaft 2  
         
Valve Guides and Valve Seat Inserts    
Originally on the 12A185 and AEG163 cylinder heads the valve guides were different for inlet and exhaust valves.  The 12G940 head had a single valve guide
design, and this is now offered for all Cooper S cylinder head applications.  This valve guide, 12G1963, will accept the later 'top hat' type valve stem oil seal 
(ADU4905) if required.      
Ill. No. Part No. Description Qty. Rqd. Remarks
74 12G1963 GUIDE, inlet and exhaust valve 8  
75 12G1089 INSERT, inlet valve seat 4 Not lead free fuel compatible.
76 12G2675 INSERT, exhaust valve seat 4 For 12A185 and AEG163 heads.  Pete - is this lead free?
  TAM2069 INSERT, exhaust valve seat 4 For 12G940 heads; lead free fuel compatible. 
         
Valves and Valve Springs    
As stated in the introduction to this section, the valve stem lengths are particular to the cylinder head castings found on Cooper S models, as are exhaust valve 
diameters.  The age of the car provides no guarantee as to which cylinder head will be present.  Please check your casting number and valve sizes before ordering 
replacements from Somerford Mini.  A range of uprated valves, valve springs and caps to suit most uses are also available from Somerford Mini; please contact us 
for details.        
         
12A185 and AEG163 Cylinder Head Castings     
(originally 1963-69 models)      
Ill. No. Part No. Description Qty. Rqd. Remarks
77 AEG593 VALVE, inlet, 1 13/32" (35.6mm) dia. 4 Nimonic 80 (EN214N) material.
78 AEG594 VALVE, exhaust, 1 7/32" (31mm) dia. 4 Nimonic 80 (EN214N) material.
79 C-AEA525 SPRING SET, valves, outer and inner 1  
80 AEA767 SPRING, valve, outer 8 Included in spring set.
81 12G1137 SPRING, valve, inner 8 Included in spring set.
82 88G459 SPLIT COLLET, pair, valve retaining 8  
83 AEA653 CAP, upper, valve springs, steel 8  
84 AEA403 COLLAR, lower, valve springs 8  
85 AEG327 OIL SEAL, valve stem 8  
         
12G940 Cylinder Head Castings    
(originally 1969-71 models)      
Ill. No. Part No. Description Qty. Rqd. Remarks
86 AEG592 VALVE, inlet, 1 13/32" (35.6mm) dia. 4  
87 12G1322 VALVE, exhaust, 1 5/32" (29.4mm) dia. 4  
  CAM4601 VALVE, exhaust, 1 5/32" (29.4mm) dia. 4 Alternative.
88 C-AEA525 SPRING SET, valves, outer and inner 1  
89 AEA767 SPRING, valve, outer 8 Included in spring set.
90 12G1137 SPRING, valve, inner 8 Included in spring set.
91 88G459 SPLIT COLLET, pair, valve retaining 8  
92 88G617 CAP, upper, valve springs 8 Original item.
  AEA653 CAP, upper, valve springs, steel 8 Uprated alternative.
93 AEA403 COLLAR, lower, valve springs 8  
94 AEG327 OIL SEAL, valve stem 4  
Oil seals were usually fitted on the inlet valve stems only, but they can be fitted on exhaust valves too.  Opinions differ on which is better - the choice is yours. 
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