TECHNICAL INFO  

 CYLINDER HEADS 

Identification by casting number 

Number Inlet dia. Exhaust dia. Nominal cc Standard fitment 
2A628 1.0625"/26.99 1.00"/25.4 24.5 850, 998 Mini & 948 Sprite 
2A629 1.0625"/26.99 1.00"/25.4 24.5 948, A35 & Morris Minor 
12A1456 1.0625"/26.99 1.00"/25.4 24.5 850, 998 Mini & 948 Sprite 
12G202 1.156"/29.36 1.00"/25.4 26.1 997 Cooper, Austin 1100 Mk 
CAM4180 1.0625"/26.99 1.00"/25.4 25.5 998 Mini - A+ (1980-on) and lead free 
12G206 1.218"/30.93 1.00"/25.4 28.3 Early 998 Cooper, MG1100 
12G295 1.218"/30.93 1.00"/25.4 28.3 998 Cooper, MG1100 
12A185 1.401"/35.6 1.22"/31.0 21.4 First Mk1 Cooper S 
AEG163 1.401"/35.6 1.22"/31.0 21.4 Later Mk1 & Mk2 Cooper S 
12G940* 1.312"/33.33 1.15"/29.2 21.4 1275GT, Austin 1300, all late A+ 
models inc. Turbo but not MG Metro 
12G940 1.401"/35.6 1.15"/29.2 21.4 Stamped '12G1805' on flat area by 
thermostat - MG1300, 1300GT & Mk3 
Cooper S 
12G940* 1.401"/35.6 1.15"/29.2 21.4 As above plus MG Metro 
12G940* 1.312"/33.33 1.15"/29.2 21.4 Single point injection, also numbered 
12G940B cast into head at clutch end 
12G940* 1.312"/33.33 1.15"/29.2 21.4 Multi point injection, also with a number 
starting 'LDF10…' cast into head at 
clutch end and painted black 
 
 
*Note: 
* A+ head castings - despite having the same 12G940 casting number - are considerably different in appearance, loosing the flat area behind the thermostat housing and around the rest of the rocker/head stud areas to a sculptured look - where these areas are replaced by a 'sunken' cast finish. The A+ castings were introduced with the appearance of the Metro in 1980, although some late 1275GTs (1979-on) had them fitted. Generally they are easily recognised by their colour - a putrid yellow on the small-bore castings and bright red on the large-bore ones, a paint finish that is VERY difficult to remove, even in a chemical tank. 
 
* The MG Metro Turbo shares the same valve sizes with the other non-'big valve' 12G940 variants but has 8mm, sodium-filled exhaust valves. 
 
* A+ heads generally have three collet grooves in the valves, collets are 14-degree cone taper instead of the 10-degree on single groove collets (so parts are not interchangeable between single and triple groove types) and the top-caps have a raised ridge around the collet hole. 
 
* SPi (single point injection or 'Tbi' Throttle Body injection) heads are easily recognised by having no heater tap valve port bored through, no by-pass hose adaptor and no tapping for water temperature sender unit just below thermostat housing. 
 
* TPi (twin point injection or 'MPi' Multi Point injection) heads are easily recognised by having no heater tap valve port bored through, no by-pass hose adaptor, no tapping for water temperature sender unit just below thermostat housing and three bolt holes drilled/tapped in a flattened surface immediately below the thermostat housing area to take the alternator bracket. 
Our site uses cookies. For more information, see our cookie policy. ACCEPT COOKIES MANAGE SETTINGS