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Identify Engine Block And Head For A 1971 Mk3 Cooper S

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#1 avm


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Posted 10 June 2018 - 11:03 AM



I'm restoring a MK3 cooper S and have a bunch of engine bits I'm trying to identify.. I'm hoping some people on the forum can give me a hand.


I have two engine blocks - a AEG312 and an AEG312 & AEG634. I can't seem to find any information on the difference between these two.. they both seem to be correct for the S as far as I can tell.


I have 3 cylinder heads. An AEG163, 12G940 30A and a 12G940 25D. My research suggests the 12G940's are both for the 1275GT engine so not relevant and the AEG 163 is the correct cylinder head. 


Basically I want to know if I can use either engine block and whether the AEG 163 is a correct fit for this!

#2 InnoCooperExport


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Posted 10 June 2018 - 12:18 PM

I thought the mk3 s head was 12G1805. It's a 12G940 casting with a flat area around the thermostat housing where it should be stamped 12G1805.

#3 pdaykin


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Posted 10 June 2018 - 01:04 PM

I think it should be a thick flange 312 block. As for the head, I think the 163 had been phased out by the introduction of the mk3 and the slightly smaller valves/940 casting introduced.

However, some of the early mk3 'S I've seen have had green engines. Assuming they were original that may indicate that the earlier mk2 block/head combination may have been used.

#4 carbon


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Posted 10 June 2018 - 07:21 PM

The Mk3 S used the thick flange block and the 12G1805 head. The crank should be AEG623 with AEG521 rods.

#5 Moke Spider

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Posted 10 June 2018 - 07:50 PM

Information I have suggests the blocks were the AEG634 casting and an EN16 Tuftrided Crank with 1-5/8" Big Ends.


The head was indeed as per Inno's post;-


I thought the mk3 s head was 12G1805. It's a 12G940 casting with a flat area around the thermostat housing where it should be stamped 12G1805.


These also were drilled for the 10th Stud and the Bolt near the Thermostat Housing and were fitted with 1.4" Inlet Valves and 1.15 Exhausts. To off set the smaller Exhaust, they used a different Cam (AEG510 and later the AEG542) that had 100 added duration to the Exhaust Timing. There was also a different distributor used, with a very minor change to the curve for this combination. With the later change to the AEG542 Cam, they also went over to a 4 bolt Spider Drive Oil Pump and this would probably be the biggest indicator of a block being from a MKIII.

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