AEG312/AEG634 1275 S BLOCK Of what?

[austinco67]

I want to know what engine it is. Please tell us.

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We know from this forum that it is the late 1275S block. What I just don't understand is the bulge between the core plugs at the front of the block.

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It was mounted on a Broadspeed GT. Please advise.

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[iain1967s]

26 October 1972 thick flange 1275 block
As used on Mini Cooper S Mk3

[austinco67]

iain1967s Thanks for writing.
I understand it is a block from the MK3 era. But that's not what I want to know.

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Areas marked in red. It's about this bulge.

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It's a JAN4 owned by a friend of mine.

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The JAN4 engine block also uses a block with a bulge between the core plugs.

[austinco67]

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And I saw the same bulging block on a COOPER CAR works Mini I saw at the 1999 MINI 40TH at Silverstone. Could it be some kind of special engine?

[BAD942B]

the bulge is also on the new old stock S block that i've got

[austinco67]

Chris, thanks for writing. I have known about the bulging block for 25 years now and have been researching this block, but still no answer, what do you think it is?
Yuji

[360gts]

I just checked all of my thick flange engines.
3 x 1275 These do have that bump you refer to. Latest one is A18M4 18th Dec 74

However, 3 x 1071's do not. Yes, BLM did supply 1071 engines in the 70's with the thick flange.
Attaching a picture of the 1071 block...all three have have same build code.

[mk1]

Hi austinco67, And welcome to the forum!

Thank you for sharing these wonderful pictures of some very special cars.

Sadly, I didn't know about these "bump blocks" until today. I will now have to go & see what mine are like. I will report back soon.

I have also asked a good friend of mine to have a look at the post to see if he can add any more information.

[austinco67]

Thanks for writing 360GT, I didn't realise that thick flange blocks existed on the 1071! Thanks for the valuable photo, I see the S block still existed after production of the MK3COOPER S ended. Were they fitted to any cars other than the Mini?

[austinco67]

Thanks to Mark for willingly accepting a gentile like me.I have been a mechanic for many years. I have been reading this forum for a long time.
I have been looking into bulging blocks between core plugs for over 20 years now. I always thought it was a special competition-only block. I am glad I had the courage to start this topic.
Best regards.
Yuji.

[austinco67]

You can see a video of the Janspeed on You Tube. The same block is used in the restored MK3COOPER S. Very interesting!
https://www.youtube.com/watch?v=XEaRMR-RZPo

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[mk1]

I think that Yuji may have hit on quite an interesting subject here.

For a long time, I have been aware of people referring to a "Special Competition Block" in a number of articles written about works & works supported cars, these references usually date from 1968-ish on. I have always assumed that the block they are referring to is the closed back GT type block, but now I am wondering if they are in fact talking about this "Bulged" block.

If anyone could shed any light on this it would be much appreciated. Also, if you own any 1275 S blocks marked up a 312's could you have a look & see if you do or don't have this particular variation.

The fact that this is seen on cars like JAN 4 & the Broadspeed GT, would suggest that people who "knew" were using this block back in the 1960's. I assume that there MUST be a reason for this.

M

[360gts]

I think that Yuji may have hit on quite an interesting subject here.

For a long time, I have been aware of people referring to a "Special Competition Block" in a number of articles written about works & works supported cars, these references usually date from 1968-ish on. I have always assumed that the block they are referring to is the closed back GT type block, but now I am wondering if they are in fact talking about this "Bulged" block.

If anyone could shed any light on this it would be much appreciated. Also, if you own any 1275 S blocks marked up a 312's could you have a look & see if you do or don't have this particular variation.


Mark, adding a bit more information on this subject.
As I posted earlier...my 3 1071 thick flange engines built in 71 do not have the 'bulge'

I dug out two more thick flange 1275 blocks this morning....built A 9F9 (June 69) and M19E9 (May69)
Now these blocks are different....first, they don't have the 634 casting on the back....just AEG312 and, they don't have the 'bulge'


So, it looks like this bulge may not have shown up till late 71 or 72.......at least that is what I can see from the engines I have.

We need some more information on 71/72 blocks to be sure.

[austinco67]

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The block I posted is A26K2, which means 26 October 1972? Is it?
I am very happy that you all have written. I am very excited because I may be able to solve what has been a mystery to me!

[BAD942B]

I'll have a look with a camera to see if its an extra cooling passage or something when I have a chance

[360gts]

Here is another block I dug up in my storage shop.
This is a June 69 built block
No 'bulge'...and as with the other pre 72 blocks I have....just has the AEG 312 PN cast on the rear.

[austinco67]

Postscript.
The engine is currently being overhauled. I will write about what I have noticed.

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The crankshaft currently set up is MK3 12G1505 AEG623. I thought this AEG634 block was for the AEG623 MK3 crankshaft, but it seems not.

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It has a set of thrust metal for 12H crankshaft conversion and appears to be an AEG480 (EN40B) block. (BLMC) It does not seem to be a dedicated MK3 block.

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（12G1505）　AEG623

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AEG480
I hope this will be helpful.

Yuji

[65MK1S]

Here is the block that came with my 65 Austin Cooper S. The fellow I purchased
it from said that he had a catastrophic engine failure and purchased this as the
replacement. It was a gold seal engine. When I took it apart to check it out and
make sure all was well found out there was zero wear on the engine. I ended up
boring it 20 thou but really wouldn't have needed to if I could have found some
stock pistons. Mains and rods were std. Engine block was AEG312-AEG634 born on
date was A27K2 the day after yours. Engine number pic is included

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