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MG Midget and Sprite Technical - Crankshaft part numbers

I have just stripped my spare 9C engine and wonder what crankshaft I have. Difficult to read the number on it but it looks like AEA07 something or other. Or it might be ?AE407. The parts list says it should be 88G225. The factory uprated crank was AEA406 - too much to expect it to be one of those. There is another number adjacent which says ESC4A/4. It's in very good nick and only 10 thou undersize.

Any crank experts out there?

Les
L B Rose

it is very common for bare casting numbers and finished part numbers to be 1 different, so AEA406 and AEA407 makes sense. However I have no direct experience of the small block engines, maybe Dave O knows?
David Smith

No expert but I believe the competition crank which was part number AEA 406 - was marked as 407 on the forging. Like the race 648 cams were marked and called 649. it was the BMC drawing Office numbering system at the time. Commonly called the red crank it was nitride hardened. Does it have a reddish appearance or dull grey? Are there any web drillings to suggest it's been balanced? I think some of the early Sprites had them fitted as standard anyway.
f pollock

The competition crank part numbers for the 950 engine are C-aea-406(red crank), C-aea 461 (nitrided Formula Junior) and C-aea 792 Tuftrided.
Bob Beaumont

Yes it is reddish. Here is what it looks like. No sign of balancing.

Les

L B Rose

I may be wrong but I had a 950 crank which had a reddish tinge but it was a standard one ( it came out of a morris minor) I think the red crank is much more obvious in colour with evidence of balancing.
Bob Beaumont

But it should be marked 88G225. No sign of that anywhere. Were all competition cranks balanced? I gather that the factory was quite haphazard as to what they put together, depending on what was in stock.

I'd be surprised if after 60 years the red stain had not faded a lot!
L B Rose

Correction - there is a chunk machined off the rearmost web, so some evidence of balancing. The overall colour is a bit redder than the photo shows. Vizard's book says the red crank was EN40B. Is there any way of testing that non-destructively?

Les
L B Rose

Les,

The material can be tested non destructively but you'll need to find someone with what is known as a brick on a stick, ie a handheld xray spectrometer. I worked for a number of years in the industry and one of my ex bosses had one in development and the brick on a stick refers to the upper unit being about the size of a brick and the handle being the stick. they contain a portable xray source and detectors and analysis software. Works wells but expensive IIRC makers are Niton and Oxford Analytical, maybe others.
David Billington

This thread was discussed between 24/10/2018 and 26/10/2018

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