20832 vs 20831 pistons.
Turbo Mini Forums

From what I've read on the forum after a lot of searching they both seem to be solid skirt but 20832 "early" MG Metro N/A and 20831 the turbo version and the only difference I see noted is the size of the dish (turbo slightly larger).

What about the rings ???

I've previously read the turbo ones are a different thickness to standard pistons but does that apply to both the 20831 and 20832 ???

Reason for asking is I've just acquired a 1275 Aplus on eBay, mostly dismantled (although gearbox complete) and mostly a rusty mess (I could see that from the photos when I bid for it, but it was local and anything 1275 is hen's teeth nowadays) and after cleaning the pile of bits up, it looks like it might be an early MG Metro lump.

Cam is definitely MG Metro (single groove marking), head has the large inlet valves and the pistons are 20832, standard size, and no wear ridge in the bores.

I only really bought it for the block and crank (again standard size but will need a regrind because of the rust) and will offset bore the block to 73mm (it's an un-linered one so I have a good chance of success) but I'm just interested in the pistons, or specifically the rings.

Also, the crank ? Where should the cast/forging number be ? I don't have a standard one out of an engine to compare at the moment but I can't see any markings on this one and it looks like a rolled radius (which I thought was only the turbo crank).

Schrödinger's cat - so which one am I ???

The turbo crank is CAM6581 and is used to be easily identifiable as not being as worn out as they were superior (in metallurgical ways we never really ever figured out - lol) to the factory crank.
I believe they were machines exactly the same as the standard A+ crank...

I was told it's only the 500 odd metro challenge cars that had the special crank the rest where just standard a plus cranks

The 6581 cranks seem to have been limited to early Metros. Both the ones I have coming from C reg models. I never found one from any later engines.
They are certainly better wearing, whether that's a hardening process or a better material, as Dave says, we've never found out.

Phil.

WWW.TURBO-MINI.COM

Thanks all,

After a bit of vigorous wire brushing I finally found the crank cast/forge number or at least enough of it to think it's a CAM6232.

So nothing special but at least has the rolled radius fillets which is what I first saw (all my previous cranks have been the basic 12G1505 so I've never seen the rolled radius before).

It's the pistons I'm really interested in..... are the rings on a 20832 worth anything for anyone who wants a standard size if they fit the 20831.

Otherwise I'm just going to bin them as I'll be reboring to 73mm anyway.

Schrödinger's cat - so which one am I ???

Iirc Isn't the difference in the oil control ring ?

Phil.

WWW.TURBO-MINI.COM

6232 is indeed the stock A+ crank.
I'm starting to think the factory was a little vague when putting the cranks in all these engines TBH. I had an F-reg that you could tell was basically factory fresh; probably never even had a clutch, no signs anyone has ever been in there, and that had the 6581, but I've heard of other stories like Phils on the first and last years being "spotty" as having the fabled crank.



Edited - pretty sure it was F-reg, regardless, was one of the very last...

Edited by TurboDave16V on 26th Feb, 2017.

The turbo and non turbo rings are indeed different; I thought the turbo ones were thicker. It's been so long since I've seen one, I just don't remember...

the one in my car came from a f reg too dave .

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

Early blocks had the groove/groove main bearings (excluding the turbo) and full skirt pistons.

The later blocks have 'WFM1024' in raised letters right under the deck of the block (cylinder 3/4 end) and all the ones i have seen have the groove/plain bearings, the early ones don't.

I'm sure the rings are the same, the pistons differ only by the cc in the dish and the compression height. For some reason AR decided the MG would have a 6cc piston but run the piston down the bore a little, where as the turbo piston had 12cc dish and was nearly flush with the deck. Both pistons look identical in all other respects.

That block I had sectioned, which Turbo Phil is probably using as a door stop, was one of those early MG blocks with groove/groove main bearings. It had spun a bearing (why i decided to cut it up) and all the rings came out in pieces. It had the CAM6232 crank and the part number was also difficult to make out. It looked like it had been sat at the bottom of a pond. I may still have the rods and pistons somewhere.

Interesting stuff,

Schrödinger's cat - so which one am I ???