Dynamo pulley diameters for an S

[Andrew1967]

The Cooper S apparently uses a larger diameter dynamo pulley (3 5/8" as opposed to 3 1/8").

However, the AKD3509 parts manual I have shows ALL models having the 1H998 pulley. Can anyone confirm the diameter of that pulley please, preferably a NOS one with a part number label still attached ?

It seems that part numbers are now 12A1772 and 12G2102 but these seem to be the smaller 3 1/8" (79mm) pulleys, the latter being a one piece steel version and referred to as being fitted to the S ?!

I have a couple of the larger pulleys, one of which came with a 66 S engine, so I'm not saying they didn't have them, just that I cannot find any reference to them. I can see that they may have been fitted to reduce the speed the dynamo turns at higher revs, much the same as the larger pump pulley.

Any pointers in the right direction greatly appreciated.

[Ronnie]

ST did a larger pully C-AEA 535

[Andrew1967]

According to the ST section of the parts manual '535 is a water pump pulley, although a copy of the ST sheet shows it listed under 'Dynamo, pulley, and fan,' but they way its written could refer to the fan pulley

Obviously mistakes and inaccuracies abound, so I'm not saying that what is here is correct

[Ronnie]

Don't forget Andrew the large pully on your dynamo reduces charging efficiency, at low revs, intended for screaming up the climbs or on the tracks.

[Nick W]

Works cars used the 535 cast pulley from what I've read.

[Andrew1967]

Just had a photo of the c-AEA 535 pulley and it is indeed a dynamo pulley, so that’s another incorrect entry in AKD3509 then.

That pulley is huge at about 4 1/8” diameter.

If 1H998 is the same as 12G2102 then either AKD is wrong or all Cooper and S’s had the larger 3 5/8” pulley, as AKD quotes that number for all of them. Minispares state ‘2102 as being 3.1”, which could then be wrong as well, adding to the confusion (mine anyway ).

Here’s a pic of the ST cast pulley and the standard 3 1/8” diameter pulley ! Many thanks to Toby for the photo.

[360gts]

Guess I should throw my 02 cents in.
I have no less than three S's with the 3 5/8" pulleys....two are as original as you can get....the third is currently undergoing restoration right now and it has the correct dated dynamo with the larger pulley.
The 3 5/8 pulley appears to be 12G2102 and was used on other cars...MG's etc.
It was superseded to 12H2102A....these pulleys are not only larger than the standard pulley....they have a stronger center.
Here is a picture showing the 3 5/8 on the left and the standard mini pulley on the right. You can see the center is much better design than the standard pulley.
Also, the larger pulley has a wider lip....by .050"...picture attached

[aga2]

Alittle heath robinson but here is a couple of snaps which also confirms 360gts, mine also 3 5/8" o/d with all correct dated present related items..

Hopefully this also helps Andrew

[Andrew1967]

Nice one Ashley

Thanks to everyone who has posted and PM'd me.