Fan belt size for Mini Cooper S MK2

[minstix]

Hi,

I'm having a bit of a dilemma regarding the correct length of fan belt for my MK2 Cooper S restoration project. I thought it would be a quite straight forward thing to look at the usual mini parts suppliers websites and find out but it's not that easy. Mine is a standard setup with original pulleys, original (refurbished) C40 dynamo. New water pump though but all pulleys are the original ones.

I understand that the part numbers are, for example, GCB10813 etc where the last three digits are the length in mm.

Cooper S cars had a larger diameter dynamo pulley so it doesn't over rev the dynamo. Mine has the original one. It seems to be about 92mm in diameter going from the very furthest edges across (not inside the V where the belt sits).

I can't find anywhere which clearly says which size I should be fitting on a 1969 Cooper S MK2 with dynamo. I can find references to early 998 cars and later 1275 cars with alternator.

Can anyone point me in the right direction?

Thanks for your help as always,

Steve

[floormanager]

I'll check mine in the morning but I believe it's the 813. I know I had a belt on it previously, which was too long.

[Spider]

I'll check mine in the morning but I believe it's the 813. I know I had a belt on it previously, which was too long.

This is it.

[minstix]

I've tried an 813 but I can't get it over the dynamo pulley, no chance when the dynamo is hard against the engine. The next size up is 838.

I wish I'd kept the one I took off a few years ago when sripping the car down. I think I may have just cut it off and chucked it in the bin back then. I had fitted that one years ago and don't remember struggling. Hmm...

Steve

[Spider]

When you refer here to the pulley;-

Cooper S cars had a larger diameter dynamo pulley so it doesn't over rev the dynamo. Mine has the original one. It seems to be about 92mm in diameter going from the very furthest edges across (not inside the V where the belt sits).

Are you meaning it's been fitted with the Special Tuning Pulley C-AEA535 that would normally take the Fan Belt that comes up as Special Tuning C-AEA756 ?

This is a 10A0850 or some may list it as a 850.

[NZmember]

I just had a similar experience. It was caused by a stud holding the alloy spacer for the engine / rad mount. I filed ~1mm off the end of the stud which then allowed the belt to fit through the gap and sit on the bottom pulley. Difficult to see, but luckily I checked before putting the engine in.

[minstix]

I managed to fit through and get it to sit nicely over the bottom crank pulley and the water pump pulley. It then won't go over the dynamo pulley.

Steve

[TECH396]

My 68 S originally came with AEJ101 and a NOS one measures 840mm and is the one for the setup you described, and the one I used on my car with the same setup.

[GraemeC]

If you’re unsure, just set the dynamo in the middle of its adjustment and then use a length of string wrapped around the pulleys to measure what’s needed.

[minstix]

The string idea is so simple, why didn't I think of that. Thanks, I'll try with some thick-ish stuso it doesn't go right to the bottom of the V on the pulleys and let you know the results.

I'm not sure how they measure the diameter of the pulleys, maybe not from the furthest edges as I've done. But it seems that the standard size of dynamo pulley that was fitted to a Cooper S MK2 was 75mm wide, part number 12G2102 and is still available new (for about 80 quid, so I'll avoid buying one unless I have to).

I'll let you know how the string works out.

Steve

Dynamo pulley Cooper S.jpeg

Dynamo pulley with ruler showing diameter of 92mm.jpeg

Dynamo pulley 92mm diameter.jpeg

[Peter Laidler]

Your question was just too ambiguous Minstix. There were just too many variables to cater for. I was going to suggest another way to suit your particular situation........... But Graeme's answer is even simpler than mine!

Where there's a will, there's uusually a simple way - or answer! Thanks Graeme

[minstix]

I've tried Graeme's string idea using thin rope that's about 5mm thick so it doesn't sit right down into the V on the pulleys. With the dynamo mounted and tilted to about the ideal position, which is about half way along adjustment, I pulled the rope reasonably tight and marked it where they met. Then measuring it came out to 340mm.

That's pretty close to the 838 belt that's available, part number GCB10838. That's the next size bigger than the one I originally tried which was the standard GCB10813. The last three digets are the length in mm. So if I order an 838mm belt it should fit. Thanks Graeme for such a simple but affective idea.

Steve

[TECH396]

I've tried Graeme's string idea using thin rope that's about 5mm thick so it doesn't sit right down into the V on the pulleys. With the dynamo mounted and tilted to about the ideal position, which is about half way along adjustment, I pulled the rope reasonably tight and marked it where they met. Then measuring it came out to 340mm.

That's pretty close to the 838 belt that's available, part number GCB10838. That's the next size bigger than the one I originally tried which was the standard GCB10813. The last three digets are the length in mm. So if I order an 838mm belt it should fit. Thanks Graeme for such a simple but affective idea.

Steve

Belts are measured along the length of the outside. You need a 840mm belt as per factory original.

[minstix]

Sorry, it should have read 'measuring came out at 840mm' not 340mm.

Steve

[GraemeC]

I've tried Graeme's string idea using thin rope that's about 5mm thick so it doesn't sit right down into the V on the pulleys. With the dynamo mounted and tilted to about the ideal position, which is about half way along adjustment, I pulled the rope reasonably tight and marked it where they met. Then measuring it came out to 340mm.

That's pretty close to the 838 belt that's available, part number GCB10838. That's the next size bigger than the one I originally tried which was the standard GCB10813. The last three digets are the length in mm. So if I order an 838mm belt it should fit. Thanks Graeme for such a simple but affective idea.

Steve

Belts are measured along the length of the outside. You need a 840mm belt as per factory original.

The AEJ101 you mentioned earlier lists as equivalent to 838mm

[TECH396]

GraemeC
The AEJ101 you mentioned earlier lists as equivalent to 838mm
[/quote]

Sue me