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MG Midget and Sprite Technical - Fan Belt Woes

Also posted this on MASC Facebook Group.

Fan belt woes.
My fan belt broke last week. I have tried to fit two recommended replacements. UNIPART GVB 10864, (10mm wide 864mm long), and a QBA 838 from Moss (9.5mm x 838). Both are too short to fit over the wider outer radius of the alternator pulley although I think they would just about fit into the groove if I could get them across. Measuring the broken belt its about 860mm long, a shorter length than UNIPART replacement!
Looking closer I can see that the old belt looks much more narrow than the 9.5 mm and 10mm wide replacements. Photo attached. This would mean it fits deeper into the V in the pulley. Thus fits OK despite being similar length? Appreciate advice or experience of anyone who has had similar issues?
59 Frog, but with 1275 engine and alternator fitted by previous owner in late 90s.
Many thanks.
Steve



Steve 59 Frog

I have loosened the alternator as much as possible on its slider. Last resort is to detach it and reassemble with fan belt in place. However if new ones are too wide this may cause future issues?
Steve 59 Frog

Steve,
do you know if your pulleys and alternator link arm and fixing are standard size?

Are you loosening all four bolts enough to retract the alternator?

On my 1275 with alternator the fan belt is 838 x 10 (the 838 in the inside measurement, 848 outside).

I'd personally advise you to avoid the generic belts often supplied by the likes of Moss and instead go for a good make such as Gates, fit 'n'forget.

You could measure your requirements and see what fits from the catalogue, allow either way for installation and adjustment.

http://www.gatesautocat.com/article/6271MC
Nigel Atkins

Also why did your fan belt break?

Age, you want to change them at say 5-7 years as a service item, if not age then there might be a reason for your problems finding the right size, and for the belt breaking.

Or there might be another explanation.

ETA: I've had previous problems with belt size, resolved on here, and almost losing two belts by showing off.

Nigel Atkins

I always kept a 10900 belt as it was a universal fit on most midgets,MGA and MGB
From memory-which is a bit cloudy nowadays ,the correct belt for a 1275 with alt. is a 9.5 x 863
But then I'm hanging off the bottom of Aust.
lol
willy
William Revit

I use a Quinton-Hazell QBA900 on a 1275 with alternator.


Alan Anstead

Thing is we don't know if the engine is a Spridget engine or from elsewhere, then the alternator may not be standard, or pulley change, hence the bit of string measure and link to the 'Dimensions Search' at the top of the Gates web page.

My 838 is only just long enough to tension the drive with the link arm slot extended.
Nigel Atkins

Willy,
as my Midget is a very early 1973 car it originally would have be an early one from the change from dynamo to alternator and as I subsequently learnt shortly after the alternator pulley size changed so there are two belt lengths for the original set ups, 838 and 863.

But my alternator isn't standard and the fittings to it never seemed right even with the previous alternator that came with the car, that packed up, but that's whole other story ... :)
Nigel Atkins

I think I found a 900mm length Bosch fan belt that was useful on my MkII Sprite with a dynamo (sold for various old VWs and an Alfa IIRC) after having fun with belts supplied by marque specialists. I will check to see if I can find the Bosch and VAG part numbers, so available from a wide range of sources.

The world of generic part numbers for fan belts is fascinating, and seems to often include the length in mm (and something to denote the section shape and width?). I would also be tempted to work out what belt would suit as made and directly supplied by one of the big and quality fan belt belt manufactuers, such as Gates, as suggested previously, and head for an industrial belts supplier.

Cheers
Mike
M Wood

On checking my fan fan belt, it is a 875mm long, 10mm/9.5mm wide -
Bosch part number: 1 987 947 626 (made in the UK - probably new old stock). Quinton Hazel also sell one that is 875mm long: QBA875. If you think you want one slightly shorter than 900mm.

Cheers
Mike
M Wood

Mike
on the Bosch list that belt is indeed 875x10 which would be very close to the 863x9.5 as the 9.5 would sit lower in the v of the pulley

I think i kept a 900x10 as it fitted several other cars as well and was a good emergency belt to have laying around
Sounds like 875-900 x 10 is what Steve needs, but as Nigel notes there are different pulley sizes and mounting brackets out there so not all cars will be the same as this one-and yours

willy
William Revit

This thread was discussed between 11/08/2020 and 13/08/2020

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.