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MG MGB Technical - Alternator Pulley Size

Which is the preferred size for an alternator pulley for a chrome bumper engine?

Thanks

Colin
Colin Parkinson

I don't know about 'preferred', the min Parts Catalogue only specifies one for 18GD onwards 37H8023, the supplement for 77 on for 18ACR alts specifies 13H9514. Suppliers quote 12G1054 and BAU1461 respectively, with some saying the former is 2.75" but quoting an alternative of AEU1238 at 2.5"

I don't know how they measure them but mine on the roadster measures 2.44" OD i.e. across the flange. The alt itself is off a later BL model, so the pulley may have been designed for that. I have a spare alt that came off a Metro and the pulley on that measures 2.7 OD, and tested on the car that gives lower output.
paulh4

FWIW my (original as far as I know) is 73mm - 2 7/8"
overall diameter
Michael Beswick

On further thought the flanges could be anywhere from slightly below the face of the belt to several mm above it and not have any effect on output. The belt on roadster sits noticeably below the flanges, whereas on the Metro alt with a new pare belt wrapped round it is slightly above. Belt tension and age i.e. stretching will have some effect, but MGB belts are supposed to have 1/2" free play in the longest run.

If you are looking for more output, then use the smaller pulley, which was used with the electric cooling fan.
paulh4

Also, consider the use the car will be getting. If racing, use a larger pulley to reduce alternator revs.
Dave O'Neill 2

Dave, no this one is just a road car.

Colin
Colin Parkinson

Swapping Lucas catalogue info with Nigel (sad I know ...) one with Alternator and dynamo info covers pulleys and shows the major dimension is simply the diameter as in the attached.

paulh4

This thread was discussed between 13/08/2019 and 15/08/2019

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