i ve got an alternater but the wheel on the end where the fan belt goes is missing ! does anybody know whether it matters what size the wheel is and whether any wheel of any alternater will fit. ie - do all alternater wheels have the same size hole in the middle to fit the same size shaft or do they all vary ?

Their holes vary and their outer diams vary.

The outer diameters varies considerably depending on the size of the lower pulley and the rpm range of the engine used. There are a few different inner diameters used although there isn't so much of a range so it's easier to find a pulley with the right I/D than O/D

IIRC most alternators go up to about 14,000rpm

I bought a new alternator the same way, wasn't very happy about it either

Got a new replacement pulley on e-bay

Do you know what it's for? try tying the part numbers into Google as often they lead to sites that sell them and then work back from there.

The size of the pulley is determined by the engines idle speed and the crank pulley diameter as the alternator has to spin about twice the engine idle speed to generate current but must not over speed at the engines max rpm

[Edited on 14/2/11 by Mr Whippy]

Thanks everybody !

I bought a light weight alloy one from burton power because I needed the smaller of the two internal diameter pulleys

I needed to put a double pulley on mine to miss the water pipe so have a single one in the garage...theres a few marks on it from removal but would work ok, PM me and I'll send if you want.

AFAIA the bosch and lucas alts have the same internal diameter as mine is now a mismatched pair but one had a woodruff key slot and the other didn't.

[Edited on 15/2/11 by Craigorypeck]