Attempts to diagnose it's ills through the medium of Google unearthed the usual array of half truths & entirely unrelated tosh, except for a couple of items buried deep in forums, one was a guy who'd had his alternator overheat due to insufficient wire capacity, another was a guy who'd cooked the alternator by over-speeding it.
In time honoured fashion, it was time to " 'av the back off it" which revealed the following scene of horror:-
My research had revealed that an 18ACR alternator should spin at 12,000 RPM max. The engine pulley was 130mm dia, the alt pulley was 55mm. So the alt. was spinning about 2 1/2 times as fast as the engine, so at the 7k rpm redline, that's erm - 17,500. In fact the alt was all out of puff at a pedestrian 4,800 engine rpm. I had assumed it to be OK as the pulley is off a Zetec Mondeo, but either they have a much smaller crank pulley, or they're rated to much higher RPM. It looked like the ideal was 73mm dia, & several websites were keen to sell me a bespoke, lovingly crafted piece of aluminium alloy for upwards of £80 - thanks, but no, I like to save lbs, but I also like to save £s. I did find a guy selling something that was almost what I wanted on e-bay for a more reasonable £25, but he didn't respond to my e-mail. So for the princely sum of £12, I purchased a steel "item" from a boatyard, which was the right diameter - but weighed in at a hefty 565g.
The pulley is now a svelte 380g. There was talk in the Cave about balancing & the possibility of using the accelerometer in an iPhone to check for balance, but being a simple soul, I went home & rolled it along the kitchen worktop. When it came to rest I marked the lowest point I rolled it again in the same place, it stopped 1/4 turn out, on the third roll it stopped just over a 1/4 turn the other way, & the forth roll stopped somewhere around 1/2 a turn off (ish), so I think it's a balanced as it needs to be - anyway, alternator bearings are cheap.
So tomorrow I'll pick up the new drive belt & get it all on the car, but this evening finds me woman free, so I sit here eating pizza while typing & drinking red wine from a tumbler - hurrah!! (fear not dear reader I am NOT dressed in only a vest & Y-fronts - I'm not that blokey).
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