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Old 08-23-2014, 09:55 AM   #1
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Overrunning alternator pulley?

Does anyone know the shaft and thread dimensions (length and diameter) for a GTS alternator? Letting the alternator freewheel when it's not driven is very beneficial to belt and tensioner life, it's also a small boost to engine efficiency, and best yet reduces spinning mass on engine deceleration. The alternator rotor and shaft is typically about 90% of the weight of the alternator, so for ours it would be about 8-10 lbs of mass spinning at roughly 3x crank speed due to pulley ratio! That's a lot of energy to slow down each time you want to change gear. I'm a little light on math to figure the moment of inertia and how many lb/ft of stored energy that is,but if you've ever spun an alternator by hand and then stopped it by hand you can feel it's got some serious heft just at 100rpm, now imagine at 20,000 RPM!

I'm trying to figure out if there's a cross from a commonly available pulley to fit our alternator, I'm hoping maybe a later model Camry/Corolla uses the same alternator innards and shaft size so it's just a direct swap over. The pulleys for a 2010 Corolla are about $50. I have no idea if it would make any appreciable difference however EVERY new car is using them so there must be some benefit to offset the cost and enough for the bean counters across the industry.

From the rebuild procedure outlined in Alldata the shaft of a 2010 Corolla alternator looks like it's externally threaded and tapered like a standard alternator shaft. If anyone knows the dimensions of ours I can get the dimensions of the 2010 Corolla or other models from one of my suppliers at work as they'll be likely to have that stock on hand, but unlikely to have on hand the stock for a 10yr old sporty coupe/rare corolla model.
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