3G Alternator - Anything I should know before installing small pulley? - Ford Bronco Forum
 
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post #1 of 8 (permalink) Old 01-02-2013, 02:11 PM Thread Starter
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3G Alternator - Anything I should know before installing small pulley?

So, I did a 3G alternator conversion a long time ago using the alternator off my 94 Mustang. I am about to begin the restoration/build on the Mustang, so I need to snatch the alternator off the truck and put it back on the Mustang.

I ended up buying another working alternator from the parts yard to install on the truck and I have a smaller pulley to install on it so that I can get a few more amps at idle and the belt just simply fits better with the smaller pulley. I used the stock pulley that came on the Mustang pulley, so this will be my first time attempting to use a smaller pulley.

My intent is to replace the brushes, bearings, regulator, and the part that the brushes contact (the name slips my mind at the second), but my question is do you think the diode (rectifier) is up to the task of handling the load of a smaller pulley?

Would it burn up or would it be ok? I just want to be proactive and replace it now with a heavy duty diode (rectifier) if that's the case, but on the same token, if I don't need to spend the $$$ why bother doing it?

My intent is not to cheap my way out of anything, I'm just trying to be smart about it. If I need to buy it, fine, but if not, that's even better. Does that make any sense?

Thoughts?

1990 F150 - 5.0L
Stock GT40 Heads | .030 Over (Speed Pro H120CP30 Pistons) | T-Moss Ported Lower Truck Intake | Comp Cams XE258HR-14 | Hedman Shorty Headers
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post #2 of 8 (permalink) Old 01-02-2013, 03:00 PM
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The pulley size does not matter to the diodes. The max rpm of the alternator is the thing to watch for. I dont think the smaller pulley will be needed with a 3g anyway and you have more contact area with the larger pulley.
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post #3 of 8 (permalink) Old 01-02-2013, 06:14 PM
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What is the size differance between the stocker and this smaller pully. Also where did you get it? Ive bin wanting a smaller one since i run overdrive pullys. The one that came in the box was the same size. Rjm injection (fireguy) claims the large case 3g's are good to 15,000 rpm. Id take his word on that he knows his stuff. Alt RPM = Engine RPM x Crank Pulley Diameter Alt Pulley Diameter

It's not custom if you bought it from a catalog!
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post #4 of 8 (permalink) Old 01-02-2013, 06:56 PM
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Not only does a smaller pulley expose LESS surface area for the belt to grip (making it more likely to slip, heat up, & wear away); it also forces the belt into a sharper bend, which causes its internal fiberglass cords to age/break faster. Try it with the normal pulley for a few months.

What electrical loads are you running at idle that makes you think you need more current from the alt?
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post #5 of 8 (permalink) Old 01-02-2013, 09:08 PM Thread Starter
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Well, I don't have anything that specifically requires increased amperage outside of of the truck having all power options, but I've never particularly cared for the way the heater fan has been a power hog. When I turn the fan on, it takes the voltmeter gauge moves quite a bit. The heater fan works fine, but it seems to take quite a bit of juice.

1990 F150 - 5.0L
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post #6 of 8 (permalink) Old 01-02-2013, 09:09 PM Thread Starter
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They sell smaller pulleys on eBay. If you type in '3G Pulley' you'll see quite a few results. That's where I got mine from.

1990 F150 - 5.0L
Stock GT40 Heads | .030 Over (Speed Pro H120CP30 Pistons) | T-Moss Ported Lower Truck Intake | Comp Cams XE258HR-14 | Hedman Shorty Headers
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post #7 of 8 (permalink) Old 01-02-2013, 11:02 PM
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Rjm sells three differant size pullys. 2-5/8,2-1/4 and 1-7/8. So from biggest to smallest your loosing 3/4" i dont see that causing any trouble with belt slipping. Ryan also states that belts dont start to slip untill the alt makes 180 amps. Im going to run the 1-7/8 since after some quick research states that it will return my alt back to stock charging amps at idle.

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post #8 of 8 (permalink) Old 01-03-2013, 01:26 AM
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Quote:
Originally Posted by qdeezie View Post
When I turn the fan on, it takes the voltmeter gauge moves quite a bit. The heater fan works fine, but it seems to take quite a bit of juice.
That's not something the alternator can fix, even if you get a 300A version. It actually SUGGESTS a more basic problem with your electrical system. Click these & read the captions:

.

Once those are all good, inspect the blower fuse socket & terminals for signs of heat - they commonly melt & burn without blowing the fuse. Then check the switch terminals on the back of the A/C panel, the resistor terminals under the hood, and the motor connector terminals. Finally, remove the motor, clean the squirrel cage, and lube the motor bushings. While the motor is out, check the evaporator for a buildup of leaves, and remove it for cleaning if necessary.

. . . .

If the evaporator is nasty, the cowl drains are probably worse:

.
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