The Ford Barn

mfarley · 07-02-2018, 03:09 PM

I have a 6V alternator on my 29 Tudor Sedan, and I noticed that the alternator pulley is significantly smaller in diameter than a standard Model A generator. The alternator pulley measured 1-1/2" or 1-3/4" diameter and I believe the Model A generator pulley is something like 3 or 3-1/2".

Seems there is always a little more play in the fan belt than should be, and I'm wondering if this is why. Should I account for this diameter difference in belt length, try to put the larger pulley on the alternator, or run it as-is?

Bob C · 07-02-2018, 03:34 PM

The alternator needs the smaller pulley. Does the alternator his the lower radiator return pipe??

Bob

Gold Digger · 07-02-2018, 03:40 PM

I know the alternator needs a small pulley but I have always had to make a special pulley for all of my alternators. I like a pulley about a half inch larger in diameter so I can make the grove in the center deeper. After about 200 miles the fan belts start running on the bottom of the pulley. Seems the belts are too narrow for the pulleys that come on alternators.

john in illinois · 07-02-2018, 04:33 PM

You usually need a shorter belt when switching to an alternator. I have never had any problem with the smaller pulley. They supply those so that it will charge at a lower rpm.

John

arnhemmer · 07-02-2018, 05:02 PM

I switched from an A belt to a modern castellated belt which can handle the smaller alt. pulley much better. The A belts kept on stretching and finally breaking. I got it from Napa auto, just matched up the diameter. It hasn't stretched since I put it on three years ago and clears everything around it do to the belt being slightly thinner. I know it doesn't look like an A belt but a alternator doesn't look like an A generator either.

Jacksonlll · 07-03-2018, 05:39 AM

Sponsored Links (Register now to hide all advertisements)

Run the belt as loose as possible to reduce the side load on the fan attachment to the pump shaft. It's a tapered fit and will wobble if it is not a perfect fit. The way Henry designed it, the load is offset to the rear of the taper joint. Run loose.

SeaSlugs · 07-03-2018, 12:57 PM

also be aware some alternator pullies are installed backwards throwing the belt alignment off. If you look at an alt pulley from the side (perpendicular to shaft)theres a "fat side" and "narrow" side, fat side goes out towards radiator.

07-02-2018, 03:09 PM	#1
mfarley Member Join Date: Jun 2017 Location: Bismarck, ND Posts: 84	Alternator vs. Generator Pulley I have a 6V alternator on my 29 Tudor Sedan, and I noticed that the alternator pulley is significantly smaller in diameter than a standard Model A generator. The alternator pulley measured 1-1/2" or 1-3/4" diameter and I believe the Model A generator pulley is something like 3 or 3-1/2". Seems there is always a little more play in the fan belt than should be, and I'm wondering if this is why. Should I account for this diameter difference in belt length, try to put the larger pulley on the alternator, or run it as-is?

07-02-2018, 03:34 PM	#2
Bob C Senior Member Join Date: May 2010 Location: So Cal Posts: 8,743	Re: Alternator vs. Generator Pulley The alternator needs the smaller pulley. Does the alternator his the lower radiator return pipe?? Bob

07-02-2018, 03:40 PM	#3
Gold Digger Senior Member Join Date: Nov 2011 Location: Arkansas & Alaska Posts: 643	Re: Alternator vs. Generator Pulley I know the alternator needs a small pulley but I have always had to make a special pulley for all of my alternators. I like a pulley about a half inch larger in diameter so I can make the grove in the center deeper. After about 200 miles the fan belts start running on the bottom of the pulley. Seems the belts are too narrow for the pulleys that come on alternators.

07-02-2018, 04:33 PM	#4
john in illinois Senior Member Join Date: May 2010 Location: Illinois Posts: 2,183	Re: Alternator vs. Generator Pulley You usually need a shorter belt when switching to an alternator. I have never had any problem with the smaller pulley. They supply those so that it will charge at a lower rpm. John

07-02-2018, 05:02 PM	#5
arnhemmer Senior Member Join Date: Jan 2015 Location: San Jose California Posts: 150	Re: Alternator vs. Generator Pulley I switched from an A belt to a modern castellated belt which can handle the smaller alt. pulley much better. The A belts kept on stretching and finally breaking. I got it from Napa auto, just matched up the diameter. It hasn't stretched since I put it on three years ago and clears everything around it do to the belt being slightly thinner. I know it doesn't look like an A belt but a alternator doesn't look like an A generator either.

07-03-2018, 05:39 AM	#6
Jacksonlll Senior Member Join Date: Jul 2012 Location: Michigan-- Member of Oakleaf of MARC Posts: 1,686	Re: Alternator vs. Generator Pulley Sponsored Links (Register now to hide all advertisements) Run the belt as loose as possible to reduce the side load on the fan attachment to the pump shaft. It's a tapered fit and will wobble if it is not a perfect fit. The way Henry designed it, the load is offset to the rear of the taper joint. Run loose.

07-03-2018, 12:57 PM	#7
SeaSlugs Senior Member Join Date: May 2010 Location: Central, IL Posts: 3,968	Re: Alternator vs. Generator Pulley also be aware some alternator pullies are installed backwards throwing the belt alignment off. If you look at an alt pulley from the side (perpendicular to shaft)theres a "fat side" and "narrow" side, fat side goes out towards radiator. __________________ 1929 Model AA - Need long splash aprons!