1994 Explorer 3G Alternator Pulley Diameter Question?

[9194 Sportman]

Hello friends,
I have a totally bone stock 1994 Explorer Sport 2WD.
It has the 4.0 liter V6, 5-speed trans, 8.8 Diff with 3.27:1 open diff, A/C, Power Windows, Power Door Locks, Power Front Seats, Cruise, Map Lights & factory Stereo system.
I installed a factory Frame Hitch to tow my utility trailer.

So, The factory original 95-amp 3G alternator finally failed and I want to upgrade to the 130-amp 3G optional alternator.
I acquired an 3G 130-amp alternator and when I compared both alternators side-by-side I noticed a couple differences: FIRSTLY, the 130-amp alternator has a larger diameter round body which I knew it was supposed to be, but, SECONDLY, I noticed that the 130-amp alternator has a larger pulley diameter(???).

To clarify, the 95-amp 3G alternator pulley has 2-3/4" diameter, whereas, the 130-amp 3G alternator has a 2-3/8" diameter pulley.

My question is whether I swap pulleys or leave the pulleys alone? There must be a reason for the smaller diameter pulley on the 130-amp alternator(???)

Can anyone explain why there are different diameter alternator pulley AND, which pulley size should I use with the 130-amp alternator on my 1994 Bone Stock Explorer Sport?

Many thanks in advance - Pete

 

[ChildIdenticant]

if you change the pulley OD, you will change the output. Smaller pulley equals more full turns in relation to engine equals more output. I have not installed a high output alt yet ( will very soon) but in my thinking, the deviation in outside diameter from stock suggest an engineering intent. Is the 130 very near the size and weight of the stock alt? from where was the 130 purchased btw?

 

[Roadrunner777]

I actually bought and used a smaller pulley on a 130W. With either alternator, it generates much lower power at idle than while driving. In fact, if you are using a lot of accessory power, wipers+headlights+blower motor, the alternator cannot keep up at idle and you will begin using power from the battery. I noticed this one day by the fact my turn signal blinker was notably slower in this condition while waiting at a stop light.

For many, this is just normal and no concern. But I am in northern MN and I could very easily find myself in this situation while, for example, waiting out a snow storm or being stuck in a ditch. So, from old history I knew one of the things that made a police car a police car was that the factory installed a smaller pulley for essentially this exact same reason. I followed suit and it worked very well for me.

But, there are three drawbacks to doing this. First you have to find the pulley. I found mine at Summit Racing, though it was 10 years ago and I have no idea of the part number or availability. Second, you have to use a slightly shorter belt because the tensioner cannot make up the difference. Third, I don't remember the exact math but the smaller pulley drives the alternator something like 20% faster. That means 20% faster wear on the alternator bearings. I went through 2 alternators in 10 years as a daily driver vehicle.

I'm guessing you got an alternator that was supposed to be for some service vehicle, a police car or ambulance perhaps. You can swap in the larger pulley, it's not difficult to pull. Or use it as an upgrade of sorts, but you will need a different belt.

 

[Kesp4.0]

Glad that this was posted. I always thought mine was problematic as I rebuilt the OEM 95 amp alternator and it works fine but I did notice that at a long stop, when the headlamps are on and I have the turn signals working they will slow down a bit. It also chirps for a few seconds at startup and requires an RPM boost to get it up to mid/high normal range and then the chirp goes away.

 

[Roadrunner777]

The chirping behavior sounds familiar. As you have figured, it is because the belt is slipping slightly on the alternator pulley because at that moment the alternator is drawing a lot of torque. You can try to address it with a new belt and tensioner, and if the alternator pulley looks polished, you will need to hit it with some sandpaper to give it some grip again. Or just live with it. I have had this in many vehicles and it never really hurt anything.

Now you just rebuilt yours, so it really doesn't apply to you but alternators can make what could be taken as a chirp due to a bad bearing or worn slip ring/brushes. To figure this out, take the belt of the alternator and turn it by hand. You will be able to hear a rough sound indicating bearings or a kind of squeak for the slip ring/brushes.

 

[Kesp4.0]

Thanks so much for that info. I will take another look at it