Inexpensive replacement alternator pulleys for underdrive compensation
 

Putting this in general technical since it can affect all engines.

Been posting on how underdrive pulleys cause charging problems and even GraniteGuy has a problem with his system putting out 12.4 volts at idle with the lights all on -- this is too little.

So, after going round and round and finding replacement pulleys to be RIDICULOUSLY expensive ($50 to $80!!!) I found an inexpensive source of them.

http://www.alternatorparts.com/pulley_size.htm

http://www.alternatorparts.com/PULLEY4.JPG

I got the 1-7/8" (1.875") pulley (far right in pic above) which is smaller than the 3.0 engine stock 56mm (2.25" approx, second from left) pulley and should help compensate. It was part number: D1-CS130-018 and is a 6 groove pulley for our belts.

Total cost: Less than $20 INCLUDING shipping!

Thought I'd put that out there for those of you who want to restore some charging capacity.

I'll let you know how quick these guys are and how it works.

They have some reasonably priced alternators as well:

http://www.alternatorparts.com/Ford_3G.htm

great find! Keep us updated on fitment, etc.

Will do, Wayne, and thanks for your help! :smile:

For what it's worth, bunches of old and new alternators that are round shaft and aren't the "keyed" ("Saginaw" style) shaft type; they use a 0.642" diameter shaft. Edit: See further below -- appears to be that 0.642" number is wrong and the correct value is more like 0.670")

I don't know how all the US auto people managed to make something the same on so many vehicles, but they did which can keep prices down on these items!

Griggs, the measurements they are giving, is that to the mountain peak or to the valley on the pulley? Any idea?

how does that compensate for the charging power loss?

It spins the alternator back up to the speed from before the underdrive pulley. You'll lose some of the HP, but will still have a positive gain once it's all done.

smaller diameter = faster rotation at same belt speed, which means better charging.

Think about it: smaller diameter = smaller circumference. If the belt stays moving at the same speed, but it takes a smaller distance to rotate the pulley once, it will rotate more times per given time or distance that the belt travels.

their prices arent stellar on the alternators, i will soon be offering the same alternators for about $70 less. whenever my store gets to its new server!!! The pulley prices arent half bad either, ill have to talk to my source to see what they can do for me.

John do you know the shaft diameter? Or is it a standard? I wonder if their part number is an industry wide number

if you lose HP whats the point to the underdrive pulley mod then, aesthetics or a 1/2 mile more per gallon.....confoosed?

When you put an underdog crank pulley on, you will gain about 8hp and 11 torque based on the same day dyno runs I made. This HP comes from two areas.

1 is reduced rotational weight. The underdog pulley is significantly lighter than the oem pulley.

2 is from retrieving HP that is used up spinning the accessories (a/c, p/s, water pump, alternator). The hp that was used to spin them at the higher rpm is now free to go out the back of the motor to the tranny and on down the line.

With the underdog pullley, dzk pulley, asp pulley, etc, the alternator will not charge below 850 rpm. If you sit at idle for long times your battery will start draining. Normal driving with normal electronics will cause no adverse effects based on the hundreds of pulleys out there being used today on the 3.0 Ranger. I have 40,000 miles on one of my fleet trucks that tows granite daily. No electronics breakdowns have occured.

I went to the nascar races and slept in my Mariner for an hour with the car running at idle to blow the a/c. This is an example of where you may run into problems. Revving and holding the revs periodically should keep the battery charged.

If you have situations like this or if you have large amperage draws, you can change just the alt pulley to spin just the alt back up to speed. You won't get 8HP and 11 torque, but you will get a gain. You still have less rotational mass from the lighter pulley and you are still gaining the HP from the a/c, water pump, and power steering.

Yes, to paraphrase: "by using a smaller alternator pulley, you lose SOME of the underdrive pulley gain, but not all of it, or probably even MOST of it."

HaHa, that sums it up. I have the 1-7/8" and 2-7/16" pulley coming in along with an underdrive water pump pulley. I am gonna head to the dyno when they are all here and get some firm answers on HP, TQ and voltage with the available combos.

FANTASTIC! I love that kind of data, Wayne.

Well, now I'm not so sure I posted the right shaft diameter. I may have to measure it. I've now seen it as 0.672" and 0.642" in different places...if I get a chance I'll mic' the shaft on my "spare" alternator tonight. The 17mm metric ones come out to 0.669" and I've also seen ones listed as 0.670"!

I know there is a wide variety of "interchange" -- but I'm not sure about the rest.

Here's one for you. What if you don't have underdrive pulleys. Can you use one of these pulleys to make the alternator spin faster at idle anyway? I can see how this could be advantageous whether you have underdrive mods or not.

Yes, in fact the site I linked mainly sells them for that very reason -- to guys like you, police departments, etc.

The only thing I saw that suggested a limit was a document that suggested pulley ratios. Basically the guidelines are:

1) A 3:1 ratio (crank to alternator size) is the "norm" in most systems. The speed ratio is the inverse: that is, if the crank is going 5,000 RPM, the alternator will be doing 15,000 RPM.

2) Automatic transmission vehicles (lowered idle in gear) can benefit from a 3.5:1 ratio.

3) Most alternators have a 20,000 RPM safe maximum RPM, though they may be able to go higher for short times. This suggests that vehicle which will be revved high a lot deserve careful consideration about what ratio to use. Our 6,000 RPM limited Rangers probably shouldn't have more than a 3.5:1 ratio in general -- though it really depends on the alternator and how you drive.

Here's a reference on alternator speed guidelines:

http://www.powermastermotorsports.co...r_pulleys.html

Okay, measured the shaft on the one I took out. My mic' says it's 0.668". That's at the very end, just below the threads (only place I can get to). It appears to have a very slight taper to it, so it's average thickness may be a bit more.

DEFINITELY not the 0.642" I spoke of originally. Seems to match the general 17mm spec and close to the 0.672" one as well. Could be they are really all the same just measured slighly differently.

Sorry, missed this in the discussion. They are measuring to the top of the ridges where the grooves are -- not the rim of the pulley, and not the bottom of the groove.

Something to keep in mind when selecting a pulley ratio: engine designers don't use an exact multiple when choosing a pulley ratio. It is set slightly higher or lower to prevent noise or imbalance in two or more FEAD components from staying in phase. Allowing them turn at the same RPM or an integral multiple could set up an audible drone or allow the vibration to become additive and periodic. In other words, something like 2.8:1 or 3.1:1 might be specified instead of an exact 3.0:1.

Ah, that's interesting. So if we replace these we could inadvertently create such a situation if the ratio ended up something like you described?

Any possible damage from this "resonance" effect do you think? Or just a NVH problem?

Yoda, I mean Bob, how the hell do you know so much....... are you a robot?

No damage as far as I know, just possible NVH. It's not a super critical thing, just a "best practices" rule to keep customer satisfaction up and warranty down. Similar to the way tread block spacing is varied around a tire to prevent the set from all from singing the same tune.

im kinda late on this...but so this is to kind of meet in the middle, with power but still having charging ability?

Yes, varying drive and driven pulleys gives you the ability to choose which accessory drive components you want to slow down, speed up or keep about the same.

As far as the RPM thing goes, I think I have hit 5,000RPM once in 3 years and it was for about 5 seconds and solely for the purpose of not being killed. 4,000 is about as high it regularly goes and that is excellerating from a stop.