Alternator pulley sizes (OEM underdrive !?) Need your help guys

[carotman]

I have 2 spare alternators for my old A20A engine. One came originaly in my car (A20A1) and the other was swapped during my EFI conversion (came from an A20A3.

I was rebuilding them yesterday and comparing parts with the B20A alternator and noticed that the pulleys are different on the A20A1 and A20A3 alternator.

The A20A1 has a larger pulley than the A20A3. This means that the carb alternator will spin slower than the EFI alternator. Since both alternators aren't the original ones that came on the cars, I don't know what to say. The carb pulley was around 2 to 3 mm larger than the EFI one on the diameter. They have the same width and same number of grooves..

www.torringtonhondaparts.com lists both alternators as being the same except the voltage regulator (the EFI has 4 pins and carb 3). Other than that they are identical. You could even run an EFI alternator on a carb engine if you get the EFI connector and do not connect the 4th wire... They also list 1 single pulley for both alternators.

I need people to measure their pulley sizes to compare the 2 I have here.

I don't know if this has been discussed before and I'm a retard but I just realised this resterday. Lol.

Oh, BTW, the A20A and B20A have the same alternator except for the stator casing and the pulley.

[FyreDaug]

Hmm, I have an A1 and I got an alt from an A3, I didnt notice any diff except the 4pin connector was a bitch, because I didnt know at the time. Had to make another hour trip to get there.

[carotman]

In fact, you could just have swapped the regulators on the alternator and it would have been fine

The pulley diameter isn't that obvious.. I had to stack the 2 pulleys to actually notice.

[FyreDaug]

Yeah but I didnt notice until it was already back in, I didnt drop the axle to get at the alt, so by the time it was forced in there I wasnt gonna pull that out again to swap them. I went to hook everything back up and the harness didnt match up.

[carotman]

Ok, I measured the pulleys and the Carb pulley is 74mm and the EFi pulley is 69mm.

[Vanilla Sky]

probably to reduce parasitic loss on the carbed motor. that, or you have a hold-over from the last gen. could also be that one came with a replacement alt and isn't the OEM-sized pulley.

[Blkblurr]

What really matters is the inside diameter of the pulley. Where the belt sits. If it's the same then you're ok on the diameter. If you use a different size then what it came with, I would imagine your current output would be a little lower or higher depending on which way you went from the original pulley. One is 93% the size of the other. I beleive the one with the extra wire is for the FI model. I would think you could change the regulator and be good but I haven't tried it myself.

[carotman]

the circumference is smaller on the EFI pulley I had. It has the same number of grooves and the width and offset is the same...

This really makes me wonder where both pulleys come from. That'S why I need people to take a ruler and measure their pulleys.

[thegreatdane]

Isnt your B20A alternator pulley smaller in width than your A20 pulleys??

[carotman]

yeah it's smaller. I'm talking about the A20A alternators. I have 2 spare A20A engines here. I was comparing the alternators with the B20A and noticed that the 2 A20A alternators had different pulley sizes which was weird.

The B20A uses a completely different pulley.

[thegreatdane]

oh sorry I didnt notice that you said the pulleys were different too. I think the B20A alt pulley is the same as on the 88-91 civic/crx D16A9(ZC?) 130hp engines.

[Strugglebucket]

just measured my '89 efi pulley and i got 74mm.

[carotman]

Still waiting for some more measurements...

[Blkblurr]

I will measure my SEi today and let you know.

[carotman]

Soooooo.... ?

No one wants a cheap alternative to underdrive pulleys?

5mm may be small but will be noticeable. I honestly don't really care since I already have those 2 pulleys here and they will not even work on the B20A.

I'm trying to help you out guys but you got to help yourself too.

[rant]
Out of 5000+ members, only 1 took the time to take a ruler, open the hood and measure it. The whole process will not take more than 5 minutes. People complain about some members not sharing knowledge but it seems that no one is even willing to get off their ass to source that knowledge. Will I have to do this myself and spoon feed the information?
[/rant]

Ok enough with the ranting but I really need those measurements so we can come to a conclusion.

[Blkblurr]

Sorry man, I forgot. I will get to it today hopefully

[Vanilla Sky]

well, i have both sitting here side by side. the carbed one is smaller. i'll have to whip out a ruler and measure, but just by looking, it looks about 5mm different.

[carotman]

+

[Vanilla Sky]

i got 67mm OD for the DX pulley, and 73mm OD for the EFI pulley. one thing different is that the DX pulley is on a reman alternator whereas the EFI is a honda original. this in itself can be the difference. of course i'm not able to measure the ID of the pulleys, so i'm just measuring the lip.

[Blkblurr]

mIne is about 69mm. It's hard to tell for sure since it's hard to get to. It's definately close to 70mm though.

[carotman]

Well, so far we know that there were 2 pulley size available but still can pinpoint which pulley comes on which alternator.

Too bad people don't want free underdrive pulleys.

Since no one cares about this, I'm locking the thread. I'll know what to do next time. I don't have an A20A anymore anyway.

[A20A1]

What do you need, I'll try and help... I was just outside today making measurements and planning out how I will rotate my engine 90* to begin the RWD conversion mess I was discussing in a different thread.

EDIT:

I'm still looking for my alternator, I took my carb alt out of the car and gave it to another member who needed one... and never swaped it with an EFI alternator, hopefully I can find it I need it to run my car.

[carotman]

Well, I don't personaly need anything but I noticed that I had 2 A20A alternators that had 2 different pulley size. I was wondering why is that and from what car they came on.

Having a bigger alternator pulley means that the alternator will spin slower, acting as an underdrive pulley. AFAIK, people with a bigger sound system might want to have the smaller pulley and people that just want more power might just get the bigger one. Those pulleys are easy to find too.