I wanted to kill the 3-4k rpm belt squeal from the water pump slipping on my 79 Rx7 due to the air pump having been removed. The belt is pretty new, very little runtime on it. Ordered a Banzai Racing pulley kit with included belts. Pulley gets here, and it doesn't fit my alternator because my alt has two flats on the shaft. This is apparently not even common on all 79 rx7s according to Banzai Racing.

That sounds about par for the course when it comes to owning a 79.

As I'm figuring out what my options are, I think back when I was setting the timing. My timing light would read battery voltage. Engine running, even giving revs to 3-4k rpm to see if the voltage changes, I'd see 13.0 average volts and 13.1 peak volts. That's barely charging. Is that standard for a 79 alt with an external regulator or does my reg need adjusting? Plus I've got a wideband and an upgraded fuel pump increasing current draw. Fantastic, I'll just upgrade the alt to compensate for the increased electrical draw, delete the external reg, and fix the belt squeal all at once.

So, I order a brand-new, 89 turbo alt, thinking I need the turbo alt for whatever reason. (I realize now that the only difference between a Turbo and NA alt is how the wires mount to it.) Anyway, the alt gets here and the company that manufactures them makes them with a 17mm shaft, so my pulley doesn't fit this alt either. I returned it and am waiting for a refund. I was thinking of getting a remanufactured 89 alt, instead, to help make sure I get the 15mm shaft. Did some looking around on the forum and I'm seeing quite a few posts complaining about remanned alts failing prematurely. Is this the general consensus 15 years after those posts still?

 

89 and later alternators all have 17mm shafts. You can buy quality remans or crappy remans. You can buy a new alternator,which is route i would take.

The latest(bolt in) alternator that has a 15mm shaft is an S4 which would have come on 1986-88 RX7 and rated at 70 amps and should provide you with enough power if your only aftermarket component is the fuel pump you describe. They can be had from rebuilders in larger amp ratings if you have more aftermarket accessories like an electric fan.
When you get up past 70 amp alternators you need to upgrade the alternator output wire and main fuselink or fuse to accommodate the extra current alternator can provide.

Hope this answers your questions without further confusion.

 

Did you see this thread? Might be helpful.

https://www.rx7club.com/1st-generati...pgrade-967330/

As GSLSE describes above, I am running an S4 NA alternator for a direct bolt in to my FB.

 

I'm running an S4 on my SA as well. Plug and play, no changes needed at all and get an extra 20 amps or so from stock. Also it sounds like your alt was not doing its job very well for whatever reason.

 

Really? The Banzai Racing guy was very adamant that all factory alts up to '91 have a 15mm shaft.

I was fine with running new wire and everything to the battery either way. Probably safer. And you shouldn't need to upgrade the fusible link since it doesn't have to go through it.

That's a useful thread, thank you.

 

While I don't know for certain details concerning the shaft size changes, the reason most people go with an S4 alt is because it doesn't require any electrical changes. Of course for a 79 you'll need to do a few extra things, but that's all covered in the thread tommyeflight89 linked.

For the S5 a change was made from the earlier resistive type to a sensing type (whether those are the correct terms I am not qualified to say). Specifically this change meant that the alternators require different wiring going to them. Some people do this wrong which then leads to battery drain - I recently rewired mine to remove the relay and no, you do not need a diode or relay. I chose to go the S6 route for 100 amps given that both it and an S5 would require rewiring regardless.

Summarized this would be S1-S4 (excluding 79) have the same wiring and are plug-n-play, and S5-S6 require some simple rewiring but are easy to make work. If you're going to be rewiring things anyway I might consider an S6 alt (unless you want to use the pulley you already have) if the prices are similar.

 

I wish I could find some definitive confirmation on the shaft sizes. Maybe I should have just had my pulley bored out to 17mm. . .

I knew about the s5 and later alts needing to be wired differently. I wanted the 80 amp alt as I'm hoping to go electric fan and stereo someday.

I read that all you needed was to run a few jumpers in the car-side plug of the voltage regulator to make an s5 alt work fine, as well as the dash light and voltage gauge on tach.

Is this how you went about it?

 

You did get definitive confirmation,here's some more that no one else has mentioned. Belts that came in pulley kit you got won't work with your intended alternator choice,they will be too short. Kit is meant for S4 and earlier alternator. S5-S6 alternator case is larger/wider,means shaft centerline is farther from e shaft and requires longer belts.

 

I put a double pulley on my REPU and had to get the bore enlarged at a machine shop. I did not get my double pulley from Banzai.

 

The kits Banzai Racing sells are for 79-91 alt (a 15mm pulley) or FD Alt in a 79-91 car (a 17mm pulley) and both kits come with the same size belts unless the FD alt pulley kit is going on a car with an 89-91 water pump housing. That's the only thing they list that would change the necessary belt length.

If the alt shaft is farther from the eccentric shaft centerline, wouldn't that just mean it would see proper tension lower on the adjuster?

I think I'll order a remanned 89 alt, and if the pulley doesn't fit, I'll have it bored out to fit the shaft.

 

I tried multiple on mine before going with a chevy 1 wire alt.

 

The issue is that lower on the adjuster is not always an option - definitely wasn't for me. I too purchased the Banzai dual belt FD alt swap kit as well as their bracket and the belts they provided were too short to even have a chance of working. I do like their pulley and tensioner but it would seem I'm not the only one who's had this issue. Some say it's because the alternator isn't the right size, however it's a reman FD alt so...? I find it hard to believe that could be it. I also have the stock 12A water pump and all so that's not either. Just be aware that you many need to get longer belts.

I might be crazy, but I seem to recall that the pulley has different backspacing in addition to the shaft diameter change between S4/S5. Don't quote me there, but it might be something to double check with other sources. It sounds like others have bored theirs out with success so perhaps that's not true.

 

I wish I had checked belt alignment with the new 89 alt I ordered, and then just had it bored.

Hindsight being what it is, of course. Haha

 

Ordered an '89 NA remanufactured alternator. Banzai Racing Pulley and the belts that came with the pulley kit fit perfectly with no modifications.

Very easy install overall. (Minus the stripped threads on the top ear of the alt. Nothing a drill bit, a tap, and a larger screw couldn't fix though.) Not quite as clean as I would have liked as far as wiring goes, but eh, it works. Lost my voltmeter in the tacho. I was prepared to go without that, though.

We'll see if the squeal goes away when I get it running tomorrow. Looks like a bad fan clutch if it doesn't.