Jump to content

Datsun 620 Alternator upgrades + my new way

Recommended Posts

OK, here we go...

(I know Slodat... I know! let my public flogging begin, I can take it!)

After MANY hours of reading through and searching for high amp alternator upgrades I have come to 3 main ways to do them. I tried to find the best layed out posts and put them all here along with wiring diagrams I could find and any other resources I thought relevant. Most are in the links below so I won't bore you w/ them here. It honestly isn't that hard of an upgrade but takes some thinking it through first to save you time and money. People have voiced an interest for a parts list etc, but sometimes what somebody did isn't going to exactly work for you.


KA24E upgrade by Icehouse

90 amp bolt with angled water inlet and KA mounting bracket



Saturn alternator setup by Mike Phillips

100 amp I think



GM Alternator Upgrade

105 amp according to specs from Schucks/Autozone

(couldn't find a clearly layed out walkthrough, if one exists lemme know I'll put it in here)


So after looking at these different options, I decided I didn't want to go find an angled water inlet and alt bracket and mess with coolant yet again this spring. That and I want the higher amp alt for when I want to upgrade the lights and stereo down the road so the KA alt upgrade didn't appeal to me


After looking at what limited space I have to work with I did not want to go with the Saturn Alt route, mostly because I really didn't want to grind down my steering coupler bolt since that is a grease fitting and I also did not want to take off the fan baldes/pully/radiator to get one little bolt off.


After comparing the alts I decided to go with the GM internal fan alt since it seems like the most compact and readily available and easily replaceable part.


I spent quite a bit of time looking through Autozone's site for alternators mostly because it was fast to change vehicals and lookup different alts. O'reily's site is horrible, though you CAN look up a part and it will tell you the other vehicals it will work for, so that would help when looking something up in a junk yard! I was mostly trying to find other alternators that would fit with out having to hunt down the V belt. I also used the Chevy S10 4cylinder (smallest engine) to help better match RPM's. Here is an incomplete, but good enough spread sheet since I didn't want to spend all night making this thing. At the bottom are alts for various Datsun/Nissan trucks as well.




I chose to go about the mounting a different way. Mostly I did it this way because It seemed the easiest way with out having to get a double V pulley because I didn't want to spend the time hunting one down.

Parts List:


This changed a bit as I tweaked it here and there all the hardware was found at Home Depot once I figured it all out:

7/16" 1-3/4" Nut for threaded rod as a spacer

(coulda bought 2 and cut the other but washers were better for fine tuning later)

4 3/8" lock washers

14 3/8" washer

2 3/8"x1" bolt (grade 8 for strength)

1 3/8"x6" 5-1/2" bolt (grade 8 for strength)


From the auto parts store:

105amp GM alternator (see chart but part# ULT 01-1433 from O'reily) $125.99 after core

4 pin plug - little bastard cost $35, so well worth searching for in a junk yard (part# BWD PT5674)

Battery Meter that plugs into the cigarette lighter (part# INN 3721) $19.99

15355 or 35.5 inch fan belt

V belt pully, Freebie from their alt tester drawer at O'reily.


The funny thing is, both O'reily and Autozone sell the Delco reman alts, but sell them as different names...All remaned in Mexico :( Yay lifetime warranty.



Takin' off the S6 pully and putting on the 1V pully


be careful of the axial force you put on these things. I had moved the shaft just a hair but putting force on it parallel to the shaft. It was enough to make the epoxy from the internal fan blade touch the case. A tap on the other end fixed the crisis.


- Make sure and use thread lock, as I wasn't taking chances with the nut being on there part way.



Pully comparison shows nearly identical radius to best match the RPMs



Side view of pulleys



All nice and tight with threadlock





So here is where I took a different approach. I wanted a solid mount and to get stuff to line up, this is what I came up with. I had an extra mount so I figured going a different route would be a good way to experiment a little. If I don't like it, I can always do something else.



Mounting setup from the bottom

5 spacer washers plus 1-3/4" spacer

(this can be fine tuned by adding/removing washers based on what pulley you have)



Near perfect alignment of the fan belt

I REALLY wanted it to be straight so I had to add/subtract washers a few times:



Front mounting bracket setup

I used and extra bracket from another motor

It isn't pretty, but it's functional:



From the top

I also tapped out the smaller hole to fit 3/8"-16pitch because I really wanted a solid fit.




More than enough clearance to the steering coupler






- As of yet I have not hooked up the plug to test, but I'm confident it will charge

- I want upgrade the grounding wire and Bat wire with fuse, because not doing so is just asking for trouble. The stock wiring was not designed for more than 3 times the load.

- NOT grounding the frame is just asking for it.

I'll post pics of that tomorrow, possibly tonight if I get the time, but it's already late, so probably not. I spent too much time putting this post togehter :cool:


This is for a '78 620 so the alt is internally regulated. If you didn't know already , the T connector is "L" and "S" for Lamp and Sense.

Looking at the wiring diagrams, both show the lamp (or "L" plug on the T connector) wired up the same

Sense (or "S" on the T connector) is the same and just jumpered to Bat


'78 Datsun 620 diagram



GM Diagram



Here is the 4 wire plug labeling

Don't use P or F, just L and S like on the stock "T" connector




Here is just a site with LOTS of info/specs on different alts. I think I got this from one of the other how to's at the top



CS-130 GM alt http://www.alternatorparts.com/cs130-cs130d-series-alternators.htm

  • Like 2
Link to post
  • Replies 26
  • Created
  • Last Reply

Top Posters In This Topic

Top Posters In This Topic

I've pinned this thread for it's relevant content. To keep it from filling with less than helpful comments I will delete them to keep it to the point.

Link to post

Great post!

How does the freebie pulley compare to the stock one in size? Can a stock pulley be used?

Well the stock pully on this particular Alt I got is an S6 or 6 ridge Serpintine belt so the only way it compares is by the diamater. I had the parts guy try to find one that best matched the diameter alerady on it. Now if the engine RPMs of the L20 match the vehicals entended for this alternator then we should be good. I made an educated guess by getting one for a stock S10 with similar sized 4cylinder engine. Is it right? I won't know until I hook it up, because it should start charging with load at idle. If it doesn't, the pully might not be matched well enough, but may be "good enough" if it starts to charge a little above idle. That's something I'll check once I get this wired up...probably tonight.
Link to post

well let us know :D



Charging at 14.9v at idle.

Charge light comes on with accessory click on key and goes off after it starts...just like it should.

Somehow I got it to idle at 500rpm, which it rarely does, but it was charging at about 13.5v at 500RMPs and at 800RPMs it was at the full 14.9v!


I added an extra ground wire to frame and a 4ga wire and fuse to the positive battery post post. It is way beefy but I didn't have anything better with out buying it. I plan to secure the cable to the body though to keep the vibrations and movement to a minimum. I probably could have done this better with a breaker instead of a fuse, but a high amp breaker was $30 and I didn't want to spend that right now. Having that much exposed + leads makes me a bit nervous, but with the fuse I feel safe from any catastrophic failure.





  • Like 2
Link to post

Dead Monkey

I dont want to be too much of a DICK here but is this a reverse Polish fuel system?


Looks like you have a Fuelpump regualtor is in the INPUT side of the pump? Is that right?Dont yu want the output!?



PS the alt conversion looks good. But as Ichouse says just grab a KA alternator and make a adapter to the T connector and your done.

Link to post

Dead Monkey

I dont want to be too much of a DICK here but is this a reverse Polish fuel system?


Looks like you have a Fuelpump regualtor is in the INPUT side of the pump? Is that right?Dont yu want the output!?



PS the alt conversion looks good. But as Ichouse says just grab a KA alternator and make a adapter to the T connector and your done.



You!? a dick? NEVER! :P

I am completely aware of the pressure regulator setup. I used to have a fuel pump at the tank, it died, I put the original in to see if it would pump, it did and I haven't got around to put it how it's supposed to be yet :)


And for the KA alternator, it wasn't no 100amp from what I read and I wanted the full Monte here.

Link to post
  • 3 months later...

this seems to be a good post to get some help from i have a 65 amp alt from i think a 240z i am looking for a bigger one for my 79 620 i have 3400 watts in stereo equipment in it with a optima yellow top ABE has alts from 110 amp -250 amp but start at like $160 -350 was wondering if there is something i could get off something at the wreaking yard that wont empty my bank trying to find something 150 amp or so for now thanks damon

Link to post

Might be a dumb question, but has any body tried building a bracket and putting the alt on the driver's side? If you have no a/c like mine, there looks to be alot of room ther for most any alt.


i was planning on doing that an running 2 alternators one for the truck an other just for my system but i am going to be using a york ac pump for my air ride system

Link to post
  • 9 months later...
  • 6 months later...

I thought I would add another alternator that can be used if your only looking for ~60Amps. As I said in my intro post I'm fairly involved in old subaru's so naturally I have a few spare parts in my garage. Today I finished putting the new engine in my 620 (the old engine's oil plug vibrated itself loose on the highway,within a few miles the engine siezed itself solid with no warning because all of the idiot lights were not installed when I bought the truck,anyway got a new engine and got it running).So I had the alternator out and I couldn't help but realize just how similar it looked to a subaru alt.So I looked through my pile o parts until I found a spare alt, and sure enough both the datsun and the subaru alt share the same mounting tab locations.The subaru alt bolts on with NO mods whatsoever other than converting the trucks wiring for a internally regulated alternator.The subaru alt even uses a single v pulley as well.The subaru alt basically just has a bigger case than the datsun alt,but its no so big that a angled waterpump outlet or grinding of the steering nut is needed.


so the short version:

alternator from ANY 82-89 Subaru and 89-94 Subaru Loyale


SAME mounting ear location

Same connector

NO MODS needed other than converting the wiring for internally regulated alternators.

Removes a piece with a very prominent mitsubishi logo and replaces it with hitachi,and unlike the carbs made by hitachi the alternators work for a LONG time.

Link to post

Right now I am trying to find a correct size belt.With my clutch fan a 34 1/8" belt is too short and 34 7/16 belt is to long.The 34 1/8 will fit if the lower mounting ear of the water inlet is removed.Not sure how I feel about that. I am trying to find a 34 1/4" belt...

here are some pics of the subaru alt compared to the stock 35 unit.NOTE: my parts alternator turned out to be only putting out 12.5 V,So I bought a new one for $55.


stock is the little one.



size comparison.



bottom mounting.





  • Like 1
Link to post
  • 3 years later...

What voltage are you guys charging at idle? My saturn alt is only charging at around 13v at 750rpm. I can increase the rpm but the voltage barely rises from 13v according to my voltmeter. Do I have a dud or do I need a smaller pulley? Im using a pulley that is roughly the same size as the oem pulley I took off the alternator.




Link to post

A smaller pulley is the same as revving it higher. If revving doesn't do anything neither will a smaller pulley.


Have you borrowed someone else's battery and tried it. No change would eliminate the battery.


What gauge do you have? Is it accurate? Maybe you don't even have a problem.


Have a friend jumper your battery with cables and leave his running. Don't start your engine but turn the key on and look at the gauge. Does it still read 13 or does the other charging system force it higher?



Ultimately does it really matter as long as the battery is charged by it???

  • Like 1
Link to post

Mantis, i have a stock alternator and sometimes when i have the lights on, wiper and heater it only reads like 12 volts or so. When i dont have those things on, it only reads about 14.5 or so. Do u ha ve a voltmeter hooked up? If so what does it read at driving like at 2k rpm?

  • Like 1
Link to post

The early trucks 521? were only 28 amp (I believe) the 620 is about 35 amp. There just isn't enough room for a larger alternator on a 620. If you are willing to make an adapter and mount, any size alternator you like can be fitted on the other side of the engine below the distributor. Use the threaded bolt holes that are already there for the smog pump. My 521 bolts broke off and a friend moved the alternator to the other side and it worked just fine. I didn't need a larger alternator but there was lots of room with the L engine leaning away to the right side. 

Link to post

Why not just drive over to your local auto parts store and get it checked? They can check for diode and regulator failure in addition to giving you a second opinion on your charging voltage.

Link to post
  • 2 years later...
On 2/11/2013 at 6:28 PM, gearhead said:

Right now I am trying to find a correct size belt.With my clutch fan a 34 1/8" belt is too short and 34 7/16 belt is to long.The 34 1/8 will fit if the lower mounting ear of the water inlet is removed.Not sure how I feel about that. I am trying to find a 34 1/4" belt...

here are some pics of the subaru alt compared to the stock 35 unit.NOTE: my parts alternator turned out to be only putting out 12.5 V,So I bought a new one for $55.


stock is the little one.



size comparison.









I will have to dig around for it, but if memory serves me, an Alternator for an 80's Cadillac ElDorado has the same mounts (180 degrees from each other) and is 100 amp. Not sure the distance between the lower mounting tabs or body circumference though.

AutoZone Image.


If someone has one of these laying around that's handy, feel free to comment what you find out. It will take me a while to dig for the one I have, if I still have it.

Link to post

I have one of those GM that's the 180degree. But the sense( 4 wire connector I believe) connector is filled with something so I don't know how it works. But it a perfect fit(least for a 510. It was sold from a The Z store in Washington but I never used it still in box.I got it for 40$ Look new but sure its a reman. If one can find brand new those things last forever. Get a TSI Automotive Denso starter. Youul be set for year. Not like every 8 months with a O rileys /Autozone starter alternator swap


Be honest I don't know why people don't use this one more often. But never knew what exact model it is. Never saw a real write up on this either. Its all the offset type with the wrong Lower Ear mounts.

Edited by banzai510(hainz)
Link to post
  • 2 weeks later...

Here’s a fun fact.... the alternator that’s factory in my 1990 trooper (2.8 gm v6) is the same alternator I’ve installed in my 620. It’s a cs130. The fit was tight but it does fit and it does work. 

 Correction: it’s a cs121(121mm stator diameter) 75-90 amp. 
 Closest thing I can find is a Pontiac lemans with the 1.6L. 
 GM came out with this CS line up in 86 and used them through 95. 

Edited by J's 620
Link to post

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...

Important Information

By using this site, you agree to our Terms of Use.