924Board.org

[BionicBalls]

Shortly after finding Smoothie's write up on his install on a 931, I decided that I was going to install one on my N/A. As luck would have it my alternator crapped out on me 2 days ago so the project got pushed to the forefront.

At first I considered buying the 931 alternator mounts and just re-positioning it, but time and money were factors that dictated that I keep it in the stock position.

I picked up an alternator from Auto Zone for $118 from a '99 Chevy Tahoe. It's offered in 105 or 124 amp. I got the 124 amp. There are higher amp ones available online, but they cost more and don't have the warranty that AZ has (lifetime). The CS-144 comes in three different mounting style (the 3.8, the 180 degree, and the 90 degree), I opted for the 90 degree mounting setup that comes in the GM trucks.

Step 1. Disconnect Neg Battery.
Step 2. Remove old alternator.

Now for the conversion and pics:



As you can see the 2 alternators are very similar in size. Bosch is on the right, CS-144 on the left.



The CS-144 looks a little bit taller, but I think it's just the way they are sitting in the picture b/c the belt lines up perfect.



The first real "problem" is that the mounting hole for the CS-144 is bigger than the 924 mounting bolt. I solved this problem by taking a piece of tube and cutting it down and hammering it inside the alternator hole as a spacer.

Another option would be to drill out the mounting brackets to the size of the alternator mounting hole. An M10 bolt fits perfectly. Of course, this can only be done if you have gotten rid of the stock rubber mounts and converted to some metal mounts.

Only the top mounting hole needs to be addressed. I didn't use the stock mounting bolt on the bottom.



Next problem is that the length of the mounting hole on the cs-144 is shorter than the Bosch unit. No problem. Just take the rear mount off the car and extend the holes backwards a bit. You can see the difference between the new holes and size they started at:



At this point I went to test fit the top mount and discovered that the corner of the back mount would not let the alternator mounting holes meet up. So I ground the the corner down a bit to allow clearance:





Now the top mount should slide in.



Now for the bottom mount:

At this point, I started getting close on time so I didn't take as many pictures. In fact I only took one, but it shows everything. Even my dirty ass engine. I need to change my valve cover gasket so it stops leaking.



Alright, so for the bottom mount I used the stock tensioner slide. I flipped over so the slide points downward. It's hard to see, but the slide part wits flush against the alternator and is used to distribute to pressure.

To mount it to the alternator, I drilled a hole past the slide. There is a spacer between the alternator and the bracket. This is to position the end of the bracket in the correct spot for it to sit against.

Now for the end of the bracket (The adjustment). In the stock form this is where the rubber mount with 2 studs bolts to (The other side bolts int he block). Well, using that mounting hole is pretty much impossible so You don't need that rubber thing anymore. I drilled out the hole in the bracket and then tapped it to fit an M10 x 1.25 x 30 bolt. The treads didn't feel too secure in the bracket from the tap so I welded a nut to the back side and that gave plenty of support. Next I screwed another nut on to the bolt before threading the bolt through the bracket. The extra screw will serve as a locking mechanism.

I then threaded the bolt as far out as I could while using the bolt from the bottom mount to pry the alternator away from the engine (thereby creating tension on the belt). The head of the adjustment bolt sits right up next to a large ridge in the block's casting that holds it in place. This is nice since it's a PITA to adjust and it holds the adjustment bolt tight while you tighten the locking screw up toward the bracket.

It should be noted that I have been using a belt 10mm shorter than the stock size and is what I \'m using with the CS-144.

Once mounted, everything lines up perfectly. and the belt is nice and tight.

The next step is the wiring which is the easy part. The CS-144 has a bolt terminal for the battery cable (These are the 2 heavy gauge wires coming from the starter). The single "hot wire" (mines black) is the ignition switched 12V. This wire goes to the "L" terminal on the alternator. You can accomplish however you want. They sell pigtails or I'm sure you can buy these tiny GM pin connectors. It was late when I did mine and nobody was open so I cut away the plastic connector and soldered a short length of wire to the L pin and then put a spade connector on the other end of it for the ignition wire. I then filled the connector on the alternator up with some silicone sealer to prevent any water from getting in there.

The ground is not needed on my car since I have all metal mounts, but I put one on one of the m10 bolt holes the corners of the alternator casing.

When looking at it, you couldn't tell that it wasn't a stock alternator. Overall a pretty easy conversion. It should be noted that I have my headers Jet-Hot coated to keep the heat in that area down. If your exhaust isn't coated then heat could be a problem. It's probably still a problem even with them coated. I haven't worked on fabbing up a cooling shroud for it, but it'll be in the works.
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1980 924 NA
1982 931

[BionicBalls]

Forgot the most important step: Reconnect neg battery cable and TIGHTEN IT!

I found that step out the hard way

Anyways, alternator is producing 13.4 volts at idle with the radio and heater on. Very happy with the upgrade.
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1980 924 NA
1982 931

[BionicBalls]

Another bit I have found:

A 35 ohm resistor should be installed in line for the "L" wire. This wire is the exciter wire and it comes from the battery light on the multi-gauge. The light bulb itself provides the resistance needed to tell the regulator to kick into action. So if the light bulb burns out, the alternator does not work. Installing a 35 ohm resistor is a safe guard against this happening.

I have just saved you hours of frustration that I have just recently experienced.
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1980 924 NA
1982 931

[Brendan]

[BionicBalls]

I completely removed the stock rubber bushings a long time ago. They were shot as most are. I replaced them with some random metal washers'bushings I had around the shop. I'm sure you can find something similar in the hardware bins at Lowe's and Home Depot.
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1980 924 NA
1982 931

[Brendan]

Aha. My bushings are actually just fine, so I've left them in there.

The resistor required is a curious thing. Some sources call for 35 Ohm, 3 Watt, others says 82 Ohm, 5 Watt. Radio shack has an 82 Ohm, 5 watt on the website, but I'm hoping to find one in the store. I am going to hit a couple Radio Shacks on the way home today, but if I can't find one, I am going to go with the Painless Wiring kit, #30707. Has a proper connector and comes with the resistor for $18. The plug alone at Autozone was $30.

[BionicBalls]

resistor has to be anything between 35 and 500 Ohms. It is the resistance that tells the voltage regulator to operate. This is known as exciting. The Cs-144 has an option for a self exciting regulator in which the ignition wire is not required. I think it's just a useless $30 option for our cars.

Your dash light will provide enough resistance on its own. Additional resistor is just a fail safe.
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1980 924 NA
1982 931

[ideola]

Nice job!!!
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erstwhile owner of just about every 924 variant ever made

[Brendan]

[BionicBalls]

[Brendan]

That's how I built mine, actually. I don't have a welder here. I've got some cut down and stubby 17mm wrenches. We'll see tonight how it works.

I'm hoping that I can pry the alternator case away from the block and just spin that nut by hand most of the way......


Brendan

[BionicBalls]

I spun it by hand most of the way. I'm sure this is obvious, but don't tighten down the top alternator bolt until you have the tension set on the bottom.
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1980 924 NA
1982 931

[Brendan]

So, it's been on there for a couple of months, and while I haven't put many miles on it (~30) it works great.

One question: What are you all seeing for voltage out of this alternator? I expected to see my factory voltmeter reading 13-14 volts after the swap, in stead of 10-10.5 with the old factory alternator, but it only jumped up to about 12v.

[BionicBalls]

I see around 14v unloaded to about 13.2 loaded.

Make sure your wires have good connections and good grounds.
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1980 924 NA
1982 931