Carpokes Porsche Forum

shoggr wrote: Thu Nov 07, 2024 11:26 pm Hi all just adding in some research I did into my 968 alternator replacement and if it saves someone some time on other forums or if its useful. A few options I looked into from others opinions:

Replacement with the BOSCH AL170X
Most expensive option but easiest option

Install the 1997 Nissan Quest Alternator
Requires modification to the support arm
Some washers and spacers required
Some minor alignment works to the mounts
Replacement pulley required
Replace with slightly smaller Ribbed Belt
*some users prefer this for 944 Turbo

Install a Pre-2000 Ford Mondeo/Scorpio Alternator
As far as I can tell no modification to the support arm
Replace with slightly smaller Ribbed Belt
Only 70A units available..?
Some models you can reuse the front of the stock/AL170X casing.
*Preferred for 944 due to 70A

Install a Ford G3 Alternator (7774 variant)
Appears it will need modification to the support arm
Requires a replacement pulley
Some minor alignment works to the mounts
Requires a specific voltage regulator (non-LRC)
*appears for a 928 this would work as direct replacement with minimal work

Refurbish (DIY) original generator or a AL170X
Cheapest, not too difficult but requires some effort
Requires some tools and some replacement parts

Summary
In summary once adding in all the cost of parts (considering new not used), it works out 50% cheaper to refurbish the original unit or a AL170X compared to other alternatives and about 70% cheaper than buying a new AL170X. The other options may be desirable if you have a Turbo 944 and want to reduce space issues (for a larger turbo) or want more than 115A and has an internal fan/better cooling.

Below are some steps I took on the refurbishment and some lessons I learned.

Tools:
Philips Screw Driver
Rubber/Nylon Hammer
Gear Puller
Solder Iron & Soldier (if replacing Diode board and slip-ring)
Brake Cleaner/Contact Cleaner (if dirty)
Miltimeter (for testing diode board)
24mm Socket (preferably cutout for the hex key, if not then maybe a vice)
8mm Hex Key

Parts:
6303 Bearing (rubber sealed, don’t cheap out on these get NSK)
6201 Bearing (rubber sealed, don’t cheap out on these get NSK)
Slip ring – ASL9006 e.g. ( https://www.ebay.com/itm/133445646891 )
Voltage Regulator (HB353 or IB353 or original porsche/bosch etc)
Case Screws M5x110mm or M5x120mm (if you need to drill them out)
Rectifier - 0120468001 (optional if original working) e.g. (https://www.ebay.com/itm/271836200121)
Bearing tolerance ring (if you break yours) e.g (https://www.ebay.com/itm/133445646891)

Alternatively you can just buy refurbishment kits with all these parts (excluding the diode board) from ebay under AL170X or “Porsche 944”

Steps:

Remove alternator from the car (follow the cars manual)
This involves removing the belt and the 2 mounting bolts in a 968 (can be done without removing the air intake/water hoses or the throttle but the MAF needs to be removed).

With the alternator out for the car, you will need to undo the 24mm Nut, you can use a vice and a 24mm socket if you do not have a cutout, use the hex key and loosen the nut (this can be challenging)

Remove the 4 case screws (these can strip as they are terrible quality, drill them out carefully if you need to)

Once the case screws are removed you can separate the unit, do so carefully and tap with a rubber hammer to remove (ensure you have removed your voltage regulator first as this will get damaged)

When carefully pulling apart be careful not to damage the bearing tolerance ring located at the bottom of the alternator (near the voltage regulator end), these are fragile and one more part to replace if damaged.

Once separated (one half will have the shaft and the other half will have the winding and diode board), we should start testing the diode board and windings before proceeding. For the windings use one probe on the milliliter (set it to Ohms) and measure from the 4th wire (clockwise) and put the other probe on the first wire, record the number and so forth for the 2nd and 3rd, these numbers should be close to 1.2 Ohms and match each other, if this is ok then your windings are fine and ok to proceed (if its not ok then no point proceeding and get a proper test done as this might be damaged).

For the diode board this video would be more useful than anything I can write:

If the board checks out ok the no need to replace

Before replacing the diode board we should check the shafts connection to see if there are any faults here, if there is then it is not worth proceeding. To check the shaft you can simply do a continuity test on the multimeter, set the multimeter to continuity and then place one on the first ring of the slip ring and one on the 2nd ring (if the slip ring is damaged you will need to remove this carefully with a gear puller after you remove the bearing and test the bare wires), if it has continuity this is ok or you can also do an Ohms test to confirm, it should be approx 3.8 Ohms.

If all ok, unscrew the diode board and replace and soldier in the new board to the windings (be careful not to ground the windings by accident (can do a continuity test to the casing and ensure there is no continuity) also be aware when you remove the diode board there is a plastic spacer on the terminal for the battery and battery check light, please don’t lose this or forget to install otherwise you will short your alternator and damage the diode board.

Once done, that is 1/2 complete.

Removing the shaft, with the other half you will need to unscrew 4 screws (located near the front under the cooling fan), with these removed the shaft will come lose, once lose you will need to use your gear puller to remove the bearing and collar, once done replace the bearing and collar (you might need to remove a woodruff key if it was installed)

With those items complete the hardest part is replacing the slip ring, this is tensioned onto the shaft by a tight fit, you will need to remember which wire was for the top of the slip ring and which was for the lower, it is fragile work on those wires. The upper ring wire runs through the gap in the centre of the slip ring and then is fastened into the hole in the slip ring to make contact (could soldier a very small piece in the edge hole), the lower is the same but from the bottom, I suggest using some shrink wrap on the wires to ensure they are isolated but not necessary if they look fine.

Once completed, re-assemble and should be good to go, if you do drill out any screws ensure all the fragments are brushed away before assembly.

dr bob wrote: Fri Nov 08, 2024 9:15 am All great info!

A dozen-plus years ago I replaced mine (same in my 928) with the AL170X Bosch rebuilt, chasing some charging issues that turned out to be something different. I was running out of options and replaced the alternator even though testing was saying I didn't have an actual alternator problem. And I didn't. The battery ground strap was seriously corroded inside the insulating sleeve.

My original alternator with maybe 90k on it came out, and I replaced worn parts before bagging-tagging and putting it in the good-spares bin. The guidance you share on parts would have been seriously valuable, vs. chasing pieces down from local rebuilders. The bearings were the easy part. The slip rings the hardest at least in my case, and I had a local specialty rebuilder install and finish the new ones for me.. Rectifiers were fine. All good now.

From your mention on the case screws, I do suggest that folks use an impact driver on them to avoid the damage. The combination of the hammer impact and the torque applied made short work of getting the screws loosened with no head damage. This isn't your battery or pneumatic impact gun, but the hammer-driven hand-tool version.

Users should note the 120A rating on the original Bosch alternator used on later 944 and 968 cars. That really rules out some of the lower-rating options that might otherwise bolt up, especially if you have extra power consumers installed. Also note that many otherwise bolt-up alternators aren't really capable of the higher RPM duty they will see in a 944/etc. As an interesting aside, my 928 with auto gearbox has a different pulley arrangement to speed up the alternator even more, in consideration of the abundance of low end torque available. My tach has virtually no wear above the ~~3k mark, somewhat validating that factory assumption. I drive like an old white-haired guy these days, because, well...

Meanwhile, for the obsessed, Greg Brown at Precision in Orange has been making a $$$ replacement using modern Porsche/Bosch guts in a custom-machined case, and it's a drop-in replacement. It has much higher output capability, and offers slightly less heat loading per output watt than the original. It comes with a modern overrunning-clutch drive too, interesting for frequent high-RPM shifts that I don't do in the 928. But the 944/etc. crowd likely does. You'll need to upgrade some primary cabling for the added capacity. Extra cooling will help a lot too.

Aaron_N wrote: Fri Nov 08, 2024 1:26 pm I went the Nissan Quest route with the aftermarket relocation bracket. The main reason was to save weight, but the numbers turned out much less than expected. The Quest alternator is 2.4 lbs lighter than stock, the bracket 2.9 lbs lighter than stock for a grand total of 5.3 lbs of savings.

If the aftermarket alternator lasts, it will be worth it. If it doesn't I'll probably rebuild my original.

shoggr wrote: Fri Nov 08, 2024 1:40 pm

Aaron_N wrote: Fri Nov 08, 2024 1:26 pm I went the Nissan Quest route with the aftermarket relocation bracket. The main reason was to save weight, but the numbers turned out much less than expected. The Quest alternator is 2.4 lbs lighter than stock, the bracket 2.9 lbs lighter than stock for a grand total of 5.3 lbs of savings.

If the aftermarket alternator lasts, it will be worth it. If it doesn't I'll probably rebuild my original.

I was very tempted by this option as well, I would of gone this way and I liked the internal fan of the Quest alternator but I just got the engine back together from a rebuild and it failed not long after so I didn't want to take parts off again I didn't need to to get the notch cut in.

If I have issues in the future I will go this route, I feel it is the better of the other 2 alternative options and I appreciate adding in your experience that is very positive to hear and seems reliable so far which gives me more confidence.

Tom wrote: Fri Nov 08, 2024 1:44 pm

shoggr wrote: Fri Nov 08, 2024 1:40 pm

Aaron_N wrote: Fri Nov 08, 2024 1:26 pm I went the Nissan Quest route with the aftermarket relocation bracket. The main reason was to save weight, but the numbers turned out much less than expected. The Quest alternator is 2.4 lbs lighter than stock, the bracket 2.9 lbs lighter than stock for a grand total of 5.3 lbs of savings.

If the aftermarket alternator lasts, it will be worth it. If it doesn't I'll probably rebuild my original.

I was very tempted by this option as well, I would of gone this way and I liked the internal fan of the Quest alternator but I just got the engine back together from a rebuild and it failed not long after so I didn't want to take parts off again I didn't need to to get the notch cut in.

If I have issues in the future I will go this route, I feel it is the better of the other 2 alternative options and I appreciate adding in your experience that is very positive to hear and seems reliable so far which gives me more confidence.

I installed the Nissan alternator on my 944 Turbo purely to make room for the turbo and MAF. If I didn't need the space, I wouldn't do same alternator again. The quality of the Nissan alternator is no where near the original, especially the rebuilt units sold on eBay.