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Eagle Eyes
1,334 Posts
Discussion Starter #1 (Edited)
I have finally finished my quest of fixing this poorly designed alternator setup for the 6.2L Diesel vbelt driven models.

As it is well known and documented here, the stock alternator has belt slippage issues which causes squealing and lack of charge.

GM had contacted Gates at one time and had them develop a special application belt, Gates 5725, this, in most cases, does help reduce the squeal/belt slippage and often eliminates it or most of it.

It also seems that belt tension, even with the upgraded belt, suffers from the alternator slowly de-tensioning. I believe this is largely due to the belt whipping that occurs on the 6.2L Diesel. Constant re-tensioning of the belt is often needed, and some with the result of eventual breakage from continual stretching.

As mentioned in a previous post, I attempted to solve many of these issues with a dual belt pulley upgrade made possible with the modification and installation of military HMMWV crankshaft and waterpump pulleys. This has been a complete success with no issues since installation, and found here: https://www.dieselplace.com/forum/63-gm-diesel-engines/20-6-2l-diesel-engine/770361-oem-3-groove-hmmwv-4-groove-dual-belt-alternator-modification.html

However, because I was still running a 12SI 66amp alternator I’ve been struggling in keeping the battery properly charge and having the power needed in certain “stock” cases such as high beams and full fan on at low idle. I had the 66amp installed for years due to the issues above I know I could install a 78amp model, however, based on the 12Si power curve it would only put out 40amps for that situation which I believed to be inadequate. The power curve is correct as I tested it and came up with my digital meter reading less then 12.3V and my clamp on ammeter was reading around 30 amps.

I also know there is the special option (still Delco Remy 12SI) 94 amp alternator, not typically supplied to the 6.2L and would only put out 50amps in those conditions. However, it has been proven the higher amp and even higher custom amp 12SI’s do not hold up in the long run due to heat and the design’s inability for cooling.

I decided it was time to do an alternator upgrade, with faith in knowing my dual belts could handle a larger amp alternator. Reading that the CS130 has reliability issues, and determining that the amp increase was not worth it, I settled on the reliable CS144. At the same time, I decided to install what I have been mulling around in my head for years- a belt tensioner- as I have always disliked the factory method.

I always liked the outside appearance of the 12SI and not the newer style alternators and the CS144 which in looks like a beefed up 12SI. This larger appearance is true, in that it is physically larger. And, the benefit that the 140amp model puts out 95amps at low idle!

----The CS144 Alternator Installation----
Online, I found only three owners attempting to swap in a CS144 into a 6.2L. Two stated no issues, that they loosed the brackets and slipped it in. One stated he had to replace the heater hose nipple at the crossover with a 45 pipe fitting to reroute it away from the upper bracket, and trim that bracket for clearance. Clearly it can be seen what he meant, the heater hose, nipple, and a small part of the crossover sit directly above the alternator top bracket where it goes down to the intake bolt.

My attempt provided mixed results. To do the dual belt pulley I had to space out my brackets with three washers, to align the alternator pulley with the water pump and crankshaft 4 groove military pulleys. Installing the CS144 in this configuration provided a tilt and misaligned the belts. Surprisingly, I had to remove all the washers and put the brackets to stock placement for alignment.

The lower bracket I unbolted and pushed downward, which moved little to none. The upper bracket was the issue, fully up it hits the crossover and hose. However, since I planned on using a smaller bolt to give me a bit more clearance (CS144 uses 10mm so I used 5/16) the clearance needed was almost achieved at that point. I did grind out an arch into the upper bracket to clear the crossover, but left the hose and nipple stock. This is tight against the hose. With that done, and using a 5/16 bolt, clearance was “barely” met. I feel the undersized bolt is okay to use as I believe it is doing more of a clamping then a holding of weight as the lower bolt does. In the end I used a flanged grade 8 to help prevent any bending of that bolt, and a thick oversized washer to secure against the factory adjustment arch. You will see with the tensioner that lockwashers and spacer washers were also used for that.

The back of the CS144 has one or more mounting holes, like the 12SI does. None directly mounted with the 6.2 lower bracket arm. However, with the alternator clocked at “1:30” which provides both the terminal and plug upwards, one mounting hole comes very close. The arm sits against the casting. I was able to make a simple spacer to join the bracket arm to the alternator, using one bolt to the alternator body and two in the stock bracket (see picture). Some people online chose to not do so, I feel that it’s a mistake not to as the CS144 is significantly heavier.

Otherwise, I did have to use three washers to space the 6.2 lower bracket correctly, placed between the bracket and alternator (not at the block as previously done).

Naturally, a heavier charging cable is also needed. The CS144 upgrade is popular for many applications, and I saw most online opt for a 4awg power cable, while the Delco Remy catalog specifies 2awg for up to 4’ length for a 140 amp alternator. The price difference is slight, so I made up a 2awg welding cable currently at 4’ to make room for any future upgrades.

A wiring adapter is needed to adapt the 12SI truck harness to CS144 plug. See details in the short list below.

At the same time I upgraded my side posts connections by heavily trimming away the plastic on the terminals, and installing stainless steel internal hex setscrews and flange nuts with nylock so that one can install or pull off the cable without messing with the stud itself (credit given to a Dieselplace member I can’t remember). I experimented with an old battery and those sideposts can handle at least 200inlbs.

In short:
--Obtain/build a 3-4’ 4 or 2 awg cable, 3/8 end for battery, 5/16 for terminal.
--Obtain 12SI to CS144 wiring adapter. Found many places, for reference if you have instrument lamps: Delco 8077/GM 12083462 if you have gauges (needs resistor built into the adapter) Delco 8078/GM 12102921.
--Obtain CS144 alternator. For example, Napa “RAY 2134625G” which is a 2nd generation (supposed better bearing and reinforced casing, witnessed by rear bearing cap), standard pulley (some are tapered) and has an unthreaded top ear (this provides some clearance and most of our 12SI strips out anyway). This model is a standard stock item at Napa unlike other models.
-- Remove pulley and swap to your single (slippage guaranteed) or preferable dual belt pulley. This time I used an impact which made quick work of it. When I did my dual belt in the past I think I used a old impact socket and place vice grips on the outside of it and a hexkey through the socket- hard but not impossible and it wrecks your socket.
-- Reclock alternator. Unless you get a 1:30 alternator, reclock it. When new/rebuilt its simple. Undo the four case bolts. Do not separate as others have mentioned. Have alternator pulley down on bench, firmly hold back section, use rubber mallet to tap on bottom ear. It will easily rotate to your desired position. I felt 1:30 is best as keeps the terminal and plug upward and easily accessible. Otherwise, it is pointing to the engine, downward to the bracket, or to the fender which may hinder turbos (Banks especially).
--Test fit the lower bracket to see washers needed to space, and make simple spacer to mount bracket ear to back of alternator case.
-- Loosen lower alternator mounting arm to see if it will go down any.
-- Remove CDR and bracket.
-- Move top bracket upward and test fit alternator. Trim bracket at crossover if needed. Hopefully this is all that is needed.
-- Install alternator with top bracket loose to help swing. Install plug adapter and charging wire at this time, slide alternator inward and tighten bracket when swing is achieved.
--Reinstall CDR, install belts, tension.

----TFLundy’s 6.2L Diesel Alternator Tensioner----

For years I’ve imaged how handy a tensioner would be on this engine. I had seen no mentions of it online, and only one set of pictures on here of one of Turbonator’s engines where it appeared they cut the bracket, welded on a pipe and used threaded rod with a bracket on the alternator to tension. Those two pictures inspired me more.

I took some time to look at different styles and much time staring at the factory bracket. I wanted to do one that was simple to make, looked factory, was clean and easily installed and used.
I saw online that the DMC DeLoreans (think Time Machine) apparently have tensioner difficulties and someone figured out to use a simple turnbuckle style. https://www.deloreandirectory.com/articles-and-stories/delorean-alternator-tensioner/ While we do not have a fixed point to do so, I figured out that by making a simple bracket out of angle iron that I could place it on top of the top alternator adjustment bracket, use the two bolts there to secure it, and have the stationary point we need. Some trimming on the back would allow access to the tensioning hole, while some French curves on the inboard side would allow for a turbo drain plug in the timing cover while keeping the bracket stout.

By chance, the identical parts listed in the DeLorean project was the same I used. 5/16”ID thurnbuckles worked for my CS144 but I believe would for the 12SI as well.

I used a piece of cardboard as a template to figure how far my stationary point (and overall length of the bracket) should be. In the end, thankfully, I made it so that I could manipulate the alternator by hand (or use adjusting hole if need be, but it was not) and have the turnbuckle fully collapsed at that point, so that full tension would be achieved with the most threads in the coupler.

The coupler is aluminum while the ends are steel or stainless (which I opted for) and anti-seized. The coupler comes in different lengths; this one is 2” long and is not through drilled. Test fitting showed that it took 17 turns for the thing to be fully disengaged. By placing the tension start position at what I could manipulate the alternator to be outward, my placement ended up with VERY tight belts in only four turns.

In only four turns the belts are tighter then anything I could manage with the factory method. In addition, I believe this style of tensioner gives a third point of resistance to the belt slacking problem. That is, if the belts are pulling the alternator towards to waterpump pulley, in effect reducing tension. The tensioner in this location prevents that. In addition, by placing the tensioner with the left-hand thread inboard (marked with a line) any motion in that direction simply causes the tensioner to tighten on its own.

Installation proved easier then expected. I assembled the tensioner fully collapsed, then bolted and torqued it to the bracket-using two or three washers to provide space for the coupler to move as it sits against the bracket. I then placed it to the top of the alternator bracket and slipped the alternator bolt through it and through the alternator ear at the same time. Then, move the entire assembly and alternator outward until the two top bolts line up and bolt it down. Tension the top alternator ear just enough to fully engage the tensioner yet loose enough so that the alternator can move.

At that time you will have the bracket fully installed, the tensioner fully collapsed to the alternator and bracket. Then simply rotate the coupler under desired tension is achieved. In this method it is very possible to overdo the tension. Of course, then lock town both top and lower alternator bolts.

In short:
-McMaster 59915K23 RH ball joint
-McMaster 59915K23 LH ball joint
-McMaster 8419K12 connecting rod/coupler/turnbuckle
-McMaster or other angle iron, I used 1/4 thick (OEM bracket is .20thick) 2”x1 1/2”x6”
-Thin cardboard for template, cereal box type
-Clear piece of mailing envelope to mark CDR bracket holes to transfer to angle iron
-You might need longer CDR bolts, my outboard was long enough, the inboard was too short.

Now, if we can only make one for that dreaded power steering pump!


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Added to 6.2L DIY

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Now you need to fabricate an alternator cutout when you punch the throttle. And /or a cruise cutout to improve mileage. Hmmmm?

Make an AC cutout as well. Those actually work really well on small engines except when climbing long hills.
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