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1969-1974 140 alternator conversion


Stößelstange über alles
Oct 12, 2016
I am well aware that The Swedish Embassy manufactures a kit to make this job easy. This article is not meant to undercut or disregard his reputable and well-liked product. My conversion (outlined below), uses the original B20 cast-in alternator mount and modifies the original tensioner/adjuster bracket. This is merely another way to complete this task.

Delco 10SI alternators are manufactured from cast aluminum. Unlike ferrous metals (steel, iron, etc), aluminum can be somewhat flammable/dangerous to cut using power grinders, grinding wheels, flap wheels, or other powered abrasives. It is CRITICAL that you use abrasives designed for aluminum to reduce the chance of fire. If you must use a cut-off wheel that is labeled ?for ferrous materials?, use a new one to prevent the steel filings from sparking and igniting the powdered aluminum. Always wear eye protection when cutting or grinding, and you should probably use a respirator too.

Here?s a good outline of how I did the swap. My 1971 142S came equipped with a SEV/Motorola alternator with an external regulator. While there is nothing inherently wrong with these alternators, they are difficult to find locally, and when you do, they are extraordinarily expensive. Enter, Delco (GM) 10SI alternators. Used on most GM products from 1963 till the late 90?s they are extremely common and therefore, very cheap. Another perk, besides easy of sourcing, is the power output. My stock alternator was rated for 33 amps! The ?low output? 10SI puts out 63 amps- nearly twice the power.

For my swap, I went to my local Advance Auto Parts (though any place will do) and told the guy at the counter I had a 1980 Chevy C10 with a 305 gas engine. I opted for the $58 63 amp CarQuest rebuilt unit with a lifetime warranty. I paid a $10 core charge upfront. I chose to use a 3-wire unit.


I went home and pulled my old alternator out. I set them side by side and began measuring. The original top (threaded) ear is flush on the front to the housing of the alternator, and roughly .5? thick. The 10SI has a small boss on the front of the unit which must be ground down flush. The boss on the backside can stay, as it will just add strength and more thread engagement.


The bottom mount is where measuring really matters. The boss on the face can stay, as the bolt will just tighten against it. The face to the rear of the original alternator measured 1 5/16?. The Delco is around 2? from the face (I avoided measuring/including the boss). Before you go ahead and cut it down, take an appropriate sized drill bit and open up the bottom mount hole to allow the original bolt to slide through. It?s better to do this while the ear has 100% of its structure. To remove the extra material, I used a sharpie to mark how much of the backside had to be cut off, and then used a cutoff wheel to slice it off. I then used a coarse file to true and smooth all the edges.



The final ?fab? portion requires adding ?? of spacers to the front of the slotted top bracket where it originally mounted in the block (blelow the t-stat). Then add a short piece of steel on top of the shims/spacers and drill a hole that is close to where the large 7/16? hole is close to the thermostat. Run a 7/16-14 tap through the threads to get any filth that has built up over the years out.


Wiring is fairly straightforward. Determine which wire from the old alternator connects the AMP light by connecting it to the positive battery terminal and seeing if the light comes on. This will go to the small spade post on the left ?T1?. Use a test light to determine which wire on the alternator connects to the battery. Mine was a big red wire with a ring terminal, so I retained the original connector because the 10SI uses a nut/ring terminal for the charge wire. Finally, run a wire from the right spade terminal on the unit ?T2? to either the fuse block, battery, or somewhere with high voltage drop. This is your signal wire for the alternator.

Put on and adjust your belt, and you?re good to go!