GM 10SI Alternator Upgrade for Triumph TR6

Like many, my car still wore a Lucas alternator until recently. Unfortunately, the alternator was really showing its age. In normal driving it kept up reasonably well. However, I have an electric cooling fan, fog lights and a radio and amp in the trunk. With any combination of those things on, it quickly showed it was incapable of keeping up. In spite of the terrible Lucas reputation, that alternator served me well for 24 years and a spectacular amount of miles.

I decided to upgrade my car and started researching what alternator to go with. There are several options out there. What I found is:

- Plug N Play options which are becoming hard to find and could be pricey
- Inexpensive options which require some modifications but are plentiful

I searched for the Plug N Play Ford Fiesta Alternator and despite links sent to me by friends and chasing a lot of different leads, I never got my hand on a good alt. I actually at one point ordered one from a vendor in NY, only to have it arrive and find that it had the wrong casting to mount to a TR (though the photo on the website showed the correct casting). The scarcity of this option pushed me away from it.

I then went looking for Instructions on how to go down the inexpensive/plentiful path that required some modifications and engineering. Once I finally found a couple websites that had some good ideas and instructions I dug in. Here are the links I followed.

www.mntriumphs.org/aOLD/Tech.../Delco_Alternator_Conversion.pdf --- Excellent How-to that covers the '73 car and a Delco Alt (Much credit to the author of this document, as I followed this one very closely to convert my car)
www.vtr.org/maintain/alternator/conversions.shtml --- Some info from Dan Masters on several years, and several different examples.

To start, I had to remove my old alternator. I also cut loose the old connectors. ****** Before doing any of that, I disconnected the battery****** I decided to leave approximately 2" of wire on the connectors just in case I ever wanted to reattach them for some unknown reason.

The alternator I decided to use is a Delco 10SI alternator. This is a very good choice as it puts out 63 amps max. It is also good because it starts up at a lower shaft RPM than any other Delco alternator. That makes a difference!

The particular model/part number shown is clocked with the connectors toward the block. I re-clocked the connectors down so that washing the engine bay would not fill the alternator with water.

This alternator came with a pulley for a 3/8" belt. Not a problem if you have a later car or have replaced your Harmonic Balancer at some point (seems like only the 3/8" is available now). However, my car still has a 1/2" balancer. To make this work, I went to a local alternator shop near work and they found a pulley for a John Deere which fit perfectly. It is slightly larger (20% larger in circumference) so it runs the alternator a little slower. I did some math in a spreadsheet to ensure that it would still spin the alt shaft fast enough to produce the power I needed.

Next up, I had to modify my alternator. The stock Delco alternator has a mounting tab on the bottom with a 'boss' that sticks off the back approximately 3/4". I cut that off per what you see in the photo with my angle grinder with a cutoff wheel in it. I dressed it flat and perfectly straight with a file. That spacer is sticking out of it slightly, but it normally is inside.

I tried the alternator on the car, but found it would not mount up because the front engine plate edge was in the way. I had to grind the plate. Again I got out my angle grinder and used a grinding wheel to cut it down to size. I protected the engine bay while I did this as sparks were flying every where. I did paint it with a little black paint afterwards. It sure looked better in person (somehow everything I do looks worse when I take a photo of it....

Finally, it was time to mount the alt. The MNTriumphs PDF talks about making a bushing to size up the alternator to fit the 5/16" bolt that fits the block alternator mount. I cut a piece of old steel fuel line from the car the length of the alternator mounting tab. Then I split it lengthwise on one side and tapped my 4" long 5/16" mounting bolt down through it. It was a perfect fit and made a perfect fit to bush the 5/16" bolt up to the 3/8" ID of the alternator mount tab.

I mounted up the alternator and fitted the belt to the front of the car.

The MNTriumphs PDF suggested the use of a turnbuckle as belt tensioner. I bought a stainless steel version (only the screw eyes are stainless, the center is alu). So far this setup is working quite well. Time will tell if lasts. Adjusting it is really nice and much easier than the stock adjustment that a TR normally has.

To wire mine up, I followed the instructions at the MN Triumphs PDF. I connectorized everything and covered them all with heat shrink for additional protection from shorts. The main power connections to the car come from ring connectors off the back of the alternator. (I plan to reconnectorize these to make them look a little better). I sourced some 10ga wire at Napa and ran a third brown wire from that power terminal to the power terminal on the starter. This is to protect the wiring harness from the higher power of the 10SI alternator.

A word on Belts......

Since I changed pulley size slightly from both the original Lucas and Delco alts, and because the casing of the Delco alternator is a different size, I had to find a different belt for the car. I'm a bit embarrassed to say that I went through 5 different belts before I found just the right length for the car. However, I really wanted this length to be correct and the fit to be right. Getting it wrong would put the alternator too close to the engine and subject it to more heat than necessary. Doing so also put it much too close to my #1 spark plug and my fuel line.

I also found that there are some pretty huge differences in belt quality.... I tried a couple different belts from Autozone (Duralast brand) and they set up such shaking and vibration in the alternator I was worried it would break the mount. It was terrible. I ended up settling on the top quality belt from Napa and with that belt, the fit was better, and the alternator ran smoothly. Much less in the vibration department.

For my setup, I ended up with a 45 3/8" belt. A lot of swapping of belts and lunch hours stopping by Napa and Autozone to swap belts, but I think the effort was worth it.