View Full Version : TR4/4A TR4A generator to alternator conversion

05-29-2005, 10:00 PM
I'd like to convert to an alternator on my TR4A. I've seen lots of talk about this conversion for a spitfire but not for the TR. Apparently, the pulley that comes with the good Delco alternator is too narrow... and the pulley shaft hole from the generator is too large for the Delco alternator shaft. Sounds like some machining. Has anyone done this?

Geo Hahn
05-29-2005, 10:20 PM
A message from another list, another time, that I archived... note that the referenced VTR pages are now restricted (members only) though they may be available using the 'wayback machine':

==== from another TR enthusiast ========

I just completed the alternator conversion on the TR4, and I though I'd share some lessons learned with the list. My goal was installing a Delco 10SI alternator in a way that would appear as original as possible.

The instructions on the VTR site were my core reference, with additional tidbits from various web sites. The VTR instructions were very helpful, but the following details were either missing or could use some clarification:

- I found a suitable pulley at Quick Start Automotive Electric Products for about $20.

- Modifying the mounting boss on the Delco alternator was very straightforward. Trimming the boss down to a thickness of 1.75" gave perfect alignment with the water pump and crank pulleys without needing any shims.

- The wide pulley takes up more of the alternator shaft than the narrow pulley that came with the alternator. The basic 10SI (7127) alternators are apparently all alike, but there are different fan designs. The alternator I bought had a fan that was domed in the center with a thick spacer under it, leaving very few threads for the thin attaching nut. The wide pulley covered all of the threads at the end of the shaft, making it impossible to attach the nut. I swapped the old fan and spacer from a core unit for the new fan, and solved the problem. Its difficult to describe, so just be sure to get the pulley first and make sure it will fit on the new alternator before you buy it.

- I found it impossible to install the recommended 7" bolt through the front and back "ears" of the generator mounting bracket. The cross-brace is in the way in the front, and the exhaust manifold interferes in the rear. Instead, I used a 3/8" x 3" bolt through the alternator and the front
generator mounting hole. BTW, the hole in the front of the generator mounting bracket is 1/2" diameter, while the mounting hole in the alternator is 3/8". I didn't want any wobble here, and installed a bushing to take up the slack and provide a very solid mounting.

- The original fan belt would not fit over the pulley, so I tried longer belts, up to 40" (NAPA TR28400). The longer belts allowed the alternator to sit too close to the fender wall for my comfort. Grinding down the edge of the generator mounting plate and front engine plate where the alternator was touching them allowed the alternator to swing closer to the block and provided enough room to use the original fan belt. The alternator seems to sit just right.

- I used an old control box as a terminal block, following the general instructions provided in https://www.vtr.org/maintain/alternator/gm-tr4a1.html. Rather than installing a fusible link, I'm planning to install a circuit breaker inside the box to protect the wiring harness against the 60+ amp surge that the alternator is capable of producing with a dead battery.

It took considerably more than 2-3 hours, but it works fine and you'd have to look pretty carefully to tell that its not an original installation.

Geo Hahn
05-29-2005, 10:28 PM
P.S. These may be the archives of the referenced links...