View Full Version : TR4/4A 4A Generator Conversion

05-01-2006, 06:05 PM
Greetings to All. I have been a "looky lou" on this forum for some time and have gathered much valuable information concerning my '67 TR4A. My current project is converting from the generator to the Delco 7127-3 alternator. I have modified the generator pulley to fit the Delco unit instead of trying to convert all of the pulleys to the thin belt. Many of you who have made this conversion, state that you were able to use the original 3/4" wide belt. My problem is I can't get the wide belt to fit onto all 3 pulleys. If it did fit, I don't believe there would be any slack for adjustment. I have ground down the front generator mounting plate plus ground down the lower mounting bracket, on the generator casing plus one little nodule on the alternator casing. The alternator now moves all of the way against the engine block so there is no more I can do there. I have tried the non-original belt w/cogs, from Moss, plus the original belt w/o cogs from TRF. There is no way that belt is going to slip onto all 3 pulleys. I must be missing something here. Some devine guidance would be greatly appreciated. Thanks /ubbthreads/images/graemlins/frown.gif <font color="black"> </font>

05-01-2006, 07:15 PM

Geez, wish I could be more help, but I did a thin belt conversion on my TR4 at the same time I installed the Delco 7127-3 (and included changing to an aluminum pulley at the water pump and a harmonic dampener/pulley at the crankshaft). The thin-belt setup also doesn't have much slack and the belt can be a bit of a struggle to get on. But once it's seated in all three pulleys there *is* a little bit of adjustment. I figure the belt will stretch some, too, so planned to use this set up for a while, although installation of a new belt is a bit tough.

Let me throw out a couple ideas:

1. I reused the upper generator mounting arm, after straightening it to best align all the pulleys. That arm needed a bit of grinding on the bottom edge where it rubbed against the alternator case and kept it from moving freely all along the adjustment slot. Initially, the interference with the case of the alternator prevented slackening enough to install the belt. Also, I bolted the upper arm to the back side of the mounting lug on the top of the alternator, not the front where it fits on many cars.

2. Perhaps trying to reuse the original generator pulley is the issue. I don't know if it is a larger diameter than what's normally used on the alternator. And, I can't compare them for you right now since the original generator and its pulley are packed away in storage.

I can give you a quick measurement of the thin-belt pulley on the 7127-3 that's installed on my car, and that might help you check if the pulley size is close to correct. It is 2-3/4" in diameter, at the flange, i.e. not accounting for the v-groove machined into it in which the belt fits. The thin belt stands out of the v-groove by only about 1/16" approx. If it were even just a little larger diameter, a thin belt the length I've got installed (925mm, if I recall correctly) wouldn't fit either.

Someone makes alternator conversion pulleys to suit the Delco with the original 3/4" wide belt. You might check into one of those and see if it is a smaller diameter and might resolve the problem.

Note: a smaller diameter pulley will make the alternator spin a bit faster in relation to engine rpm. That's probably okay for regular street driving at modest rpms. But the opposite - an under-driven alternator with a larger pulley - is often used if the car is commonly driven at higher rpms. One reason I converted to a thin belt is to better allow the option of going a larger alternator pulley/longer belt. Thin belts come in a wide variety of lengths. A change like this is simply not possible with the TR's original wide belt which are pretty hard to find at all, let alone in various lengths.

Hope this helps!


05-02-2006, 06:19 AM
Take a 3/8 or (a close approx of your belt width) piece of rope around the 3 pulleys with the alt in the lowest position (but not touching the block!) and at its tightest position getting measurements of both. With that info and your old belt, go to your favorite parts store and get a belt that will fit. Don't forget to write down the size of the new belt in a few places so you will have it available for replacement.

05-02-2006, 12:29 PM
Red, Vette's idea works. I did a conversion similiar to yours and Napa had a belt that worked. I'm not at home, however tomorrow I'll find the part number and pass it along.

05-03-2006, 10:09 PM
The belt that worked for me was a NAPA # 28400. Hope this helps.

05-04-2006, 02:25 PM
Red Romper here... Thank you Lads for all of the information. I went to the NAPA store today inquiring about the NAPA #28400. They did not recommend using this belt, for my application because this belt is 7/8" wide. They felt it would ride too high in the pulleys plus the pulling power strength for the belt is in the upper portion. Bob, I would assume seeing how you have been using this belt, for some time, that this hasn't been a problem for you? I have found a belt that will work but have been holding off, waiting to see if there was a better option. I found this belt, CarQuest 6938, on this forum, in a thread that had a link to a vendor who sold conversion kits on Ebay. There was a photo, of the kit, which included the belt number. Problem is, that this belt is not an automotive belt but a lawn equipment belt. The regular duty belt comes in black but the heavy duty belt is green. I have tried the green belt on and it fits nicely. It is 5/8" wide so it sits down into the pulleys a bit but does not bottom out on the pulleys. Is the World going to laugh at me for having a green fan belt? I have seen green cooling system hoses for LBC's so maybe not. Has anyone experienced any issues with the NAPA 28400 with the original 3/4" wide pulley(s) application?

05-04-2006, 03:04 PM
Red, I've used that belt for five years now, I average about 3000 miles per year.

05-04-2006, 05:20 PM
Red Romper here......Thank You Bob. I am going to go ahead a try the NAPA 28400 belt. I'm really not crazy about running on a green lawn mower belt. My gosh, people would laugh at me....oh well, they'll find another reason. Have a great day....!

05-04-2006, 08:01 PM
I can't wait to get a green belt on my TR6! It will match up with the plug wires and hoses.Other than intended use and color, how does it vary from a stock belt (length, width)?

05-04-2006, 09:37 PM
Vettedog72, Red Romper here......the green belt is NAPA # 5L380W. I was told that this is a universal part # so you can get it just about any parts store. It is
5/8" wide, 38" in length. I don't know how this compares to a TR6 belt. I was told that it is not that unusual for a rodder, etc: to use this belt in a custom application.

05-06-2006, 11:23 PM
Update: NAPA fan belt 28400 fits very nice, very nice indeed. I don't understand how some Lads said they used the original belt with their generator/alternator conversion. In my experience, there was no way it was going to fit onto all 3 pulleys. Maybe they were referring to the originial "width" of 3/4". Much thanks for all of the help and suggestions.