View Full Version : Spitfire GM Alternator conversion on 80 Spit

Paul Slice
05-26-2005, 07:25 PM
I did a alternator conversion a couple of weeks ago when my Lucus unit started to smoke when I cranked her up, at least it happened in the garage not on the road. After searching the web I decided to go with a Internally regulated GM unit which is a 63 amp unit. I know that this is a old well known conversion but I thought that I would save anyone thinking about doing this a few trips to the auto parts store to get the correctly clocked alternator. Clock refers to the output position of the 2 pin connecter used in this conversion, you do not want the connecter comming out right by your engine block or at the top. After a couple trips to Advanced Auto and some baffeled salesmen (what kind of car is it for? a Triumph Spitfire sir. Is that a GM product? no sir its for a conversion, huh? )
Last night was the first time that I drove my 80 Spitfire at night since it was installed and I did not know that my headlights were that bright, like a modern car.The conversion is easy and looks ok and is much cheaper than the old lucus unit. I used a "J" alternator bracket from a mid 70s MGB that I got off of ebay for 7 dollars and used the origional fan belt.
Anyway here are the Advanced Auto part numbers and prices

P7127M-9 GM 63 AMP ALT. 34.94
5472830 2 pin connecter socket assy 2.98

If you do not have a advanced auto near you want a unit with a clock position at 9 oclock position, hense the -9 at the end of the part number. Tell them its from a 78 Camero with a 350 and no AC. Attached are some pictures of the finished product.

05-26-2005, 11:10 PM
Does the above information apply to the TR6 as well as the Spitfire?

Paul Slice
05-27-2005, 07:40 AM
do a google search for , tr6 gm alternator conversion, and you will get lots of info. looks like they use the same unit

05-27-2005, 10:12 AM
Just for your info, that number cited is basically an industry standard. It's the Lester numbering system that most electrical rebuilders use. The "P" was added by the rebuilder, and the "M" has metric threads instead of SAE, which would be listed as just a 7127-9.

05-27-2005, 10:22 AM
I did the GM conversion on my TR6 a couple of years ago and have had no regrets whatsoever. I remember having to do a little grinding on the alternator to get it all lined up and having to make another bracket. It wasn't too bad.

05-28-2005, 01:56 AM

Here's a photo of the same alternator installed on a TR4.

Here it's on the RH side of the engine, so the "clock" is at 3. It was decided to install this after a large electric cooling fan was installed, which also means a thin belt conversion and a harmonic balancer replacing the fan hub/extension.

The original generator was insufficient for the cooling fan, a total of 4 halogen lights up front and an electric fuel pump, along with everything else.

One consideration when upgrading: This alternator is rated at 60-63 amps, but tested to be producing 76 amps at 2000 rpm. This is 4x or 5x the output of the original generator. Time to upgrade some wiring, too, or risk frying it! Either a single heavier gauge lead or a parallel wire will be added to handle all that extra juice.

With TR4, there is also the conversion from positive ground to negative ground. And, the original amp meter in the dash is only +/- 30 amps, so will need some attention.

The external voltage stabilizer will no longer be needed.

Installation was pretty straight-forward. As previouisly noted, the bottom/front boss on the alternator needs to be trimmed a little to align the pulleys. In this case, 3/8" was sufficient. The adjustable bracket is the original item, straightened and attached to the rear of the top boss on the alternator. An approx. 4" long spacer was put in between the two generator mounting brackets on the bottom, allowing the use of a single, approx. 6" long x 3/8" bolt. There is also a bracket welded to the spacer to bolt up to the lower/rear mount of the alternator.

Wiring remains to be done, but there's other engine work in progress first.

One other thing, on TR4 (or 2/3/3A/4A) I'd strongly recommend a heat shield between the alternator and the exhaust manifold or headers. In this case, the headers you glimpse in the photo have since been "wrapped", so no heat shield was used.

My only disappointment is that the alternator is about the same weight and size as the original generator. No significant savings. Maybe next time a "racing mini-alternator" would be fun to try. Most offer 50 amps, but are much more expensive.

The #7127-3 alternator (rebuilt) cost $50, without a core exchange, here in San Jose. Incidentally, the auto parts store here didn't have a reference to that number, suprising considering how common this Delco is.



05-28-2005, 08:46 AM
Alan, what's with that funky exhaust flange stud sticking out of your header?


05-28-2005, 08:54 AM
Yes it is urprising how common the delco unit is.I have been using them on my sunbeams for so long I have forgotten since when.They are cheap and utmost reliable.I don't know how you rate them in yankee land but up in the great white north they rate them at 70 amps so not surprised to see your 73 amp rating.
/ubbthreads/images/graemlins/cool.gifand its sunny again

05-29-2005, 04:32 AM
Alan, what's with that funky exhaust flange stud sticking out of your header?


[/ QUOTE ]

Hi Bill,

That's a universal replacement stud I picked up at a local auto parts store. There was just an old bolt in there ever since I bought the car in 1977. But, the new headers have a thicker flange and the old bolt wasn't long enough, so I "upgraded". Since the photo was taken I've painted it black so it's less obvious.