Lucas to GM/Delco Alternator Swap
Modifications to the Alternator
The body of the Delco alternator has it's two mounting ears (flanges) directly opposing each other at 12 and 6 o'clock . The Lucas unit has them at roughly 1 and 5 o'clock. Both ears on the Lucas unit are the same thickness. The Delco has one ear approximately the same thickness as the Lucas unit, but the other is nearly 2.25" - 2.5" thick. One small flange on both units is threaded, designed to be the flange that meets the lower adjustable mounting arm. The Lucas unit has a second flange at 12 o'clock on the back of the unit (electrical wiring end).
Lucas top view Delco
The Lucas unit has two mount ears on top. The Delco only one really wide one on top. The Delco is larger in diameter, but also shorter, front to rear.
Lucas Pulley view Delco
The flanges are in different positions. In this photo, the wide flange of the Delco is at the top of the picture. The Lucas still has the original lower adjusting bar attached. You'll also notice the pulleys are very close to the same size.
Lucas back view Delco
The Delco uses a two conductor electrical connector for the 'sense' and 'indicator' lines. the main battery connection bolts down to a large stud on the back. (dark circle with silver center at 2 o'clock on the Delco unit)
BGT PROBLEM 1: When first trial fitting the Delco unit, I realized there was no way the wide flange on the Delco unit was going to mate up to the stock mount flange on the engine. It would have put the alternator way too far forward or way to far back to have the fan belt pulleys line up correctly. At first I seriously considered cutting a slot into this wide flange that would allow the flange to sit fore and aft of the engine mount ear. But I figured if I did that I'd have to do it on any future possible replacements, and it would be hard to fine tune the position (depending on my marking and cutting accuracy's) I didn't want to mess up a good alternator if I didn't cut it right so....
BGT SOLUTION 1: I simply inverted the Delco. Small flange at the top, large at the bottom. I worried this may not be strong enough as the Delco is a bit heavier than the Lucas unit is. But as you'll see, that really isn't a problem.
BGT PROBLEM 2: The two terminal connector was now pointed directly at the engine block up under the upper mount.
BGT SOLUTION 2: The four bolts that hold the halves of the Delco together can be removed, and with care, the halves can be separated and rotated to any direction you want the electrical connector to point.
Note: Before re-assembly you must pre-position the
brushes or you'll destroy them trying to put it back together.
Which is simple. On the back of the alternator, is a little hole through the metal case, about 1/4"-3/4" out from the center bearing. This lines up, inside with the 'tops' of the little slots the brushes ride in. Push a straightened out paper clip (a finishing nail is a bit short) through the hole in the back...just up to the back of the rear slot. After pushing first, the rear brush and spring down, push the paper clip in and through the holes in the top of the slot to 'capture' the brush in place. Now push down the front brush, and push the paperclip in a little further to capture the front brush.
Now you can safely assemble to body halves in any of four 'rotational' directions you want. After bolting it together simply remove the paperclip from the hole to release the brushes back out against the stator.
BGT Since the small ear on the Delco is threaded, I drilled it out to clearance the original Lucas unit upper mount bolt.
on a BGT for 'proper' fit
BGT Now to get the pulleys to line up just right, I felt it necessary to remove a little of the lip that is on the back side (engine flange side of the mount ear) of the mount ear to move the alternator back about 1/16". Simply file off the lip flush with the rest of the flange surface. I used a Dremel tool and sanding drum. A hand file or a hand drill and grinding stone would work equally as well. You may not really need to do this, but my 'eyeball' measurement techniques and my general mechanical attitudes, prompted me to 'go the extra mile'.
Spitfire Nothing on the alternator had to modified. I did make up a small metal tube as a spacer to fill the larger flange hole. I used a piece of soft metal designed for body panel repair and simply used pliers to wrap it around the bolt as a mandrel for shaping. I then stuffed it into the wide flange hole so now both mount hole in the wide flange is the same size as the original spitfire engine mounted flange hole.
homemade 'filler' tube before installation in the wide
flange hole, and the new lower mount bolt used.
Believe it or not, the wide flange on the Delco alternator is the exact same width (to within +/- 0.5 mm) as the Lucas unit flange plus the length of the stock Lucas to Spitfire mounting spacer tube (green arrow) used on the lower mount. At least on my 1975 Spitfire. ymmv!
Bolting it up to the original lower mount, puts it in near perfect position for fan belt alignment.
73 MG Midget
The Midget installation was as clean as the Spitfire installation. This I believe was simply due to the variation in the Lucas alternator pulley position as compared with the BGT installation and it's original Lucas alternator. I used the same 'J' bracket as on the MGB installation for the lower mount. And as with the others, a tube was inserted to make up the diameter of the lower bolt mount of the GM/Delco alternator. The original Midget alternator adjustment bracket was used as the rear upper mount of the GM/Delco unit. (see the green arrow)
GT6 Nothing on the alternator had to modified. I Actually used a spring, as the 'filler' for the 'fat hole' for the wide mount flange of the Delco unit. This way the bolt diameter matches the GT6's original alternator lower mount arm hole size.
I inverts the mount, using a long bolt through the wide flange. I added two oversized nuts as spacers, before the bolt passes through the home made rear mount tang (B and C in the pics above). The original Lucas upper mount bar was used as the new lower mount. (D in pics above) and runs from the lower outer front plate bolt to the lower ear of the Delco alternator. For my setup, a 43" fan belt (already on the car when I bought it) worked for me, but was just a bit loose for my liking. Since since a 42" belt was too short, I found a 1085mm metric belt was perfect. I had to hook the fan belt over the pulley before mounting the upper long bolt, as the pulley groove depth is about all the adjustment distance I had (groove width in the original mount arm now underneath). You can scan the Spitfire installation for the wiring, as it's identical for both the Spitfire and GT6.
The "J" bracket