I had offered earlier to post this and never got around to it -- my
apologies. My conscience was nudged by some recent posts on a similar
topic.
When Miss Molly, the '79 Midget from Hell, was in the process of being
rebuilt early this summer, I ran into some difficulties with the Lucas
alternator (ok, I got mad at it, boxed it up, and put it away before I
put it through a wall). Being much more comfortable with the GM
(AC-Delco) alternator, I grabbed one out of my pile o' parts, scrounged
up a couple of thingies, and presto! a working, reliable, alternator.
This was an internally regulated alternator, so the swap was pain-free.
The only changes I had to make were to the upper adjusting bracket, and
to the wiring harness plug-in.
The alternators are very similar in size and the locations of the
adjusting bolt and pivot bolt are also similar to their placement on the
Lucas unit. You would want to ensure that the replacement alternator is
'clocked' correctly, that is, that the plug in for the harness is located
to the right as you view the alternator from the front with the adjusting
bolt at twelve o'clock.
I used the stock location for the bottom bolt, but had to purchase a
longer bolt that fit all the way through both pieces so that I could
separately nut them. Use a couple of flat washers to distribute the
load.
For the top bracket I used an alternator bracket from an early 60's
Chevy: Cut off several inches from the end (I'd tell you how many, but I
don't have Miss Molly here to measure from, and didn't take notes when I
did it so you have to do some fitting) away from the curved end. The
stock location of the bracket did not work for me, so I used the bottom
bolt and right bolt (viewed from the front of the engine) on the water
pump housing as mounting points for the new bracket. You'll need a
couple of spacers to set the bracket out from the engine, and will need
to get longer bolts as well. I used a couple of 7/16" id chrome lug nuts
and some washers to space it approximately 1/2" from the housing.
Before you cut the bracket and drill the holes you need to carefully
measure amount of height you have available; check this from a known
point on the engine to the top of the stock upper bracket. Do not exceed
this height.
'Mock' the alternator into place by using only the lower bracket. It
should line up perfectly with the pulleys but check with a staightedge,
and adjust as necessary with shims/washers. You can now begin to trial
fit the upper bracket. Once you know where your bolt holes need to be,
drill them, making sure that the top of the bracket does not exceed the
maximum height you have available.
An easy method of checking for clearance is to clamp a piece of wood to
the engine so that the upper edge is at the height measurement that you
determined your upper limit to be. Place a piece of child's modeling
clay on the end of the wood. Slowly lower the bonnet. If the clay is
dimpled by the bonnet, you know that you have clearance equal to the
thickness of the clay between the dimpled area and the wood. You can add
more clay if the bonnet did not touch the clay.
Once everything is bolted together, all you need to do is change the
harness plug-in. Cut it off about two inches behind the factory plug so
that it can be reused if ever you need or desire to. There should be
three wires running to the factory plug-in: a thick brown wire
(approximately 8-10 gauge), a thinner brown wire (approximately 12-14
gauge), and a brown/yellow wire (approximately 14-16 gauge).
Pick up a new GM plug-in by either going to the junk-yard and cutting
several free (extras are never a bad idea), or by purchasing one from the
parts store. There's a company that makes 'Help' items that generally
has a display in most stores; these are those little things that are a
pain in the tuckus to find, but always seem to break. I used a GM
alternator plug-in extension from this company as a source for my new
plug-in. There are only two wires on the new plug in.
The biggest wire (brown) in the loom feeds the battery so it will be
connected to the terminal on the back of the alternator. Use a ring
terminal of appropriate size; I recommend soldering it to the wire and
heat shrink tubing to protect it.
The remaining two wires will be dealt with in the following manner: You
will notice that the plug-in position on the alternator is marked '1' and
'2'; these correspond to the position on the plug-in. Right now I don't
have Miss Molly here so I am working from memory; I strongly urge you to
double check me. I will be visiting her this weekend so will double
check then and post any corrections.
'1' should be a red wire on the new plug-in. This will go to the battery
position on the solenoid and needs to spliced to the smaller brown wire.
'2' should be a black or gray wire on the new-plug in. This will go to
your indicator light and needs to spliced to the brown/yellow wire.
Again, I recommend soldering and insulating with heat shrink. Basically,
all you need to do is put the thickest wire (brown, the battery feed) on
the post of the back of the alternator, the next thickest wire (brown,
the ignition feed) on the thickest wire on the new plug-in which should
be '1' above, and the remaining wire (brown/yellow, the indicator light)
on the remaining wire on the new plug-in which should be '2' above.
I believe this would also work on any similiar MG three wire fed
alternator without a lot of jacking around. Also somewhere around here,
I have the schematics to convert an externally regulated system to
internally regulated. If I can find it, I'll post the directions.
Luck,
Rich
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