Tiger Alternator Conversion
 
Motivation
I had planned to do an alternator conversion somewhere along the line but the decision to do it now rather than later was spurred on by the seizing of the generator's rear bearing. This bearing is a light press fit in the rear pressed-steel generator housing, and when it seized it quickly wore a groove in the rear housing, which made the housing unusable.
An alternator has several advantages over a generator. Generators are less reliable partly because the current is generated in the rotor, which is then drawn from the windings through a commutator and a brush pair The many segments of the commutator (required to give DC output) are subject to wear and shorting out. By contrast, the alternator generates an AC current in the stator (the non-rotating windings), which is rectified (turned into DC) using six diodes. The rotor is used to create the 'field magnetization' which causes the AC current to be generated in the stator when the rotor is spun. For this purpose, the rotor only needs to have two continuous conductive bands (called 'slip rings') to conduct the field current from the brushes to the rotor. Because the slip rings are continuous they do not wear the brushes as dramatically as do the commutators in the generator, nor is there the possibility of creating a short between segments. Alternators are more compact than generators of equivalent capacity; a typical modern 90 or 100 amp alternator is little larger than the Tiger's generator, which is rated at 35 amps.
An additional advantage to converting to an alternator is that a modern, internally regulated alternator can be used, which simplifies the wiring and eliminates a common source of charging system failure.

Component Selection
There are a number of alternators suitable for use on a Tiger. The biggest problem is that it is necessary to mount the thing such that the belt pulley lines up with the Tiger's water pump and crank pulleys. Because the Tiger used a non-standard water pump and crank pulley, it is going to be difficult to find a Ford bracket that will fit the Tiger. Since this is the case, it is not really necessary to use a Ford alternator at all, and in fact several Tiger owners have fitted a Chevrolet 45 amp 'one-wire' alternator. In my case I had an internal-regulator Toyota alternator sitting on a shelf, and I have used these alternators successfully on a number of street and race vehicles, so I decided to use it. The Toyota part number is 27060-28020, and they can be found on 1980-1982 Corollas powered by the 1800 cc 3T-C engine. The belt tension adjuster brace is Ford part number C90E-10145-B.

Fabrication
I had to make a bracket to mount the thing, of course. The alternator mounts using a 10mm by about 5 inches long bolt that goes through two ears on the alternator, and I had a friend machine up a piece of 1" cold rolled steel bar stock to fit between the ears. The rearmost ear has a pressed-in distance piece that allows for slight variation in length so this is easy. I used a piece of 3/8" steel plate for the cylinder head side of the bracket. Cut it to a kidney shape, drilled two 3/8" and a 7/16" hole and bolted it to the head. The left arrow in the picture at left points to the lower (7/16") bolt in the head mounting plate.

At this point I threw everything in the car and eyeballed the alignment of things. By sheer luck the rearmost edge of the alternator ear bracket (the 1" bar stock piece) lined up with the front surface of the head plate. I then measured the distances from the two 3/8" holes to the bar stock piece, and this gave me enough information to build the stuff inbetween.

I used three ribs of 1/8" steel plate for the stuff inbetween. I cut out the middle rib (right arrow in the picture above) and welded this to the 1" bar stock, then welded that to the head plate. I spent a few minutes after that with a large square to ensure that things were straight, then tacked the other two ribs into place. Recheck the squareness again and adjust as necessary. At this point I took stuff home again and bolted the bracket to the head and the alternator to make sure that the alignment and measurements were okay. As can be seen from the picture at right, the dipstick tube was a very close fit and required both a cutout in the middle and upper ribs, as well as bending the dipstick tube. The ribs were then boxed in front and rear with more 1/8" plate to ensure a rigid structure. After that, I cleaned things up with a wire wheel in the bench grinder, and painted it.
 
 

Wiring
For the wiring, I decided to use the existing harness as much as possible; since I had to remove the regulator anyway, I used the large brown/yellow wire that ran from the generator to the regulator, and connected it to the large brown wires at the regulator side, and to the battery terminal lug on the alternator. The small brown/yellow wire on the regulator connects to the dash charge light; I connected this to the brown/green wire that ran to the generator, then on the generator end I connected it to the "light" spade terminal. I had to run a new wire from the ignition terminals at the fuse block (white wires) to the "IG" terminal on the alternator. This wire is just barely visible (I used a black wire and ran it along the firewall) in the picture. Feel free to bug me at SUNI if I haven't wired the ignition lead better yet.

The belt I used was a few inches shorter than stock. Use your favorite brand.


Back to Theo's Tiger Page