I have an Allison ignition system on my '74 Jensen Healy, and know a little
bit about them. They are a "breakerless" ignition system that replaces the
function of the points and condensor in the standard system. The allison system
uses an LED and Photo sensitive device (photo diode?) , and a slotted disk
that fits on the distributor shaft that breaks the beam. These parts are
all mounted inside the distributor where the points used to be. There is
also a "black box" which is mounted on the firewall which provides power to
the LED, senses the output of the photo device, and drives the - side of
the coil. I can't say exactly how they work, since I don't have schematics.
As far as advantages over the original, there are several: 1) since the
points are gone, you don't have to replace or adjust them ever again, in
fact I haven't had the top off my distributor in over 3 years!. 2) Moisture
does not affect the ignition system, so the car starts better in cold/wet
conditions than orginally. 3) The spark is stronger and its shape is
controlled, so plugs get replaced only every 30k miles, and are gapped at
35-40 thou instead of the narrrower stock gap. These are the reasons that
electronic ignition systems are now standard on almost every new car.
As for disadvantages, there are some: 1) It is not original, so my local
Jensen dealer won't do warranty repairs :-). 2) On my car, the Tachometer
now reads about 20% higher than it did with the points. I don't know why,
and I haven't put a scope on to see. I'm afraid to tear apart my Smiths
tacho since they aren't easy to replace. 3) It is more complex than the
original, which makes troubleshooting difficult. 4) Since the sparks
are stronger, the distributor cap must be perfectly clean to avoid
carbon tracking on the inside.
I think the advantages outweigh the disadvantages and continue to
to use the system. On the Lotus engine, changing and adjusting the
points was a pain, so I tried the Allison with good results.
bob@novell.com
carbon tracks.
>
>
>
> SOL Crowd,
>
> My Spitfire came with an Allison ignition system conversion.
> In fact it came with it installed improperly - the rotor fitting with
> the slots was for a 6 cylindar (6 firing signals) and the ballast
> system and resistor were still connected - a "pro" mechanic found this
> nasty little secret out for me when I couldn't tune it to spec.
> Beleive it or not the car still ran, although poorly, I thought it
> just needed a tune up and plugs and thus ran poorly, I knew it did
> suffer from preignition because one of the plugs tips had burned
> completely off. Anyways the prev owner had obviously given up on it
> and that is why I got it so cheap.
>
> But to the question: I am afraid I don't really understand how
> these boxes work. There is a power lead, a lead to the coil, a lead to
> the distributer (presumably LED) fixture, and a ground. How does the
> vacuum advance play in this system? Basically I am interested to find
> out how these things work and why they are better than the old system.
>
> The mechanic that found the blunder and fixed it for me told
> me that the other system is a "pain in the a*s, and I am far better
> off with this refit". Well I thought maybe this is would be of list
> interest then.
>
>
> BTW I got my TRF catalogue today with some parts I ordered
> after I finally got through by phone. These guys are real asset.
>
> Kristian
>
>
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