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because carbon isn’t really that good a conductor. If it’s an open circuit (infinite ohms), you didn’t get that spring
seated against the electrode; pull it apart and try again.
While the spring stretch might render the cheap aftermarket cap workable, there is a far better fix: making sure the hole
for the brush features a metal sleeve rather than simply being a hole in the plastic. Thus, the spring will make a good
contact with the terminal whether it reaches the bottom of the hole or not; the wide portion contacting the sides of the
hole serve as electrical contact. It also protects the plastic from heat, wear, etc. And the spring seems to be easier to
install properly, since the wide portion is sliding on smooth machined metal rather than molded plastic.
This is an easy fix on the part of the manufacturers; they merely have to redesign the aluminum terminal to include a
sleeve that extends all the way to the inside surface of the cap. And, believe it or not, they have made this fix. Andy
Klopfenstein reports that “Apparently the manufacturer discovered the apparent flaw we have seen in the cap. This
new cap has a different inner aluminum cross section. The new inner aluminum shank now comes all the way to the
bottom of the center post (inside cap). You can see it when you look at the contact button. The contact button now
slides up and down in the aluminum shank.” Hey, even the aftermarket caps aren’t cheap; since you’re spending good
money, make sure you can see aluminum around the carbon brush within the cap as Klopfenstein describes before
paying for a new cap.
If you are unable to find an upgraded cap or have a relatively new pre-upgrade cap and don’t wanna throw it away just
yet, the following fix to the pre-upgrade aftermarket cap is easy: Remove the carbon brush and spring. Fit a 9/32” bit
into the drill, preferably a variable-speed critter so it can be run slowly. A drill press might also be helpful here. Drill
right down the center hole inside the cap until you get to aluminum. Keep drilling until you are drilling the bottom of
the hole, not just the sides. Then take a piece of 1/4” ID brass tubing (available at better hobby shops) and bevel one
end’s OD edge with a file. Poke this end into the hole, set the cap down on a firm surface, and tap the other end of the
tube with a hammer until it seats securely in the bottom of the hole. If it fits tight, great; if it fits too loosely, pull it back
out and apply a little JB Weld around the outside of the tube about 1/2” from the end (not at the very end!) so that it is
smeared into the edge of the plastic as the tube is driven home. Let it dry. Then, using a Dremel with a cutoff wheel in
it, cut the tubing off flush with the surface of the plastic. Clean up the edges a bit, then reinstall the spring and brush.
Regardless of what type cap you end up with -- even a genuine Marelli -- it wouldn’t hurt to stretch the spring as
described above, just in case.
THAT’S NOT ALL: George Schulte says, “I came out of a store after 15 min of shopping to see smoke billowing out
of my hood. When I opened it the flames were pretty well involved. Luckily a fire extinguisher was close at hand.
The fire began from the center of the distributor cap. The lighter cap besides being cheaper and lighter is also
flammable. I noticed some arcing around the center hi voltage lead but didn't think too much at the time because the car
was running fine. The plastic is not hi temp and the entire cap caught fire which spread to the rest of the wires in the
area which spread out and melted the fuel hoses.”
REPLACING THE DISTRIBUTOR: Perhaps the easiest and cheapest way to avoid the problems with the Marelli cap
and rotor is to replace the entire Marelli distributor while keeping the rest of the Marelli ignition system, which has no
significant problems. Any 12-cylinder distributor (or even two 6-cylinder distributors, if you can figure out how to
mount them) will take the spark from a coil and distribute it to 12 cylinders; you’re not worried about timing advance
curves because the Marelli electronics will still be handing that.
The distributor of choice is obvious: the Lucas distributor! It’ll bolt right in.
There is one problem, however: connecting the outputs of two separate ignition coils to the single center post on the
Lucas distributor cap. You can’t just splice them together; a spark generated in one coil would backfeed into the other
coil rather than jumping the gap at a spark plug. Charlie Welkie points out that there’s a product on the market for this
job: an MSD Automatic Coil Selector, part number 8210. It’s a diode pack with two inlets and one outlet for
connecting two ignition systems to one distributor cap. Its original intention is to allow racers to install main and
backup ignition systems in their race cars, and when the main one fails simply switch on the backup system and keep