|Archive Index | Current Issue|
Here's an easy upgrade that replaces your distributor's points and condensor with an optically controlled electronic unit. Once installed, the system is essentially maintenance-free -- the major benefit of the XR700. Crane also offers a more expensive and complicated high-performance version, the XR3000, which uses a computer chip to control coil current and dwell.
Points require regular replacement as their contacts "burn" and as the fiber surface that contacts the distributor rotor cam wears down. Both factors cause the timing to vary over the course of the points' service life. Condensors rarely fail, but when they do degrade, it's a tough thing to troubleshoot -- we once had one that permitted the car to start right up and idle properly, but it simply would not run over 2500 RPM. It took us several days of head scratching, messing with fuel pumps and filters and digging into carburetors before we figured out that the condensor was at fault.
The heart of the Crane system is the optical trigger, consisting of an LED (Light Emitting Diode) and an opposing photo diode, mounted on the breaker plate in the distributor. Attached to the distributor's rotating shaft is a chopper disk -- a thin black plastic disk with four radial slot in it -- which passes between the LED and the photo diode. The LED is lit whenever the ignition is switched on, but light from it only hits the photo diode when a slot goes by. The photo diode then produces a pulse which is amplified by an "ignition module" and passed to the coil.
There is no mechanical contact between the fixed and rotating parts and, consequently, no wear. Set the timing once and forget about it. This system does retain the original distributor cap and rotor; those, of course, are still subject to wear and occasional replacement, but this will not change the timing.
The ignition module attaches anywhere under the hood with two sheet metal screws. It's a good idea to locate it away from heat and in a dry place. We picked the angled plane just below the top of the pedal well on our 122S, which is conveniently close to the coil. There's enough length of wire to permit putting it just about anywhere you like.
A four-pin Molex plug connects the ignition module to the trigger. While the pins come pre-crimped onto the trigger unit's wires, they must first be routed through the hole in the distributor body that used to house the points - condensor - coil connection, and then inserted into the plug body, where they lock into place. Once this is accomplished, you can seal the hole with RTV or the caulking of your choice to keep moisture and dust out of the distributor.
Supplied with the kit is a little metal rod that is infernally easy to lose (yes, we did eventually find it again). This is a pin extractor -- without it, you'll never get the pins back out of the connector body, and you'll never get the trigger assembly out of the distributor with the connector in place. Attach a big masking tape tag to the extractor and keep it in your car's toolbox. That way, you can swap the unit into another distributor if you like, or, should the unit ever fail on the road, you can easily reinstall the points and condensor. You have been warned.
If your car has the armored cable between the ignition switch and the coil positive terminal, you have two choices. 1) somehow cut into the cable, or 2) mount a new coil. [New info: Method 3] We opted for the latter option -- a standard Bosch "blue" coil works just fine, or you can use a high-performance bejillion volt model. One caveat: the system requires a ballast resistor to prevent damage to the ignition module -- the Bosch coil has one built in, but you may have to wire up an external ballast depending on your choice of coil.
Fortunately, the armored variety of ignition switch has a switched terminal external to the armor (the one that doesn't go to the starter solenoid), and you can easily run a wire from there to your new coil.
On P1800s with the Smiths current-sensing tachometer, the XR700 system can overload the tach and cause erratic reading. This is easily corrected by taking the loop out of the sensor on the back of the tach and rnning the wire straight through it. The instructions cover recalibrating this sort of tach if you need to following this procedure.
The XR700 is readily available at many auto parts stores. Prices vary quite a bit, but you should be able to buy one for around $100. The system is C.A.R.B. approved and should be legal for use in all fifty states (other conversions, even the elegant Mallory, are not).
You may want to know that there is a way to install [the XR700] without cutting into the armored cable or replacing the coil, which is as follows:
Obtain two diodes with value 1N4007 (I obtained them from Radio Shack), cost about a buck for both.
Solder suitable wire onto each diode lead, so you've got two lengths of wire with a diode soldered in the middle. Use pliers as a heat sink to prevent damage to the diodes.
Connect one diode wire to the solenoid on the starter motor (12 V with Key In "Start" position); the silver ring painted on the diode should be farthest from the starter.
Connect the other diode wire to a 12-V source (12 V when key is in the "on" position), again with the silver ring pointing away from the source.
Attach both of the free diode wires to the red wire from the XR700 box. I would recommend supporting the diodes with a rigid casing (for me, electrical tape wrapped around a plastic stick) as the leads are fragile.
The yellow wire from the XR700 box is now attached to the white wire from the tach; the red wire from the tach is attached to the (-) and only post on the coil (Note: both my tach wires were white, so it took some experimenting to figure out which way they were supposed to go).
Everything else is the same as in the XR700 instructions. It worked like a charm. The only big snag I hit was that the distributor static shield had to be cut to allow the distributor to be reassembled correctly -- something they didn't mention in the book.
I received the above instructions from Allison [the former manufacturer], and they apparently originated with IPD (who apparently used to sell the XR700 plus the diodes in a special kit). It was a fairly simple way to avoid coil replacement and/or cutting the armored cable.