I had always admired John Titus's ignition conversion using GM HEI components but being very frugal and owning two SM's I always hoped another alternative would present itself. When I learned that Pertronix had developed a conversion for the early GM (non HEI) odd fire V6 engines I knew there would be a way.

The Pertronix kit #1165 (about $65 from Retro Rockets, P.O. Box 200, Norfolk, Ct. 06058) consists of a 3 inch ring carrying the trigger magnets alternately spaced at 45 and 75 degrees (odd fire) and a hall effect sensor that simply attaches to one existing coil.

By using a Mopar 6 cylinder distributor cap NAPA MO40SB and a Mopar rotor NAPA MO13 very little is left to complete the conversion. This rotor needs to have a new tip fashioned that has an arc length equal to one half of the distance between the contacts on the distributor cap to accomplish the heel and toe firing needed in a single tipped rotor odd fire application. Simply remove the rivet from the rotor, grind a new tip (I used an old sabre saw blade for raw material) and reuse the threaded rivet to reassemble. You will need to match the shape of the old tip and drill a hole for the rivet. You will need a pair of 5 x .8 x 30 metric screws and two home made metal tabs to act as clamps for the distributor cap. Remember, the tip is not centered on the distributor cap contacts when it fires on an odd fire engine. #1 fires off the trailing edge of the tip and then #6 fires off of the leading edge of the tip and so on and so on. You should mark the #1 wire on the cap with white out (It will be the one immediately preceeding the mounting hole ccw).

A 3 inch circular piece of rigid plastic or fiber glass is needed to mount the magnetic ring on. I used a square pvc cover plate from an electrical conduit junction box (regular plastic electrical boxes are too fragile) and used an adjustable hole cutter mounted in a drill press to cut a 3 inch circle from it. The raised printing on one side of the plastic was enough to throw the magnet ring out of level. Use a straight pin to locate the magnets and mark them on the edge of the ring with white-out (you won't be able to locate them once they are in the distributor otherwise). Also transfer the firing point of the sensor's yellow dot to the front of the sensor with white-out.

Using a rigid 3/4 inch electrical conduit compression fitting, remove the compression nut and collet. Fashion a bushing (I used a bronze sleeve bearing). It will have to be turned down to approximately 1 1/16 inch to fit into the compression fitting. By choosing the bushing carefully or by sleeving the inside you can match the diameter of the Mopar rotor. The bushing should match the length of the rotor base and the bottom of the rotor should match the bottom of the bushing. The rotor has a "plastic guide" inside that will fit into the small notch of the SM distributor shaft. Forcing the rotor down on the shaft will resize the "plastic guide" (which is slightly oversized) to match the notch. Test the rotor assembly carefully to make sure the rotor and the bushing are fully seated in the compression fitting. Drill a small pilot hole through the adaptor and the rotor assembly in line with the rotor tip (from the tip side). Then drill and tap for a metric 6 x 1 bolt. Thread a bolt into the tapped hole. This bolt will act as an additional locator in the wide notch of the distributor shaft.

The next part is the most critical. A nominal 3/4 inch hole will need to be cut in the center of the circular piece of plastic so it will fit snugly over the threads on the adaptor. This will need to be centered carefully to insure that the magnets rotate in a near perfect circle. It can be tested on the distributor after it has been removed from the car. A 3/4 inch conduit threaded lock ring will be tightened to hold the disc on to the rotor until you are ready to permanently fuse the assembly together. The magnetic ring will be fastened to the 3 inch plastic circle by drilling two holes to receive the two mounting screws. Exact centering of the ring is crucial.

At this point the distributor should be removed from the car. Make sure the trailing (sev) rotor contact is pointing towards wire #1 and "pmh" (tdc) is visible in the timing hole of the bell housing (this is top dead center for cylinder one one the combustion stroke). The rotor tip needs to face in the same direction as the large notch on the distributor shaft (the 6 mm screw will fit into the wide slot). With the rotor-magnet assembly mounted on the distributor shaft, rotate the shaft and make necessary adjustments to keep the ring level and centered.

This is the procedure for mounting the Pertronix sensor on an exterior bracket instead of an internal base plate originally used.

I used a deep electrical box. Choose one with only one knockout on the bottom. (some have five on the bottom) I don't know if these are round boxes or hexagonal boxes. They have four flat sides and four corners with radii that "match" the outside radius of the distributor. You can get two brackets from one box if you cut correctly. I used an abrasive disc in a pneumatic cut off tool. You want to save the two corners without the mounting tabs on them. With the box upside down measure approximately two inches to the left of the middle of the radius and two and 1/2 inches to the right of the middle of the radius. Rotate the box 180 degrees and make the same marks on the other side. Scribe a line between the two marks on each side. Cut the box in half staying well away from the scribed lines (extra material is good for now). Make vertical cuts on both sides of the radius and then cut the sides off so all that is left is the radius and the bottom of the box.

At this point I tried the bracket on the distributor and ground it back until it would fit inside the distributor with the radius on the outside. You have to do some undercutting and creative grinding because the bracket is on the out side of the distributor and the mounting surface is on the inside. You may also have to give the distributor cam some additional clearance.

Fit the sensor to the bracket. One of the existing holes matched the pertronix hole exactly on my bracket. You want the sensor to be in the middle of the radius and as far forward as possible. You will have to enlarge the existing hole from the box. You probably will have to grind some of the Pertronix bracket back to match the bracket you made but this can be done later. When one hole is located, mark the second one and drill it. With the rotor assembly on the shaft, test to see if the sensor will be too high. Mine was too high every time so I put the flat part of the homemade bracket in a vice and bent the curved part down a little. Lots of trial and error here. I used 1/4 inch screws, nuts and loctite to mount the sensor. If there is end-play in the shaft in excess of the Pertronix specifications the shaft will have to be shimmed to reduce it. Drive the gear roll pin out and shim above the gear. You must limit the magnet clearance to less than .060 inches.

When all seemed right, I took two stainless steel hose clamps from the plumbing supply (stronger than automotive type) and clamped the bracket to the distributor facing the clamping screws in opposite directions in case vibration should loosen one of them. The clamps allow for easy positioning of the sensor from side to side. Remember to put some white out on the face of the sensor right below the yellow dot. The whiteout should be inbetween two of the 45 degree magnets when the rotor is pointed half way between #1 and #6 (at the distributor cap mounting hole)

The lock nut should be lightly tightened so the magnetic ring can be rotated to achieve approximate firing position. Leave the sensor in the center of the window. This may be the final position. A very accurate positioning can be achieved by pointing the rotor at the cap mounting hole on the distributor body nearest wire #1 (this is half way between wire #1 and wire #6 and therefore the sensor's firing point should be halfway between two of the 45 degree magnets). (firing order is 1-6-2-5-3-4 ccw). When everything is in sync put white out on the mating parts and tighten the lock nut firmly making sure the parts don't shift. At this point, if you are sure everything is lined up, centered and rotating level, use JB Weld (epoxy) to permanently fasten the adaptor to the circular disk ("JB Weld Quick" sets in four minutes and cures in four hours). Any minor discrepancies can be made up by sliding the mounting bracket. NOTE: After one year the "quick epoxy" cracked and the magnetic ring rotated out of sync with the rotor. I redid the epoxy with "regular" JB Weld and put a little thread lock on the lock nut.

Now normal timing procedures involving rotating the distributor body apply. When refitting the distributor have the "window" pointing roughly towards the right front tire and the tip of the rotor just before (ccw) the mounting hole on the distributor. Rotors can be replaced by simply removing the 6mm screw. I had difficulty with cold starts and flooding so I replaced the coil with a Pertronix 40,000 volt coil (about $30 from Retro Rockets). I now believe I was just overchoking the car. Use the choke sparingly if at all. Pertronix specifies a minimum of 1.5 ohms resistance across the coil terminals and recommends wires with 500 ohms of resistance per foot. I'm using solid core Packard wires with good results.

Any mistakes will probably take place on the plastic parts which usually cost about $2.00. So buy a couple of pvc box covers in case you don't get it right the first time. There is only one 6 cylinder Mopar cap that matches the 86mm distributor body NAPA MO40SB $16 NAPA. The Mopar rotor is NAPA MO13 and costs about $4.

You will of course have to recalibrate the tach because all readings will be doubled (one coil doing the work of two). Lower the steering wheel and remove all the screws around the instrument cluster including the guages. The lower dress panel has to come loose also. The cluster will pull forward with some jiggling. You will probably have to disconnect the speedometer cable to pull the cluster far enough forward. Watch for wire connectors that might accidentally pull off of their pins. At the bottom of the tach there is a piece of paper tape covering the adjustment hole which can be removed or punctured. A long thin screw driver can be inserted into the hole to adjust calibrate the tach (finding the screw slot is a bit of a problem). I had to turn mine down all the way and it may be reading as much as 25% high.

I still believe the HEI conversion is the best. I originally did this with an ill fitting Subaru cap which entailed much extra labor. A one piece injection molding to mate the rotor to the magnet ring and a molding for the bracket would eliminate almost all of the labor involved. Make sure you understand what you are going to do before you do it. Although it is fully functional, this should not be considered a finished project. It is only the beginning. I've created this web page which I will use to update the project as suggestions are put forth.

I have found a 86mm mopar 6 cylinder cap and matching rotor that fits the sm distributor. NAPA cap #MO40SB and NAPA rotor #MO13. Only two modifications are necessary. The cap requires two retaining tabs to be fashioned and screwed down to the SM distributer with Metric 5x80 cross head screws. The rotor must have the rivet that holds the tip driven out and a "wide tip" fashioned that is equal to one half the distance between two of the ignition wire posts. I used a "sabre saw" blade as a source of strong material to grind a new tip. Insert the rivet through a freshly drilled hole in the new tip and the spring contact. I filled the cavity under the rivet with JB Weld epoxy. The locating tab inside the rotor will fit in the narrow slot in the distributor shaft with some gentle tapping with a wooden drift. An appropriately sized bushing will need to be fashioned to fit the rotor into the assembly carry the magnet ring (above). When all is fitted a hole (6 mm) will need to be drilled and tapped though the rotor, the bushing and the assembly. A 6mm bolt will then act as an additional locator on the distributor ahaft through the large slot. The rotor is slightly larger than the distributor shaft and will need to be shimmed slightly. I used the finger off of a nitrile glove which should withstand the temperatures encountered here. The height of the magnet ring in relation to the sensor and the height of the rotor itself will need to be monitored through this process. After this modification, my engine started up immediately and only needed a slight tweaking of the timing.

Carsten Bussmann in Germany has made an excellent commercial version of this modification. Visit his (three language) website for more information.

Carsten's web site

Stan George