After failing 3 old tech coils (see dead stick landings) with the OEM distributor, I was looking for something better and this is what I worked out.

I wanted a Waste Spark system but like everyone I did not want to take out a mortgage.

GM domestic since 1987 had been using a distributor-less ignition system using a Waste Spark method of spark distribution.

Each cylinder is paired with the cylinder that is opposite (1-4 or 2-3). The spark occurs simultaneously in the cylinder coming up on the compression stroke and in the cylinder coming up on the exhaust stroke. The coil has two secondary wires (spark plug wires).

The cylinder on the exhaust stroke requires very little of the available energy to fire the spark plug. The remaining energy will be used as required by the cylinder on the compression stroke. The same process is repeated when the cylinders reverse roles.

GM tends to build-in a reluctor (disc with slots) on their crankshaft it is like a flywheel casted into the crank. They install a magnetic sensor that protrudes into engine block within approximately .050" of the crankshaft reluctor. This reluctor/wheel with seven slots machined into it, six of which are equally spaced (60° apart). A seventh slot is spaced 10° from one other slot and serves to generate a sync pulse. As the reluctor rotates as part of the crankshaft, the slot changes the magnetic field of the sensor, creating an induced voltage pulse. Based on the crank sensor pulses, the Direct Ignition Module sends reference signals to the Electronic Control Module (Computer that operates the engine) but we are not using the Computer. The Direct Ignition Module will operate on their own but usually after the engine achieves 400 rpm the ECM takes control, this is how they control timing. If the DIS does not receive a signal from the ECM it will stay on back-up mode with a fixed timing curve. In our case by simply not hooking up wires to the ECM the DIS module will operate on the back-up program. And very happy too!

The DIS module monitors the crank sensor (two wire) signals. By comparing the time between pulses, the DIS module can recognize the pulse representing the seventh slot (sync-pulse), which starts the calculation of ignition coil sequencing. The second crank pulse following the sync-pulse signals the DIS module to fire the #2/3 ignition coil and the fifth crank pulse signals the module to fire the #1/4 ignition coil. In sort every 180° of the crank it will fire one coil, each coil fire 2 spark plugs. If one plug lead from the same coil is disconnected spark plug lead acts as one plate of a capacitor, with the engine being the other plate. It will only fire the one plug, miss fire will take place.

Coils are controlled by the DIS module, the module controls the ground signal to the primary winding of the coil. The positive may also be feed by the module but not essential. Because of the direction of current flow in the primary winding, and thus in the secondary winding, one plug will fire from the center electrode to the side electrode while the other will fire from side electrode to center electrode. It will spark, don't try it on your body 40,000 volts may be available.

We will drill some holes into the harmonic balancer, install two off-the-self magnetic sensors to be within .050" of the holes. Each magnetic sensor will have two wires going to the DIS module, I recommend to install 2 DIS modules. Each module will need a power feed and a good ground, also recommend to install the modules inside of fuselage, to be dry all the time and away from heat and vibrations. Now each module will have two wires out, these are the ground circuits for the two coils that will fire the same. If we only had one module the two ground signals would connect direct to the pair of coils, only need to figure out witch is #1/4 and #2/3. Since we will run two modules we need to take the four wires to a switch (dash mounted) and two wires from the coils will meet at the same switch, now the pilot will select witch module will operate the coils, dual up to coils. Loose one coil two cylinders go down. Sensors, modules may be purchased at auto supply place, GM stores or junkyard. The modules and coil are designed to be bolted to the engine, but I recommend not to.

If you follow how I did it you will end up with one sensor at about 8° BTC and the other at 28° BTC, why because you need space for the two sensors to be mounted around the arc of the outside surface of the harmonic, you could install the other magnetic sensor 180° on the other side of the harmonic balancer, one reverses the coil grounds from that module and it will also work, but now you need to make a bracket for the other side of the engine. More weight, more work.

You will be surprised to find that the engine will start as normal as your car on either sensor; the advanced sensor will not cause problems. Reason is that the engine needs to turn a full revolution prior to the DIS module fires the coil, when it does the engine is over 100 rpm, that is why it will not be a problem.

The DIS modules only have about 10° advance curb. The 28 will end up at 38° full advance; you set it and forget about, no adjustment required after initial set up.

The bracket that holds the magnetic sensors will have small movements available to precise set the initial timing. We will use the flywheel side as the reference; there are 100 teeth on the ring gear 3.6° per, 10 = 36°, 5 = 18°. Using the harmonic timing mark at 0 you will be able to scribe a line on the flywheel side paint the desire tooth. Start the engine rev-up to 5000 rpm using timing light to check the timing; this is done prior to mounting a propeller. You have to make sure that the full advance will not exceed 38° BTC, if it does, it may damage your engine, pre-ignition will damage your pistons may lead to total engine failure. The other magnetic sensor you will be able to use the harmonic side projecting the timing light on the timing belt cover as would in the car.

You will not be able to hand prop start engine, because it needs almost a full turn of the crank for the DIS module to figure out when is #1 going to be at top of travel.

We have harmonic balancer with a place for an air condition compressor belt, depending on what model you have (see pictures) we need to slot this part, but it will be easier to drill. If you have access to a dividing head it is the most precise, if not starting with the timing mark used to adjust engine timing (distributor) you need to divide 6 even spaces. Steel valve cover engine uses 4 screws to secure the harmonic balancer this unit has a 3/8" flat area, this is the place to install the holes, you need to drill 5/16" holes, control the depth they should all be the same about .200" at center of drill. This task can be done in a drill press, don't try free hand (hand drill). It needs to be accurate. Diving free style, start with timing mark, measure the diameter of flat area about 144 mm =5.6692/3.14= 17.801/6 = 2.9668" apart, using drafting compass adjust until you have 6 equal marks around the circle or a piece of masking tape worked out in a flat table. Center punch mark the six slots.

Total distance of circle 17.8"/360 = .04944" x 10 degrees = .4944", you need to place the seven slot about .5" from one other. Place the harmonic on a flat table with the crankshaft side down, identify the timing mark, find the punch mark to the right of the timing mark (first slot) .5" before the first center mark, punch the center of the seventh slot. Drill all seven holes projecting the center of the circle, if using drill press clamp harmonic unit, again be precise. If you have access to milling machine with divider head it is easier; identify timing mark (wedge), drill 5/16" to .200" depth, rotate 60° drill, rotate 60, and so on, when back to timing mark, dial 50° drill and your done. Turning is to right hand same as engine rotation of part. This part should be re-balanced now, and painted after.

For this to work you need to install the magnetic sensor at the right place. The 28° sensor will be at 100° from the timing wedge when same wedge is set a 0° of the timing cover, this means #1 piston is at top of travel on the cylinder, the camshaft and crank are lined up for valve timing. The sensors should be centered with the slots (holes) and about .050" from the surface (flat area) of the harmonic balancer. Follow the dimension of the drawings for the brackets and it will work out.

Newer engines, alloy valve cover use a forged steel harmonic pulley 5 holes to bolt to crankshaft and one hole for indexing. This type of pulley you need to machine the outer Polly "V" grooves flat, this was for the a/c belt, then follow same process. You will drill right true the flat area. The sensors need to be positioned further out to the firewall and closer to center of crankshaft for this pulley.

If you are planning to use electronic fuel injection like Racetech Inc. then follow their procedures to install the magnets.

jim@nessaaircraft.net

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