The Atwater Kent Ignition System

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6 Windward Dr. Severna Park, MD 21146

This excellent ignition system is unlike most ignition systems using a coil, distributor and battery; thus, one must pay careful attention to the manufacturer's instructions if damage is to be avoided. The system basically consists of a special distributor and special coil. The distributor is called the 'UNISPARKER'. This name apparently was derived from the Latin 'uno' meaning 'one'. The 'UNISPARKER' makes one spark for each distributor point closure. In this system the coil is specifically designed to work with the 'UNISPARKER'. It is not likely that the substitution of a conventional 6 volt automotive coil will prove satisfactory due to the extremely short time (DWELL) the 'UNISPARKER' points are closed. The points must not be set 'closed' if the system is to operate. The points should be set 'open' .010 to .012 inch, never closer. There are no other adjustments. The movement of the points is so fast the human eye cannot follow the motion. Don't file or grind the parts of the 'UNISPARKER' thinking you will get the points to move. The parts are hardened and should never need to be changed.

The 'UNISPARKER' was made in several versions. The type 'K-2' operated clockwise, only; whereas, the type 'H' (without automatic spark advance) was available for either clockwise or counter clockwise operation. It should be noted that only the specified rotation will provide correct operation with the 'UNISPARKER'. It will not operate in both directions, as a timer will, on a direct reversing engine. Note the direction of the notches in the shaft. The correct rotation of the shaft is in the direction that drags the 'lifter' in the direction the shaft is turning. As the shaft rotates, the 'lifter' will be forced off the shaft, bumping the 'latch', which closes the points so fast that it appears nothing happened. Placing a finger lightly on the point spring should reveal slight movement as the 'lifter' snaps back. One needs to insure that the parts, such as the 'notched' shaft, 'lifter' and 'latch', are kept clean and oiled regularly with a light weight oil. The manufacturer makes no mention of grease for lubrication; however, when the 'UNISPARKER' was designed in 1904, there may have been no suitable grease available. The 'lifter' spring tension is very light and oil is probably a totally satisfactory lubricant. The spring tension seems to be approximately 150 grams to cause the 'lifter' to just move toward the 'notched' shaft. The spring tension measurement is made with the distributor in its normal operating position ('notched' shaft in a vertical position). The gram gauge should be horizontal and in line with the spring. Perhaps the most significant point to be made in servicing the 'UNISPARKER' is that if you treat it like a fine watch it should give excellent service. The system is very conservative in battery power; and, even if the engine is stopped with switch 'on', no power is consumed, because the points are normally open.

The coil generally used with the 'UNISPARKER' is the ATWATER KENT SYSTEM TYPE-K. This model of coil also seems to be the one most often seen at flea markets and shows. The Type-K coil is approximately 8'L x4'W x 3'H. On the top there is an 'ON/OFF' switch and a contactor labeled, 'START'. The START contactor is used to start an engine, assuming it is at the right position in one of its cylinders and the last time the engine was stopped one remembered to choke the engine just before it stopped rotating. This will suck a charge of gasoline into the cylinders. Typically, an engine will start as much as twenty four hours later using the START contactor, provided the cylinders have a charge of gasoline.

On the side of the TYPE-K coil one will find six binding posts arranged as follows:




The 'Plug' binding post has a domed bakelite insulator cover. The 'Plug' is connected to the center tower of the 'UNISPARKER' distributor cap. The GRD (ground) should be connected to the frame of the engine. Assuming the system is used with negative ground, a wire connecting GRD and NEG 6 to the engine frame may be employed. The POS 6 lead is connected to the POS 6 lead on the battery. An on/off switch may be inserted in the POS 6 lead if desired. One may choose to use the 'ON/OFF' switch on the coil, instead of an external switch. One should maintain the battery polarity specified on the coil. Both of the binding posts connected to the 'UNISPARKER' are labeled, 'Int'. The two 'Int' binding posts are connected to the 'UNISPARKER' using two fourteen gauge stranded, insulated wires twisted together, the same way as old time lamp cord. This is most important and the manufacturer warns it is essential, to avoid damage to the system. The exact reason for

twisting the 'Int' wires together is not stated, but one could assume it has something to do with circuit electrical resonance, or it provides the necessary capacitance across the points. It should be noted that there is no external condensor (capacitor) across the points in this system and one should not add one thinking it will improve the point life or electrical performance. The 'UNISPARKER' points are tungsten, not platinum, and one should not file or attempt to clean them. Tungsten has a dark gray color and, unless or for some reason the points are grossly pitted, it is best to leave them alone. One of the frustrating characteristics of tungsten is that its surface resistance has to be broken down by a voltage often as high as twenty volts. This means that sometimes a set of tungsten points that hasn't been used for a long time will seem not to pass sufficient current to produce a strong spark when first used. Typically, this problem will go away after a few contact closures, so it is wise not to try to clean the points until they have had a chance to operate a few times. The '20 volt' contact resistance is normally overcome in a six volt system because the inductive kick of the coil raises the voltage well above six volts across the points.

It should be noted that the number of 'notches' in the distributor indicates the number of cylinders the engine may have. A single cylinder engine can use any of the multiple cylinder engine 'UNISPARKERS'. A three cylinder 'UNISPARKER' will have three 'notches' 120 degrees apart. A four cylinder 'UNISPARKER' will have four 'notches' 90 degrees apart. The four cylinder 'UNISPARKER' can be used for a two cylinder two-cycle engine if you use two spark out-puts 180 degrees apart. A four cycle two cylinder engine with the crankshaft arranged at 180 degrees will require using two spark out-puts 90 degrees apart. A two-cylinder four cycle engine with the cranks on the same side of the crankshaft will require that

the spark outputs are placed 180 degrees apart. One must not forget to insure the correct distributor shaft rotational speed and firing order for the number of cylinders in the engine; and to ground any spark outputs not used in a given configuration, to protect the coil from excessively high voltage due to no spark plug load. It should be noted that slow speed rotation of the 'UNISPARKER' does not change the spark output because the rate and duration of closure of the points is controlled by the action of

the 'lifter' return spring on the 'lifter' when it is forced off the 'notched' shaft. This clever design avoids the need for cranking the engine at a high rate of speed or the need for an 'impulse' coupling.

The 'UNISPARKER' remained in production for approximately 30 years, essentially unchanged. This speaks well of its attributes and customer acceptance. It is hoped the above material will clear up some of the mystery surrounding this unique and remarkable device.