The Atwater Kent Ignition System

By Staff

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:

INT O O NEG 6

PLUG O O GRD

INT O O POS 6

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.

  • Published on Jun 1, 1985
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