The first generation Capacitance Discharge
Ignition, CDI,or 610759 Solid State Ignition, SSI, common on early HH 100 and HH 120 Tractor engines had no trigger pins on
the flywheel, but put the electronics under the flywheel. The ESKA single cylinder outboard motor ignitions, 610851 are almost
identical, the difference in them is that the outboard motor has a mechanical spark advance and only one trigger coil. Figure 2-1, GamefisherTractorSSIsm.jpg shows
the 610759 under the flywheel SSI and the ESKA single cylinder outboard motor ignitions side by side. Since they are almost
identical, I will cover them here together.
There are two different internal configurations
of the 610759. One I call 610759A which has a printed circuit board inside and the wires coming out of the Charge Coil are
both Black. The other configuration, 610759B has one Black wire and one Red wire coming out of the Charge Coil and no printed
circuit board ( the wires for the components are connected directly to each other using a fiber board.) See How it works and
Schematics for more detail. The ESKA 619851 that I have seen had two black wires coming from the Ignition Charge Coil and
a printed Circuit Board and I was able to repair them like the tractor 610759A. The repair here concerns only the 610759A
and the ESKA.
A good place to start is initial test procedures
to avoid guessing, but first a few do’s and don’ts first
Do’s and Don’ts
1. Don’t ever crank an engine with out a
grounded spark plug attached to the ignition wire, see Figure 2-2 Spark Tester. The output voltage of the ignition increases
until it is high enough to arc the plug gap. With out a spark plug attached, the voltage will continue to increase until it
arcs somewhere else inside the ignition where it can do permanent damage. If the engine is running, never remove the spark
plug wire to kill the engine; shut off the fuel.
2. Don’t assume an attitude of guessing
at what has failed, buying and installing parts only to realize that it was not the part that failed. Instead, do some detective
work to gather the facts which point to or isolate the failure. Start with the simple and easy tests first, even if you think
the failure is elsewhere.
3. If you ask for help on one of the many
internet yahoo engine or tractor clubs like http://groups.yahoo.com/group/tecumseh_engine_group or http://groups.yahoo.com/group/eskaoutboards
, give a complete description of your engine with the model numbers. This will help those trying to help you to know the configuration
that you are talking about.
4. If you don’t already have a Volt /
Olm meter get an inexpensive one at Sears, Walmart or an auto parts store. This will save a lot of guessing and frustration.
My $10 analog meter looks like Figure 2-3, MeterA.jpg. If you set it to Ohms and touch the leads together, the needle will
go to zero, no resistance as in a short. If you leave the leads separated, the meter will read infinite ( very high) resistance
or an open circuit.
Testing Before SSI Removal
Test for Spark
Usually checking for a spark is a good place
to start. Figure 2-2, SparkTest.jpg shows a home made spark tester which can help protect from causing damage. Removing the
spark plug from the cylinder head provides compression release and reduces the stress on the battery, starter motor and rope
puller during testing.
I use inductive timing light and have had problems
with it not working on a weak sparks. This I have resolved by running the spark wire thru the pick up twice instead of just
once. See Figure 2-4, TimingLight.jpg. This doubles the spark current sensed by the timing light and fires off the weak spark.
Sometimes there is not a sufficient length of spark wire, so I made an adapter with the loop in it to place in series with
the wire to the spark plug. When the normal timing light won’t fire off a weak spark, but with the loop does fire, I
conclude the ignition has a weak spark and has failed. It is like a go / no go test.
Engine Kill Wire Check
Engines with magnetos as well as electronic
ignitions like the Solid State Ignition, SSI, are shut down by grounding out the ignition. Sometimes the tractor or outboard
wiring between the key or kill switch and the engine gets shorted to ground, thus always killing the ignition. An easy way
to check for this is to disconnect the kill wire at the engine to separate the tractor wiring from the engine wiring.
For the tractor engines, there is a nylon terminal
connector that comes out of the blower housing for the connection of the kill wire. See Figure 2-5, Kill-Connect.jpg If you
disconnect the kill wire at the engine and then get a spark, then there is a problem in the tractor wiring, not the ignition
For the outboard, there is either a push button
to kill the engine or a contact at the end of travel of the throttle lever. It has been reported that if one lets go of the
push button before the engine has come to a complete stop, that ignition failure has resulted. The manufacture recommends
killing the engine by using the choke.
I suspect that if the engine bounces back from
compression, turning backwards, there is a reversal of the magnetic field in the charge coil that was not planned for in the
design. If it were my outboard, I would disconnect the kill wire at the Electronics Module of the ignition and secure it.
Do this and then check for a spark.
Spark Plug Connector
Another common problem with Tecumseh engines
is the connector at the spark plug. Measure the resistance from the connector to the engine block. The resistance should be
4,000 to 7,000 Ohms. If it is erratic, in the meg ohm range or open, cut off the boot and re-measure directly from the stranded
wire. If it now checks O.K.,hook the wire directly to the spark plug until
all else is fixed and then replace the connector with a Briggs and Stratton 493880S or 66538S or Stens 135-081. If the spark
wire is still open, it may have a poor connection at the other end of the wire. After all the other testing is completed,
you can use what ever force is necessary to pull the spark wire out of the SSI and will find a small brass nail in the bottom
center of the hole. Measure the resistance from that pin to ground. If it is still open, there is likely an open circuit in
the secondary winding of the Pulse Transformer and the Pulse Transformer has failed. If there is the nominal resistance from
the pin to ground, clean out the hole and replace the spark plug wire with new stranded core wire.
Before you remove the SSI from the engine (
or the Electronics Module from the mounting plate), make some scribe marks around the screws so you can put it back where
you found them.
Beyond that, you can mail the ignition to me,
including the Pulse Transformer and I can run it on the engine simulator to verify the failure. If the tests above show no
failure except there is no spark, then it is most likely that the main capacitor in the Electronics Module has failed and
you have three options:
1. Replace the main capacitor with a new one.
2. Look for a replacement. Good luck.
To repair the SSI, you need to remove it from
the engine, but leave the Electronics Module mounted if you can. With the SSI removed you can do two ground checks. Notice
where the Ignition Charge coil is grounded and measure the resistance between the mounting plate and the ring terminal. I
have found corrosion here causing a fault. It should be zero. Similarly notice where the Electronics Module is grounded and
measure the resistance between the mounting plate and the mounting stud. I have found epoxy in this connection causing a fault.
Also, check the Ignition Charge Coil by measuring the resistance between the frame and the disconnected lead at the Electronics
Module. It should be about 940 Ohms.
More than 90% of the failures of these ignitions
are the main capacitor so it is cost effective to just replace the failed component. To do this, we have to remove some of
the epoxy covering the Printed Circuit Board, PCB in the Electronics Module, See Figure 2.6 Unwrap.jpg. I use a small butane
torch to heat the epoxy then carve the edges off with a Stanley knife. Then heat the top and pop it off with the point of
the knife. Then put a damp towel on it to absorb any heat. Most of the heat goes off with the hot shavings so you don’t
want to get them on bare skin.
This exposes the PCB as shown in Figure 1-7,
610759AFix.jpg. The ESKA ignition is the same. The configuration shown is a 610759A, but there is also a 610759B that does
not have a PCB inside.
You can see one trace is cut to disconnect a
diode and a jumper is placed across the failed capacitor. After testing, the Electronics Module is sealed up with silicone.
The cut frees up the terminal that went to the
Pulse Transformer so we can use it to locate a new capacitor out from under the flywheel. The new capacitor has a higher voltage
rating and is thus physically larger. For the tractor installation, the new capacitor is mounted on the Pulse Transformer
along with a new diode. As shown in Figure 2-8 610759PTFixSm.jpg before the adhesive was applied.
For the outboard, the new capacitor and diode
are proposed to be package in a small assembly that can to be mounted somewhere on the frame. See Figure 2-9, CapDiode1.jpg
In final kit form, the assembly would have longer
shrink wrap to accommodate the nylon cable clamps that I added. For the tractor wire harnesses that I have made, the various
connectors are supplied loose, so the wires can be cut to fit the installation. The concept here is the same as that for the
ESKA twin. Wouldn’t it be nice if someone like Doug Street provided the kits already assembled and ready to mount and
I should note that the original capacitors had
a voltage breakdown rating of 250 Volts which I consider too low which is why they are failing. I have used 600 Volt which
may be over kill. A 400 Volt would likely be sufficient and would be smaller physical size so that is used here. The capacitance
value is 1mf, micro farad. Not just any capacitor is suitable for this application because of the high peak current and high
power constantly being moved into and out of the capacitor. A filter capacitor is not suitable. The capacitor are made of
metalized polyester film and needs to be made for energy storage / discharge . The use of two .47 mf capacitors in parallel
would cost about half as much.
test all these ignitions on engine simulators before and after repair. You could just install the repaired ignition and repeat
the test for a spark.