Engines&Magnets
Home | 1.Tecumseh Ignitions-Part 1, SSI Replacement | Part 2 Tecumseh SSI Repair | Part 3, Point Condenser Magnetos | Part 4, ESKA Twin | Att 1, How a it Works / Schematics | Att 2, Autopsies | Att 3 SSI Charge Coil and Stator Test | Att 4 Flywheel Magnets | Att 5. Replacing 610759 SSI | 2,Other Ignitions | 3. Antique Engines | 4. Vintage Generators | 5. Vintage Tractors | 6. Gaussmeter / Hall Effect | 7. Ed's Trading Post | 8. Miscellaneous
1. Tecumseh Ignitions-Part 2, SSI Repair,

SSI Repair,619759/ESKA Single

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.

gamefishertractorssism.jpg
Figure 2-1

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.

sparktest.jpg
Figure 2-2

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.

meterasm.jpg
Figure 2-3

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.

timinglights.jpg
Figure 2-4

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.

kill-connectsm.jpg
Figure 1

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 system.
 
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.
     3. For the tractors, see Dale Colvert’s site www.overnightsolutions.com
 
Ignition Repair
 
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.

unwrap.jpg
Figure 2-6

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.

610759afixsm.jpg
Figure 2-7

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.

newcap1.jpg

ptmod1.jpg
Figure2-8

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

capdiodesm.jpg
Figure 2-9

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 plug in.
 
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.
 
Final Testing
 
I 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.