Tecumseh Solid State Ignitions Replacement

Engines&Magnets

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Page 3, SSI Replacement

Section 1 Auto Ignition Conversion using Trigger from Failed SSI

Created 24 September 2008

Edit note: The older material on this web page has been moved down.

For conversion of the 610759 ignition also see http://overnigh.startlogic.com/page8.html .

1. INTRODUCTION

Figure3-1-1

The earliest Tecumseh Capacitance Discharge Ignitions, CDI or Solid State Ignition, SSI is the 610759 (the under the flywheel version) which have been out of production for many years and is virtually unavailable.. I see the above the flywheel, 610906 and 610748 SSI going the same fate. I don’t think they are in production and the prices of what is left seems to be increasing. So some new options for a conversion to an automotive ignition might be timely. I have a few of the trigger coils that I made a few years ago,( Brian Miller offers them to, http://gardentractorpullingtips.com/ignition.htm ),but have been toying with using the idea of using the Trigger section of failed Tecumseh 610906 , 610748 and Onan NB SSBI (Solid State Breakerless Ignition) for several years. I have noticed that the trigger section of these three look all the same, so by I will address all three at once. Initially, I found that the trigger section had failed, but some of those failures I may have induced myself. Then I found that the SSI trigger voltage was too high and was over driving the circuit in the automotive Control Module. While trying some signal conditioning circuits, I discovered that I could easily and simply overcome this problem by adding a diode. We can easily adjust the trigger voltage by increasing or decreasing the air gap between the Trigger Pin and the Trigger coil / magnet. This allows us to retain the automatic feature of retarding the spark for easy starting and yet have an advanced spark for more power. The next paragraph outlines the very simple installation and is followed by the details of the modification.

2. INSTALLATION

Figure 3-1-1, ( 3up.jpg) shows the modified SSI. The spark plug wire is cut off as it is not needed , cleans things up a little and is a clue to not try to use the modified part in the OEM configuration. The trigger section is shown as this is the part we need for the automotive conversion. It consists of a magnet and a coil of very fine wire which , of coarse has two ends. One end is grounded internally and the other is routed to the terminal for making easy connections.

Step 1

Remove the wire from the terminal that comes from the stator, tape it up and secure it. This wire was used to charge the capacitor in the SSI, but is no longer needed and still has several hundred volts on it.

Step 2

Remove the failed SSI or SSBI. Send it to me if you don’t want it.

Step 3

Install the modified SSI setting the initial air gap between the tall trigger pin and the trigger magnet to the gap sent with the modified unit or .010" for the 610906 or the maximum the slot in the mounting screws will allow for the 610748.

Step 4

Install the Control Module, Ignition Coil, Spark plug wire, ballast resistor ( if needed) and new ignition switch. See Figure 3-1-2, NAPABoys.jpg and Figure 3-1-3, Coil.jpg

Figure 3-1-2

Figure 3-1-3

The Control Module is a Transistor ignition switch that replaces the points. The trigger generates a timing pulse for the transistor.

Figure 3-1-4

Step 5

Run the trigger signal wire from the terminal on the SSI/SSBI to pin B on the control module and wire the automotive components. See the block diagram, Figure 3-1-4.

You can also find some good information at other websites:

Help . I need some help here.

Step 6

Check all your connections. Remove the spark plug, ground the threads and connect to the ignition Coil.

Step 7

Apply power. Note: when you apply power, you should see some sparks at the spark plug. If you don’t have some sparks, recheck your wiring.

Step 8.

Turn the flywheel over by hand. Look for a spark as the tall trigger pin passes the trigger coil / magnet.

Step 9

Set up an inductive timing light and aim it at the trigger. Turning the flywheel by hand at first, look for the flash of the timing light to illuminate the tall trigger pin at the trigger. Now, crank the engine with the starter motor. The timing light should illuminate the tall trigger pin at the trigger at first and then jump to the short pin as RPM increases. If the short pin is illuminated all the time, install an unconnected spark plug in the head to add compression and slow the engine down. If the air gap is decreased, the transition point should occur at a slower RPM. If the air gap is increased, the transition should occur at a higher RPM.

LIST of MATERIALS:

Added 28 April 09

Several have ask me for a complete kit for the conversion to the automotive type ignition. This is more than I can deal with so Mike Brooks, brokndwn64@gmail.com, has done a lot of work to put together a complete and cost effective kit in the spirit of helping folks keep their old tractors going again with out delay. I have tested the kit and sent him a few modified 610906 . Thus Mike can provide all the parts form one source complete even with the control module, wire, connectors, switch, Modified SSI and coil bracket. My only concern is that the failed SSI needs to be mailed to me so I can fill the pipe line with modified units. The kit looks like this:

Modification Kit

LIST of MATERIALS Continued:

Modified SSI Tecumseh 610906, or 610748 0r Onan SSBI

Control Module:

Wells............... CR 109

NAPA .............TP51SB

Ford ( Requires a ballast resistor).........

Ignition Coil: (* built in resistor)

Tecumseh*...............32080

Kohler* ...................231281 or 237256 ( NAPA 4151921S )

Mopar .....................4176009

Ford., Motorcraft.....D5TE-12029 Says on it" use with external resistor "

Foley-Belsaw.............5978730 ( $17.50 )

Delco Remy..........231281

STENS.................460-048 ($27.50)

Ballast resistor if required:

Wells......................CR 107 ($3.19)

NAPA

Ford

Ignition Switch which supplies power to the ignition not one that grounds out a magneto or electronic ignition

NAPA...................7-01854

Stens

ROTO

An inquary in October 2008 Indicates some 610906 and 610748 are still available as follows:

A. http://www.partstree.com/parts/ has the 610906 listed at $148.08 and the 610748 at $151.64.

B. M&D mower sold me a new ignition for my Tecumseh OH 180 for $130.00.

C. Tecumseh dealers and distributors have both in stock, 610906 $159.92 and 610748 $151.64 .

D. http://www.outdoordistributors.com/parts.html lists the 610906 for $139.28 and the 610748 as NO LONGER AVAILABLE, NLA

3. SSI MODIFICATION

A printed circuit board is made of a phenolic board ( white here) with a layer of copper on it that has been etched to leave the copper traces that make up the wires of the device. A green coating is applied to assist in making the solder connections. Modifications to the circuit are made using cuts and jumpers. A cut in the copper trace is like cutting a wire and a jumper is adding a wire. The modifications here include making one cut and adding two jumpers.

Figure 3-1-5

The modifications to the SSI are fairly simple, however extreme caution is required to avoid damaging the trigger coil. The 610906 is shown in Figure 3-1-5, 610906Bot7.jpg. The modification for those 610748s which use a PC board is essentially the same, but the Onan NB, Solid State Breakerless Ignition and some 610748 do not have a PC board, but has fine wires coming form the trigger coil and is very easy to damage.

The first thing to do is to cut off the wire to spark plug. Next we need to excavate the epoxy potting being careful to stay away from the trigger coil. I use a small Butane Torch to heat the epoxy then carve it off with an old dull screw driver. ( I know this sounds a little crude for the Spark Doctor, but it works.) It helps to heat the driver as you go. One has to use caution as the chips of epoxy that come off are hot. One could practice in an area away from the real modification. An alternative is to soak the unit in Acetone for a few days, then carve off a layer of softened epoxy. A couple of passes are required. At the terminal, I leave a pig tail of the wire attached to the terminal as it makes connecting the diode very easy. The easiest way to do this is to un-solder the wire from the PC board and push it towards the terminal. I also use a soldering iron to remove epoxy; the tip is shown in Figure 3-1-6. The trigger coil has one red wire and one black wire. If you expose these, you are going too far. I start the excavation away from the Trigger Coil and find the PC Board, then use the copper traces as reference to remove the epoxy until I have the trace for the red wire and the trace for the black wire exposed.

Figure 3-1-6

The black trace of the trigger coil is to be jumpered to ground. The ground screw is shown for reference and there is a large copper pad around it. Solder a short length of black wire on the black trace and the ground pad. By grounding one side of the trigger coil, we will need only one wire between the trigger and the Control Module. This works for the Wells CR 109, but I don’t have experience with the other control modules.

Figure 3-1-7

One cut has to be made on the trace connected to the Red wire as shown in Figure 3-1-5, ( 610906Bot7.jpg ). This separates the trigger coil from the original circuit. Now is a good time to measure the resistance of the trigger coil. Put one probe of an Ohm meter on the red trace and the other on the black trace. You should get 9 to 11 Ohms for a good 610906 trigger coil and about 100 Ohms for the 610748. If the coil is open, the SSI is trash. In order for the trigger to work , we need to add a diode. So using the diode as the jumper, solder the banded end to the red trace and the other end to the pig tail you left at the terminal. Now would be a good time to mount the SSI on the engine and test it. Start with an air gap between the trigger magnet and the tall trigger pin of .010". See installation above for testing. After the modified SSI tests good, remove the SSI and fill the cavity made from removing the epoxy with E6000 or a silicon adhesive. The modification to the ONAN SSBI is shown in Figure 3-1-8.

Figure 3-1-8

I have found that making the modifications got easier and improved at about the sixth one. So if you don’t want to make the modifications your self, I can do it for you, for $25 plus S/H. If someone wants to set up shop doing the modifications, let me know your email as address or web site and I can add it here.

Section 2

Tecumseh Solid State Ignition Updated September 13, 2005

Introduction:

Note: Dale Colvert has offered a replacement for the 610759 since this work was done. See http://overnight-solutions.com .

There are two Tecumseh Solid State Ignitions ( SSI ) configurations we are concerned with here:

The one on the left I call "SSI Under" for short because it is under the flywheel. It is also an older configuration. The parts are:

Flywheel P/N............610758

SSI P/N....................610759

Pulse Transformer....610760

The one on the right I call "SSI Above" for short because it is above the flywheel. It is also an newer configuration.

Flywheel P/N........611000

SSI P/N................610906

Charging Coil.......610965

The Ignition System Replacement for both configurations, is covered below. The Pulse Transformer Repair ( pn 610759 ) and Quick Fix SSI Repair ( pn 610760 ) are covered on seperate pages.

As a quick overview of the replacement, an SSI Above flywheel,610758, with it’s trigger Pins is shown at the below. Above the advance ( short ) trigger pin is the trigger coil. This is a PLASTIC sewing machine bobbin with fine wire wound on it and mounted on a 1/4 inch machine screw with the head facing down. A rear earth magnet is mounted on the head of the screw. When the flywheel rotates, a voltage is generated in the coil when the trigger pin goes by. This voltage is routed to the control module of a Chrysler ignition system and initiates the spark.

The details of the replacement are also available as a 11 page file in PDF format of about 1 mbits. It can be down loaded at http://home.fuse.net/stoller/SSI_Replacement.pdf .

The original Tecumseh engineering using two trigger pins of different heights is very ingenuous in that it allows the use of one trigger coil but automatically advances the spark with engine RPM.. When the trigger pins go by the trigger coil, it is the change in magnetic flux that produces the voltage. As RPM increases, this rate of change of magnetic flux increases and the voltage increases. At cranking speed, low RPM, the short trigger pin has too large of an air gap to generate a sufficient voltage to trigger a spark, however the tall, start pin has a closer gap and readily triggers a spark. As RPM increases, the shorter, advanced pin produces a higher voltage and triggers the spark before the tall start pin. This is important because one task in the modification is to adjust the distance of the trigger coil to have a just after TDC spark for starting the engine but also have it advance when the engine is running. These adjustments are made with a timing light and timing marks that we will be adding.

The sequence of the modification consists of:

Task 1. Preparation,

Task 2. Adding the Trigger Pins,

Task 3. Adding the Trigger Coil,

Task 4. Installing Automotive Parts

Task 5. Adjustment / Test

Appendix 1 Making the Trigger Coil

Appendix 2 Tractor Pulling Ideas

Task 1. Preparation

Remove the flywheel. If we first paint the outer circumference of the flywheel white, our pencil marks locating the trigger pins and timing marks will be easier to see. Then before painting the flywheel black, the use of narrow strips of masking tape at the timing marks will make them show up easily. After the white paint is dry, lay the flywheel fin side down. We can use the key way for the woodruff key to locate a master reference line by installing a 3/16 piece of square key stock , at least 2 inches long, into the key way. Using a straight edge and clamp, mark both sides of the key way at the outer part of the flywheel as shown. Locate the center of the two marks and carry it around the edge to the outer circumference of the flywheel. This is the master reference line for locating the trigger pins and timing marks.

spare

A little about the ignition timing. The long trigger pin is about 3 Degrees After TDC and the short trigger pin is about 17 degrees Before TDC. With a circumference of 24 or 24.5 inches, one inch on the circumference is 15 degrees. Also, on my HH-120, there is a convenient window to shine a timing light to observe the actual spark timing when the engine is running if one puts the timing marks there. This window is under the badge ( which has the model and s/n ).

The layout of the timing marks is shown in blue above. Starting at the master reference line, measure 2 inches to the left for the TDC mark and 1 inch to the left for the 15 degree mark. Divide the inch between them into thirds for the 5 and 10 degree marks and use the same increment for the 20 degree mark. This position should put the timing marks in the window for the timing light. Also, only for the flywheel that already has the trigger pins, measure a line 3/16 to the right of the long trigger pin for a line that represents TDC with respect to the trigger coil which is to be added. Put thin strips of masking tape on the timing lines and paint the flywheel black.

Task 2. Adding Trigger Pins

For the configuration with the SSI Above the flywheel, the trigger pins should already be in place and this task can be skipped. Note: The flywheel from my HH 120 SSI Above, p/n 611000, seems to fit the HH1120 which has the SSI Under flywheel p/n 610758, but both have external motor / generators. Given the option, I would change flywheels rather that add the trigger pins. The original ignition components, except for the magnet on the flywheel, should be removed as they would no longer be used. If there was a stator under the flywheel for charging the battery, the flywheels may not be able to be switched.

For the older configuration with the SSI Under the flywheel, the task here is to install the trigger pins. Set the flywheel on a very flat surface and using something 1/4 inch thick, scribe a mark 1/4 from the back side of the flywheel. It is important that the long and short trigger pins be the same distance from the back of the flywheel so the center of both trigger pins track the center of the trigger coil or one might have trouble making the final adjustments. The long trigger pin goes on the intersection of this line and the master reference line. Measure 1 3/8 inches to the right of the master reference line to similarly locate the short trigger pin. I found a measuring tape for sewing flexible to fit the curve of the flywheel but checked if for accuracy with a steel tape.

Also, if one compares the locations of the trigger pins from the older SSI Under with those of the newer SSI Above, you will note that there is a difference in trigger pin locations. This is because there is a bolt which holds the magnet which is too close to where the short pin would go if they were the same. The trigger pins to be installed and the trigger coil are offset to the left to avoid this problem. Caution, the flywheel is balanced by drilling holes in the back to remove some weight. Check to see if one of these holes is too close to the trigger pin location.

Center punch the trigger pin locations, put thin strips of masking tape on the timing lines and paint the flywheel black. The next step is to drill the holes for the trigger pins located above. I drilled some test holes in scrap metal and found that a number 12 ( .189 inches) drill bit was a good size to start with. With one pin, it was too small and I should have re-drilled it with a # 11 (.191), the size of the pin. With the other pin, the hole was too big and I had to use a dab of JB Weld. Drill the holes 5/8 inch deep. The trigger pins come in a kit with one short one and one long one, TECUMSEH p/n 730201. I found instructions for installing in one of the kits, but not in the other two kits so they are shown below.

Now the hard part is done.

Task 3. Installing the Trigger Coil

The trigger coil mounting bracket is fastened on the two bosses shown in the introduction using two 1/4 NC screws, ½ inch long with lock washers. If needed, the holes can be adjusted using a 1/4 round file. If the flywheel has factory installed trigger pins, use the hole centered between the bosses for the trigger coil. If you installed the trigger pins as above, use the hole offset to the left for the trigger coil. Set the trigger coil close to the trigger pins and adjust as necessary to have the center of the trigger coil track the center of both trigger pins when you rotate the flywheel. Again, adjustment of the hole with a 1/4 round file as necessary. Set the gap between the tall trigger pin and the trigger coil to 11/64 inch for an initial setting by adding thick and thin 1/4 inch washers between the trigger coil and the mounting bracket. Feed the trigger coil wires thru the unused hole to keep them from rubbing on the flywheel. The final trigger coil adjustments will be made in Task 5 by shimming, changing the washers.

Task 4. Installing Automotive Parts

The main objective of this whole effort is to be able to replace failed SSI units with an ignition system that is available, affordable and simple enough for almost any one to install. The mid 1980 Chrysler ignition system seems to satisfy this objective best of all. It basically is an ignition coil like that used in battery powered point / condenser systems with a transistor switch that replaces the points. The transistor switch and associated electronics is in a box called a control module. A trigger coil connects to the control module to initiate the spark. The web site,

http://members.aol.com/pullingtractor/ignition.htm

has a wealth of information; the main difference here is the trigger coil specifically designed for the Tecumseh engines.

I used an ignition coil from a junked Carvan that requires an external resistor ( Wells CR107 , $3 )to limit the current draw. The Tecumseh 32080 or Kohler 231281 or Stens 460-048 coils ($30 ) already have the resister built in and should work fine. The control module I chose was a Wells CR109 because of the lowest cost, $16.

The trigger coil leads( yellow and Blue ) are connected to pins A and B of the Control Module. At this point, it does not matter which is which. The - of the ignition coil ( black ) is connected to pin D of the Control Module. The + ( red ) of the ignition coil is connected to both pin C of the control module and the + 12 volt battery thru a switch. For my coil, I needed a ballast resistor also.

I found some crimp connectors MOTOMITE 85456 which with a slight crimp fit the pins of the control module. The Control Module can be mounted in any cool place. And the ignition coil where convenient. The Control Module, coil and spark plug must be grounded.

The 12 Volt power source will vary from tractor to tractor, but must be present for both engine start and engine run. If there is a fuse coming off the plus side of the battery , it could be connected to a switch , ballast resistor if needed and the plus terminal of the ignition coil. If the engine has an external DELCO motor / generator and regulator, the regulator probably has a L or Load terminal used for lights and a starter solenoid. This would be a good source for the 12 Volt power. If a more modern key switch is used with positions for a start solenoid and Aux, it could be used with a pair of diodes, 20 Volts or higher and about 4 amps or greater, 1N5406.

Never connect to the "M" of a key switch because this only connects to ground in the off position and has no connection in the on position.

Task 5 Adjust and Test

We do a functional test and adjustment here before installing the blower housing, using the starter motor and fully charged battery to turn the engine. We want to do the adjustment at a high cranking RPM so the spark plug is removed, threads connected to a bare wire which is grounded and the a new spark plug connected to the ignition coil. The picture below shows a modified SSI Under flywheel with the trigger installed in the left hole but the procedures also apply to a SSI Above flywheel with factory installed trigger pins and the trigger coil installed in the hole centered with the mounting bracket holes. We painted timing marks on the flywheel for the timing light but now need an associated TDC line on the Blower Housing Baffle. If the flywheel is turned to line up the trigger coil with the trigger coil timing mark, this should be TDC. It is best to have the cylinder head off and zero the travel of the piston with a dial indicator. If needed, the trigger mounting hole can be adjusted with a 1/4 round file. The initial air gap between the trigger coil and the tall trigger pin can be set to 11/64 inch by changing the washer stack.

When you first apply power to the ignition, it usually gives off a spark; this is normal. Power up the ignition, crank the engine and observe the spark plug. If a spark is not present, check the new ignition wiring and /or add a washer from the stack to reduce the air gap. When you get a spark, set up an inductive timing light aimed at the trigger coil and see where the timing is. If the spark occurs as the tall trigger pin passes the trigger coil, the adjustment is good. If the spark occurs when the short trigger pin passes the trigger coil then the trigger coil is too close ( the engine may try to start with 17 of spark advance ) and a thin washer needs to be removed from the stack to increase the air gap.

IF you are not able to find a good adjustment doing the above, try reversing the trigger coil leads that are connected to the control module. The ignition will work either way, but I have observed a difference in timing ( about 5 degrees of retard ).

The above adjustment is very conservative. If you are not able to find a good adjustment doing the above, try cranking the engine at a lower speed by installing a spark plug to add compression. It is important that the spark fire off the tall trigger pin when starting and transition to the short trigger pin as the RPM increases.

When the trigger coil is adjusted, all bolts tightened and wires secured, install the blower housing, run the engine and check to timing. It should be advanced 17 deg when the engine is running. Lastly, reinstall the badge over the timing light window .

Note: There is a short 5/16 NF bolt that holds the blower housing on the right side. If a long bolt is put in its place, the bolt will hit the trigger pin. It would be a good idea to check this before installing the blower housing.

Appendix 1 Making the Trigger Coil:

I have templates, patterns and special tools to make the trigger, but am trying to provide enough information here for someone to make there own. The trigger bracket is made of folded galvanized sheet metal about 1 /16 thick. Since it is part of the magnetic path, it needs to be made of iron. The part that is vertical when installed has two 1/4 holes about 2 3/4 inches apart for mounting to the block and centered about 3/16 from the edge. Locate the midpoint between these holes and carry it up to the part that is horizontal when mounted. The hole for the trigger coil when one is using factory installed trigger pins is centered on this line about 3/16 from the edge. Locate one more hole 5/8 inch to the left for the trigger coil when the trigger pins are installed as above.

The mounting bolt is 1/4 NC 1 ½ inches long. With a Radio Shack Rear Earth magnet (64-1895) fastened to the top with JB Weld. If the magnet is installed slightly off center, the rotation of the bolt can be used to help align the magnet with the trigger pin. The bobbin is spooled 7/8 full with fine, 32 gage ( .0080 inch) wire or full with 28 gage ( .0126 inch) wire. The winding is protected and wires fastened with E-6000 Adhesive.

I have some materials and supplies and can provide a Trigger Coil for $25. Contact me, Ed Stoller at edstoller@earthlink.net if you need one.

Ralph Made His Own Trigger Coil

Appendix 2 Tractor Pulling Ideas:

The original design of these engines had fixed spark advance, not with standing the switch between the two fixed spark timings. Ideally, the optimum spark advance depends on RPM ( and engine load). I would guess that the 17 degrees of spark advance is targeted to a nominally high RPM like 2800. There are some that abuse these engines by running them above the rated 3600 RPM, like 4000 RPM. It stands to reason then, that one might want to optimize the spark timing at the highest RPM to get maximum power out of the engine. The ignition replacement above has a lot of latitude to adjust the timing.

One idea is to add a second trigger coil ahead of the one above and to have a user operated switch to kick in the added spark advance when it was wanted. The smallest increment of added advance would be limited by the physical size of the trigger coils. I have observed that the trigger coils I made ( or my late wife actually made on her sewing machine) are more sensitive than need be. This is evidenced by the fairly large air gap. I did remove some of the wire so the bobbin was only about 7/8 full. So there is some latitude in reducing the diameter of the bobbin at least where they would touch. Also, the placement of the lead wires could be tailored allow the coils to be closer together.

A second idea is to make the mounting bracket, that the trigger is mounted on, slotted so it could be dithered. I remember my uncle Fred had a Model T, or was it an A, that had a lever behind the steering wheel for this. I would want it to be spring loaded to the engine start position. A throttle / choke cable or such could be used to pull it to a advanced position.

Thirdly, the Control Module seemed to add about 5 degrees of retard on occasion. I think the trigger coil has a positive going pulse follower by a negative going pulse or a negative pulse followed by the positive depending on the way the trigger wires are connected. This could effect the advance characteristics of the module. Also, as RPM increases the trigger voltage would increase which might act like a built in tac. If anyone has the performance characteristics of the control module , I would appreciate some input.

Lastly, if one wanted to play with the timing for the replacement ignition above, you could use all thin washers on the trigger coil and adjust the air gap to the trigger pins while still keeping the starting spark slightly retarded.

Again, the details of the replacement are also available as a 11 page file in PDF format of about 1 mbits. It can be down loaded at http://home.fuse.net/stoller/SSI_Replacement.pdf .