Revitalise Your Tecumseh: Ignition Upgrade Guide

Many owners of older machinery, particularly those powered by robust Tecumseh engines, often find themselves looking for ways to enhance reliability and performance. One common area for improvement is the ignition system. This guide delves into the intricacies of converting older Tecumseh ignition systems, typically Capacitance Discharge Ignitions (CDI) or Solid State Ignitions (SSI), to a more modern, battery-powered setup. While the original question of 'how many Tecumseh engines have been converted?' is difficult to quantify precisely, the wealth of information available and the DIY spirit of many engine enthusiasts suggest a significant number have undergone such upgrades for improved performance and ease of maintenance. This article will explore the various conversion methods, essential components, and troubleshooting tips to help you achieve a successful ignition overhaul.

Understanding the Need for Conversion

Older ignition systems, such as magnetos and early CDIs, often rely on the engine's rotation to generate their own power. This is achieved through magnets on the flywheel passing by a coil within the ignition module. The key switch, in these systems, typically earths the ignition to shut it off. The problem arises when attempting to integrate a modern, battery-powered replacement ignition. These new systems draw power from the battery and are controlled by interrupting that power supply. Simply connecting them to the existing magneto-style kill circuit is unsuitable. Therefore, specific wiring strategies are required to correctly power and control these newer ignition modules, ensuring they receive power when needed and are safely shut off.

Key Components for Conversion

Regardless of the specific conversion option chosen, several key components are fundamental to a successful upgrade:

• Replacement Ignition Module: This is the core of the new system, responsible for generating and timing the spark.
• Ignition Coil: This component steps up the voltage from the ignition module to a level sufficient to create a spark across the spark plug gap. It's crucial to note whether your chosen coil has an internal ballast resistor. If not, an external one will be necessary.
• Trigger Coil: This sensor, typically mounted near the flywheel, detects the position of specific pins or magnets on the flywheel to determine ignition timing.
• Wiring and Connectors: Appropriate gauge wires, bullet connectors, ring terminals, and potentially a diode wire harness are essential for making secure and reliable connections.

Wiring Conventions for Clarity

To avoid confusion during installation and troubleshooting, a standardized wire colour convention is highly recommended:

• Red/Orange: Indicates a +12 Volts DC power source.
• Black: Denotes -12 Volts DC and Ground connections.
• Yellow: Typically used for the Timing / Trigger Pulse signal from the trigger coil.
• Blue: Often used for the negative side of the ignition coil connection to the control module.

Ignition Switch Terminology

Understanding the different terminals on a typical ignition switch is vital. While variations exist, common labels include:

• A: Accessories – Provides power to auxiliary systems.
• I: Ignition – Powers the ignition system when the key is in the 'Run' or 'Ignition' position.
• R: Run or Regulator or Rectifier – Often associated with the running circuit or charging system.
• S: Start – Provides power specifically during the engine cranking phase.
• M: Magneto – Used in magneto ignition systems, often left unconnected in battery-powered conversions.
• G/Ground: Connection to earth.

Installation Option 1: Utilising the Existing Key Switch

This method aims to integrate the new ignition system with your tractor's original key switch. It's a popular choice for those who wish to maintain the original dashboard aesthetic.

The Challenge

The main hurdle here is that the original key switch is designed to ground the magneto/CDI ignition in the 'Off' position. The new system requires battery power in both the 'Start' and 'Run' positions. Connecting directly to the 'Run' terminal (often 'A' or 'L') might not provide power during starting, while connecting to the 'Start' terminal ('S') will lose power once the key is released to 'Run'.

The Solution: Diodes

To overcome this, diodes are employed. A diode allows current to flow in only one direction. By placing a diode in series with the connection to the 'S' terminal (preventing feedback to the starter circuit) and another in the 'Run' circuit, you can provide power to the new ignition in both key positions without interference. A pre-wired 'Diode Wire Harness' can simplify this process significantly, with wires clearly labelled for their respective connections.

Important Considerations for Option 1:

• The replacement ignition typically draws around 3 Amps; using 6 Amp diodes offers a good margin of reliability.
• A Peak Inverse Voltage (PIV) rating of 600 Volts for the diodes is more than adequate to handle any voltage spikes from the starter solenoid.
• Always disconnect the battery before making any connections.
• Ensure the trigger coil is correctly positioned and gapped (.015" is a common starting point) relative to the flywheel's trigger pins.
• Mount the ignition coil and control module in a cool, accessible location. Ground the control module case if mounted on plastic.
• Carefully splice into the 'S' and 'Run' (or 'A'/'L') wires from the key switch, incorporating the diodes as per the wiring harness instructions.
• Connect the output wires from the control module to the ignition coil and the trigger coil as specified.
• Before final assembly, perform spark tests by turning the key on and off, and by spinning the flywheel manually.

Installation Option 2: Adding a New Toggle Switch and Pilot Light

This option is ideal for equipment that doesn't have an original key switch, such as some welders or compressors. It offers a straightforward way to power the new ignition directly from the battery.

Simplicity and Safety

This setup involves a fuse, a new toggle switch, and a pilot light. The pilot light serves as a visual reminder to turn the ignition off, preventing unnecessary battery drain. A common power source is the 'always hot' post on the starter solenoid.

Installation Steps for Option 2:

1. Disconnect the negative battery terminal.
2. Drill holes for the toggle switch and pilot light on the dashboard or a suitable panel.
3. Install the switch and pilot light, ensuring the pilot light has a good ground connection (either to the chassis or a dedicated ground wire).
4. Connect the 'always hot' power source (e.g., starter solenoid terminal) through a 5 Amp fuse to the toggle switch.
5. From the toggle switch, route power to the positive terminal of the ignition coil, terminal C of the control module, and the pilot light.
6. Connect the yellow trigger wire from the trigger coil to terminal B on the control module.
7. Connect the blue wire from the control module (terminal D) to the negative terminal of the ignition coil.
8. Ensure the control module is properly grounded.
9. Perform spark tests as described in Option 1.

Installation Option 3: Replacing the Key Switch

For a completely integrated solution, replacing the old key switch with one designed for battery-powered ignitions is the most professional approach.

Choosing the Right Switch

It's crucial to select a key switch that provides power to the ignition system when in the 'Run' and 'Start' positions, rather than one that grounds out an existing ignition. The white wire from the 'I' (Ignition) terminal of the new switch is typically used to power both the control module (terminal C) and the ignition coil (+ terminal).

Key Steps for Option 3:

1. Disconnect the negative battery terminal.
2. Install the trigger coil and set the air gap.
3. Mount the ignition coil and control module.
4. Remove the old key switch and install the new one, paying close attention to the terminal markings on the back of both switches.
5. Connect the white wire from the new switch's 'I' terminal to power the control module (terminal C) and the ignition coil (+ terminal), often via spliced red wires.
6. Connect the yellow trigger wire to the control module (terminal B).
7. Connect the blue wire from the control module (terminal D) to the negative terminal of the ignition coil.
8. Perform spark tests as outlined previously.

Troubleshooting Common Issues

A systematic approach to troubleshooting can resolve most problems:

Spark Tests

The most basic test is to connect a grounded spark plug to the ignition coil. When power is applied and removed from the circuit (by toggling the switch), a spark should be visible. This confirms the basic functionality of the ignition coil and module.

Timing and Air Gap

The physical position of the trigger pins on the flywheel relative to the trigger coil dictates the spark timing. The air gap between the trigger coil and the flywheel pins controls the RPM at which the ignition timing advances.

• Increasing the air gap delays the spark advance to higher RPMs.
• Decreasing the air gap advances the spark at lower RPMs.

Use a timing light to observe the spark's timing relative to the flywheel pins at different engine speeds (cranking, no load, and under load). The tall trigger pin is typically associated with the initial (TDC) spark, while a shorter pin or a different magnet might trigger the advanced spark.

Voltage and Wire Checks

Use a multimeter to verify that you have approximately +12V DC at the ignition coil's positive terminal and the control module's positive input terminal when the ignition is switched on.

Common Wire Connections to Verify:

• Blue wire from Control Module Terminal D to the negative terminal of the Ignition Coil.
• Yellow wire from the Trigger Coil to Control Module Terminal B.
• Ensure a ballast resistor is correctly installed in series with the ignition coil if required. An overheating coil usually indicates a missing or incorrectly wired ballast resistor.

Grounding

Crucially, ensure the control module and all ground connections are clean, tight, and making good contact with the engine or chassis.

Trigger Coil Functionality

A multimeter with a diode test function can be used to check the trigger coil. With the trigger coil disconnected, test the resistance between its output wires. For many Tecumseh triggers, a resistance of 9-11 Ohms is expected. A diode test across the trigger wires (if a diode is incorporated internally or externally) should show a voltage drop in one direction and an open circuit in the other.

DIY Trigger Coil Options

For the truly adventurous, or for those needing to replace a damaged trigger coil, DIY options exist:

Modifying Existing SSI Modules (e.g., Tecumseh 610906)

Some older SSI modules contain a functional trigger coil. By carefully removing the epoxy potting, cutting specific traces on the circuit board, and adding a diode, the original trigger coil can be repurposed. This is a delicate process that requires precision to avoid damaging the coil.

Sewing Machine Bobbin Trigger

A surprisingly effective method involves winding magnet wire onto a sewing machine bobbin. By experimenting with the number of turns (around 400 is often cited) and the air gap, a functional trigger coil can be created. This often requires a diode in series with the output and careful attention to winding direction and magnet placement on a pole piece.

Materials for Bobbin Trigger

• Plastic sewing machine bobbins (Class 15 recommended)
• 30 AWG magnet wire
• Yellow or black stranded lead wire
• Small neodymium magnets
• 1/4"-20 bolt and nut for mounting
• E6000 adhesive
• Diode (e.g., 1N4005)
• Terminal strip

List of Potential Replacement Parts

When sourcing components, consider these part numbers and brands:

Ignition Coils:

• Tecumseh*: 32080
• Kohler*: 231281 or 237256 (NAPA 4151921S)
• Mopar: 4176009
• Ford/Motorcraft: D5TE-12029 (Note: "use with external resistor")
• STENS: 460-048

Ballast Resistors (if required):

• Wells: CR 107
• NAPA: ICR23

Ignition Switches (for Option 3):

• NAPA: 7-01854 (Ensure it powers the ignition, not grounds it)

Note on Ballast Resistors: If your replacement ignition coil does not have an internal ballast resistor, you must install one in series with the coil's positive terminal. Failure to do so will lead to premature coil failure, often indicated by overheating.

Conclusion

Upgrading the ignition system on a Tecumseh engine can significantly improve starting, running, and overall reliability. Whether you opt for integrating with the existing key switch, adding a new switch, or even undertaking a DIY trigger coil project, careful planning and execution are key. By understanding the principles of these battery-powered ignition systems and following the outlined installation and troubleshooting steps, you can successfully revitalise your Tecumseh-powered equipment and ensure it continues to serve you reliably for years to come.