How To Test A Coil On A 8n Ford Tractor

Testing the coil on a Ford 8N tractor is a crucial step in diagnosing ignition problems. The coil transforms the tractor's 6-volt electrical system into the high voltage necessary to create a spark at the spark plugs, igniting the fuel-air mixture. A faulty coil can result in a weak spark, no spark at all, or intermittent engine performance. This guide provides a step-by-step procedure for testing the coil on your Ford 8N tractor.

Safety Precautions

Before commencing any electrical work on your tractor, prioritize safety. Disconnect the battery's negative terminal to prevent accidental short circuits or electrical shocks. Ensure the tractor is in a well-ventilated area to avoid inhaling any fumes. Wear appropriate safety glasses and gloves.

Tools and Materials Required

Gather the necessary tools and materials to facilitate the testing process. This includes:

• Multimeter (capable of measuring resistance and voltage)
• Screwdrivers (flathead and Phillips head)
• Wrench set
• Clean rag
• Wiring diagram for the Ford 8N tractor (optional, but helpful)

Procedure

Step 1: Visual Inspection

Begin with a thorough visual inspection of the coil. Look for any signs of physical damage, such as cracks, swelling, or oil leaks. Check the coil's terminals for corrosion or loose connections. Clean the terminals with a clean rag if necessary. If any significant damage is evident, the coil likely needs replacement.

Step 2: Resistance Testing - Primary Circuit

The primary circuit of the coil is the low-voltage side, connected to the ignition switch and points. To test the primary resistance:

1. Set the multimeter to the Ohms (Ω) setting, typically in the range of 200Ω or less.
2. Disconnect the wires connected to the coil's two small terminals. These are typically marked "+" and "-".
3. Connect the multimeter's probes to the two small terminals.
4. Observe the resistance reading. A healthy coil should exhibit a low resistance value, typically between 1.2 and 1.7 ohms. Consult the tractor's service manual or specifications for the exact range.
5. A reading of 0 ohms indicates a short circuit within the primary winding, signifying a faulty coil. An infinite resistance reading (open circuit) also indicates a problem within the primary winding.

Step 3: Resistance Testing - Secondary Circuit

The secondary circuit is the high-voltage side of the coil, connected to the distributor. To test the secondary resistance:

1. Set the multimeter to a higher Ohms (Ω) setting, typically in the range of 20kΩ or 20,000Ω.
2. Connect one multimeter probe to one of the small terminals on the coil.
3. Connect the other multimeter probe to the high-tension output terminal (the center terminal where the distributor wire connects).
4. Observe the resistance reading. A healthy coil should exhibit a resistance value between 7,000 and 10,000 ohms. Consult the tractor's service manual or specifications for the exact range.
5. A reading of 0 ohms indicates a short circuit within the secondary winding, signifying a faulty coil. An infinite resistance reading (open circuit) also indicates a problem within the secondary winding.

Step 4: Voltage Test - Input Voltage

This test verifies that the coil is receiving the proper voltage from the ignition system. This test needs to be done with the ignition switch turned to the "on" position, but without the engine running.

1. Reconnect the wire that runs from the ignition switch to the "+" terminal on the coil.
2. Set the multimeter to the DC Voltage setting (typically 20V).
3. Connect the black (negative) multimeter probe to a good ground on the tractor chassis.
4. Connect the red (positive) multimeter probe to the "+" terminal on the coil.
5. Turn the ignition switch to the "on" position (do not start the engine).
6. Observe the voltage reading. You should see approximately 6 volts (or slightly less, depending on the battery's condition).
7. If you read 0 volts, there is a break in the circuit between the battery and the coil, such as a faulty ignition switch, a broken wire, or a bad connection.

Step 5: Spark Test

This test confirms that the coil can produce a high-voltage spark. Exercise extreme caution during this step as it involves high voltage.

1. Disconnect the high-tension wire from the distributor cap.
2. Hold the end of the high-tension wire approximately 1/4 inch (6mm) away from a clean, unpainted metal part of the engine block or chassis. Secure the wire with insulated pliers or a similar tool to avoid electrical shock.
3. Have someone crank the engine.
4. Observe if a strong, blue spark jumps from the high-tension wire to the engine block. A weak, orange spark, or no spark at all, indicates a faulty coil or other ignition system problems (such as faulty points or condenser).

Step 6: Inspecting the Condenser (Capacitor)

While not directly testing the coil, the condenser (also known as a capacitor) plays a critical role in the ignition system alongside the coil. A faulty condenser can prevent the coil from functioning properly. Inspect the condenser for any signs of physical damage, such as swelling or leakage. Replacement of the condenser is typically recommended when replacing the points, as it is a common source of ignition problems.

Interpreting Results

Based on the test results, you can determine the condition of the coil:

• Correct Resistance Values and Strong Spark: The coil is likely in good working condition.
• Incorrect Resistance Values (Short Circuit or Open Circuit): The coil is faulty and needs replacement.
• Correct Input Voltage but Weak or No Spark: The coil is likely faulty, or there may be other issues within the ignition system (such as faulty points or condenser).
• No Input Voltage: Investigate the wiring between the battery, ignition switch, and coil.

Practical Advice and Insights

When replacing a coil, it's advisable to replace the condenser (capacitor) simultaneously, as these components often work together and a failing condenser can shorten the life of a new coil.

Ensure the new coil is compatible with your Ford 8N tractor's 6-volt system. Using an incompatible coil can damage the ignition system.

If you're unsure about performing these tests or are uncomfortable working with electrical components, consult a qualified mechanic. It's better to seek professional help than risk damaging your tractor or causing injury.

Keep a log of any repairs or maintenance performed on your tractor, including the date and description of the work. This record can be valuable for future troubleshooting and maintenance.

Regularly inspect the wiring and connections in your tractor's electrical system. Clean and tighten any loose or corroded connections to prevent future problems.

By understanding the basics of coil testing and following these steps, you can effectively diagnose ignition problems on your Ford 8N tractor and ensure it runs smoothly for years to come.