Horizontally Opposed Aircraft Spark Plug Maintenance: Best Practices and Reference Guide

Welcome to Derringer Aerospace's Aircraft Spark Plug Maintenance Reference Page, designed to assist mechanics and aircraft owners with essential spark plug care, maintenance, and troubleshooting. This guide covers everything from spark plug gaps and torque specs to cleaning methods and best practices. Scan the QR code on your Derringer Spark Plug Tray to access this page anytime during maintenance.

Spark Plug Gap Recommendations

Proper spark plug gap is critical for optimal engine performance. Below are the gap recommendations for Lycoming, Continental, and Franklin engines:

Maintaining the correct gap ensures efficient combustion and prevents misfires or pre-ignition. Always check gaps during installation or servicing using a precision feeler gauge.

Spark Plug Torque Specifications

Correct torque prevents damage to threads and ensures a proper seal between the spark plug and cylinder head. Below are the torque specifications for each engine type:

Use a calibrated torque wrench with a six-point deep socket for accuracy, and avoid over-torqueing to prevent cylinder head damage.

Spark Plug Cross Reference Charts

Finding the right spark plug for your engine is essential for safe operation. Below is a quick reference chart for approved spark plugs:

For other engine models, consult your engine's parts catalog or Service Instruction documents.

Aircraft Spark Plug Best Practices

1. Inspect Regularly: Check spark plugs every 50–100 flight hours for wear, fouling, or damage.

2. Rotate Plugs: Swap top and bottom plugs during inspections to balance electrode wear.

3. Use New Gaskets: Always install new gaskets to ensure proper sealing.

4. Monitor Resistance: Replace plugs if resistance exceeds 5kΩ or if electrode wear is excessive.

Cylinder Firing Orders

Understanding firing orders helps ensure proper installation and troubleshooting during maintenance:

Always verify firing orders against your engine manual before installation.

Spark Plug Care

Proper care extends the life of your spark plugs:

1. Clean threads using a wire brush or approved cleaning tool—avoid abrasive materials that damage threads.

2. Apply copper-based anti-seize compound sparingly on threads (avoid graphite-based compounds).

3. Store removed plugs in a clean, dry location to prevent contamination.

Spark Plug Cleaning

Cleaning fouled spark plugs can restore performance:

1. Use an approved abrasive cleaner or media blaster designed for aviation spark plugs.

2. Avoid excessive cleaning that may remove protective coatings from electrodes.

3. Check gaps after cleaning and adjust as needed.

Spark Plug Dos and Don’ts

Dos:

✅ Use approved aviation spark plugs only (e.g., Champion or Tempest).
✅ Follow torque specifications precisely using calibrated tools.
✅ Replace damaged or excessively worn plugs immediately.

Don’ts:

❌ Never reuse old gaskets—always install new ones during maintenance.
❌ Avoid using automotive anti-seize compounds; use copper-based aviation-approved products only.
❌ Do not clean plugs excessively; it can damage electrodes.

Conclusion

Proper spark plug maintenance is vital for safe and efficient engine operation in aircraft. By following these guidelines, mechanics can ensure reliable performance while extending the life of their spark plugs across Lycoming, Continental, and Franklin engines. Bookmark this page for quick reference during inspections and installations, or scan the QR code on your Derringer Spark Plug Tray to access it anytime!