What is the spark plug gap on a Model T Ford?
The spark plug gap for most Model T Fords is typically about 0.025 inches (0.64 mm).
In practice, the exact gap can vary based on ignition setup, plug type, and engine condition. Early Model T engines used relatively low ignition energy, so restorers often start with the 0.025-inch baseline, while some modern plugs or alternative ignition configurations may tolerate or require a gap up to about 0.030 inches (0.76 mm).
Historical baseline for the Model T
Historically, Model T ignition systems operated with limited energy, making a small, precise gap important for reliable starting and smooth running. Below are commonly cited guidelines used by enthusiasts and restorers.
- Baseline gap commonly used in restorations: 0.025 in (0.64 mm).
- Possible range for certain modern plugs or higher-energy ignition: up to 0.030 in (0.76 mm).
- Smaller gaps for magneto-only or very low-energy setups: around 0.020–0.025 in (0.51–0.64 mm).
In practice, start with 0.025 in and adjust based on starting, idle quality, and overall engine performance. Always recheck after making changes to ensure consistency across all plugs.
Ignition systems and plug types
Model T engines could be equipped with coil, magneto, or battery ignition. The gap recommendation can shift slightly depending on the energy delivered to the spark and the type of spark plug used.
Coil vs magneto considerations
Coil ignition generally tolerates a touch more gap within the traditional range, while magneto systems—a source of lower peak energy—often benefit from staying near the lower end of the gap spectrum.
How to set the spark plug gap on a Model T
To set the gap properly, gather the right tools and follow careful, methodical steps. This helps ensure reliable ignition without overstraining the ignition system.
- Disconnect power and access the spark plugs, removing one plug at a time to avoid disturbing timing or misfiring.
- Inspect the plug for wear, fouling, or damage; replace if necessary with a plug compatible with Model T ignition.
- Measure the gap with a feeler gauge, aiming for 0.025 inches (0.64 mm) as the starting target.
- If adjustment is needed, gently bend the ground electrode or select a plug with the desired gap; avoid forcing or prying the center electrode.
- Reinstall the plug, torque to the appropriate specification, and repeat for all cylinders; then test the engine's starting and running behavior.
Note: If using modern replacement plugs, follow the manufacturer’s recommended gap for that specific plug while staying mindful of the Model T’s historical baseline. After installation, perform a road test to confirm smooth operation.
Summary
For most Model T Fords, the standard starting spark plug gap is about 0.025 inches (0.64 mm). The exact gap can vary with ignition type and plug design, so begin at the traditional baseline, test engine performance, and adjust within the commonly cited range (roughly 0.020–0.030 in or 0.51–0.76 mm) as needed to achieve reliable starting and smooth running.
What is the spark plug gap for a Model T Ford?
The recommended Model T spark plug gap is generally between 0.0250.0250.025 and 0.0320.0320.032 inches, with some users and setups using up to 0.0350.0350.035 inches. While the factory specification is 1/321 / 321/32 inch (or 0.031250.031250.03125 inches), Champion plugs recommend 0.0250.0250.025 inches. The best gap can be found through experimentation based on your specific engine's condition, coils, and whether it uses a magneto or battery.
This video demonstrates how to gap a spark plug correctly: 1mFixAnythingSaveMoneyYouTube · Jul 6, 2024
Recommended spark plug gaps
- Factory spec: 1/321 / 321/32 inch (0.031250.031250.03125 inches)
- Champion recommendation: 0.0250.0250.025 inches
- Commonly used range: 0.0250.0250.025 to 0.0320.0320.032 inches
- For higher compression or electronic coils: 0.0350.0350.035 inches may work well
How to find the best gap for your car
- Start with a mid-range gap: A good starting point is 0.0280.0280.028 to 0.0300.0300.030 inches.
- Experiment:
- If the engine runs rough or misfires, try closing the gap slightly (e.g., down to 0.0250.0250.025).
- If the engine is very reliable, a slightly wider gap (up to 0.0350.0350.035) may be suitable, especially with certain aftermarket ignition components.
- Consider your ignition system: The optimal gap can vary depending on whether you're running a stock magneto/coils or an upgraded electronic ignition system.
- Mark your plugs: Some owners suggest marking the front of the plug after setting a specific gap (like 0.0300.0300.030) and installing it with the mark toward the front of the engine.
What is the spark plug gap on a 1930 Ford Model A?
Spark plug gap for a standard compression Model A is . 035".
What is the spark plug gap for a 1979 Ironhead?
Spark Plugs - 79-85 Ironhead - . 030" Gap.
What is the correct spark plug gap for?
The gap setting is different for each vehicle but most are somewhere between 0.028" and . 060". Consult the owner's manual or Champion ® catalog to find the recommended setting for the vehicle you're working on.
