How Important Is the Correct Spark Plug on a Lawn Mower?

Spark Plug's Function

• The spark plug contains a metal electrode tip. This tip sits about an inch into the cylinder block's combustion chamber. A high-tension lead wire connects the spark plug to the mower's ignition module. When the ignition module sends a high voltage spark up the wire, the spark plug converts the electrical charge into a high-voltage spark, which arcs across the gap on the electrode. This spark ignites the fuel in the combustion chamber, powering the piston and crankcase.

Why It's Important

• The spark plug, therefore, is an absolute requirement for the combustion process to even start at all. Each spark plug manufacturer designs different spark plugs to produce a different voltage charge. These charges will ignite the fuel at slightly different temperatures. The lawnmower companies manufacture their engines with these charges in mind. If the spark plug isn't the correct one, the charge will be either too high or too low, and the combustion process will degrade.

Dangers

• The real problem with using a different spark plug from the manufacturer's recommendation is difference between the intended voltage and the actual voltage in the combustion chamber. If the plug ignites the fuel at too high a temperature, the engine will start heating up, which eventually will damage the piston and the crankcase. Additionally, the added voltage can damage the electrical circuitry in some mowers, often requiring expensive repairs.

Checking the Plug

• Before starting your lawnmower, disconnect the rubber boot from the spark plug and use a deep-set socket wrench to remove the plug. After taking out the plug, identify the numbers along its ceramic portion. These numbers will tell the operator which model spark plug the mower requires. When checking the plug, always refer to the lawnmower's operator manual. If you can't find your manual, contact the manufacturer directly for spark plug specifications.