How to clean a lawnmower sparkplug

Approx Reading Time: 10 minutes

A sparkplug is one of the essential parts of the ignition system of a lawnmower. A well-working sparkplug is necessary for a good start of the engine and its smooth running. If you think your lawnmower has a defective sparkplug, changing or replacing it is not always necessary. Whenever a lousy sparkplug is diagnosed, and no physical damage is present on insulation, cleaning the sparkplug is the first thing you should try. Learning to clean the sparkplug is also necessary for your regular checkup and maintenance of the mower.

How to clean a sparkplug

  • Step 1: Remove the sparkplug wire
  • Step 2: Remove the sparkplug
  • Step 3: Give the sparkplug a visual check
  • Step 4: Clean the electrodes
  • Step 5: Use a Digital multimeter to check continuity
  • Step 6: Check the leaks of current using DMM
  • Step 7: Check the resistance range if the sparkplug has a resistor
  • Step 8: Clean the sparkplug connector points and wire ends
  • Step 9: Reinstall the sparkplug
How to clean a lawnmower sparkplug 1

Reason for the required spark plug cleaning

As suggested by the name, a spark plug is a device that produces spark inside the combustion chamber of an engine to start the combustion process. There can be various reasons for cleaning a spark plug. Before getting into more details of malfunction reasons, it is vital to look at the spark plug’s working.

● How a Spark Plug Works

The spark plug has a tip with no insulation covering on both heads. When a high voltage current passes through the spark plug, the small gap between the two head terminals allows the current to jump and produce a spark. The high voltage current is received from the ignition coil, which steps up the battery’s 12V current. In spark-ignition engines, the spark plug is an essential component. Without a sparkplug, the machine will not start. Due to this, although it is a small part, the importance is very high.

● Reasons for cleaning a spark plug

As we have come to know why sparkplug is such an essential component of a lawnmower, here are the reasons for the necessary spark plug change.

  • Engine health: With a lousy sparkplug, the engine health is reduced as it results in misfiring inside the engine affecting the cylinders badly.
  • Build upon Spark heads: Air flows in the engine cylinders at high speeds. Sometimes debris of dirt and oil also gets inside the cylinder. Spark plug being directly interacting components become clogged with these contaminants.
  • Wear and Tear: All components of a running machine need replacement and so do spark plugs. The lifetime of a spark plug varies from 25 – 30 running hours.

The spark plug needs cleaning for the lawnmower to work at its best and have an extended life. Scheduled maintenance might be a popular reason for spark plug cleaning.

Effects of the faulty spark plug

Knowing the effects of a faulty spark plug is essential to identify the symptoms for the necessary cleansing.

  • High fuel consumption: Who does not like their lawnmower to spend as less of gas as it can. Well, if the sparkplug is dirty engine loses its efficiency.
  • The engine will not start: as the sparkplug is not working, the cycle of a machine can never run, and hence engine would not start
  • Erratic operation: The engine, if it does start, feels very heavy and tends to run very irregularly.
  • Misfiring: This effect is not solidly observable, but all others are generally the aftereffect of this. Engine stroke timing suffers, and power losses are massive.

You might want to know more about the complete working cycle of a spark-ignition internal combustion engine with curiosity building. More knowledge will also help you understand more technicalities to help to detail, maintaining, and repairing. If technical details still do not interest you as much, you can skip to the next portion, where a step by step instruction for cleaning a spark plug is discussed.

In this next portion, the working of Spark-ignition engine and the construction of a sparkplug is discussed.

● A Spark Ignition Engine

A spark-ignition engine is an engine that operates on gas and is used in a lot of lawnmowers. If it is a diesel engine, you are in the wrong place as diesel engines are compression ignition engines and do not have a spark plug.

The term spark-ignition internal combustion engine can be reduced to parts to explain it.

  • Spark means the jump of current from one electrode of the sparkplug to the other with air as a medium to travel
  • Ignition means the start of the combustion process of the air-fuel mixture
  • Internal means processes take place in an enclosed space
  • Combustion means the burning of fuel that generates power to drive the rotary power

The engine converts the chemical energy of fuel into mechanical strength of the crankshaft. The operating cycle is the Otto cycle, which has four processes going on.

  • Intake of the air-fuel mixture
  • Compression of the mixture
  • A spark from the sparkplug
  • Combustion of fuel
  • Power stroke on piston head driving it down
  • The exhaust of burnt gases

The piston moves linearly and transfers power as rotational energy via a connecting rod.

● The detailed construction of a sparkplug

Here all the different components of sparkplug will be discussed.

  • Central electrode: The central electrode conducting current from the ignition coil and is present throughout the center of the sparkplug
  • Ground electrode: The side-mounted electrode that conducts the spark back to the ground
  • Electrode gap: Present between both electrodes through which high voltage current jumps and generates the spark
  • Copper core: Deeply inserted in the center electrode for better heat conductivity providing a complete range plug that works well at both high and low speeds
  • Resistor: Present in models with an” R” in their label and provides resistance to the high voltage current to save the electrode from blowing up
  • Gasket: Ensure the pressure is sealed inside the engine cylinder
  • Metal shell: Zinc-plated and chromated to guard against corrosion
  • Insulator: Made of high purity alumina, providing high electrical insulation, better heat dissipation, and stronger thermal shock resistance
  • Special packing: Excellent air tightness and robust construction
  • Part number: Imprinted on the ceramic portion of all sparkplug might vary from manufacturer to manufacturer for the same type of plug
  • Corrugations: To prevent the flashover. Flashover is the conductance of high voltage current directly to the ground instead of producing a spark through the gap
  • Terminal: The point where the sparkplug wire is connected that allows the current from the ignition coil to the sparkplug

Step by Step guide to clean a lawnmower sparkplug

● Step 1: Remove the sparkplug wire

After locating the plug, removal of the plug wire is performed. The wire can be pulled off using hands. It is preferred to use a sparkplug wire puller, ensuring the insulation does not get damaged.

● Step 2: Remove the sparkplug

If you want to remove the sparkplug, either a socket wrench or a sparkplug wrench tool can be used. The specialized tool has an extended neck of the socket and makes the job much more comfortable. Follow these stepwise instructions

  • Fit the wrench in place: Connect the wrench to the base of the plug
  • Loosen and unscrew the plug: Apply firm force to loosen up the sparkplug and then unscrew with ease with normal hand force
  • Removing old sparkplug: When unthreaded completely move the old sparkplug out

● Step 3: Give the sparkplug a visual check

Three things can be checked visually in a sparkplug

  • Ceramic insulation: check if there are any cracks in the white ceramic part of the sparkplug. If it is damaged, then most probably the plug is useless as it will be flashing over
  • Electrodes: check whether both of the electrodes are still present because sometimes they might blow up. In this case, it is a wise decision to throw it away.
  • Terminal: Check for any carbon deposits on the terminal side. It is sporadic to occur but easily observable.

● Step 4: Clean the electrodes if they are carburized

If there are carbon deposits on the electrode surface, it is better to clean them first to observe the best checking readings.

  • Step 1: Use a soft wire brush
  • Step 2: Brush through the neck thread and sides first
  • Step 3: At last, give a gentle brush to the electrode
  • Step 4: It is advisable not to use any abrasive methods like sanding or grinding as it will cause permanent damage to the plugs
  • Step 5: If the carbon deposits are very rock-solid, try spraying them with a cleaner such as WD-40.
  • Step 6: Again, brush the electrodes and the surroundings gently

● Step 5: Use a Digital multimeter to check continuity

  • Step 1: Set the DMM in the current mode
  • Step 2: Touch the probes together to check for proper functioning
  • Step 3: Put the sparkplug on an insulator surface (wood or cloth) and not on a metal vise or floor
  • Step 4: Touch one probe to the tip of the central electrode and the other to the terminal
  • Step 5: The DMM should give a beep and offer a 0 reading
  • Step 6: It shows that the central electrode is not broken 

● Step 6: Check the leaks of current using DMM

  • Step 1: Now instead of touching the other probe to the central electrode, connect it to the ground electrode
  • Step 2: The open-loop error should be visible
  • Step 3: Touch the probe on the gasket, insulation, and hex nut
  • Step 4: All should have an open-loop
  • Step 5: If the current conducts, the sparkplug is bad

● Step 7: Check the resistance range if the sparkplug has a resistor

If the spark has a resistor, It will have a letter R in the imprinted code. Instead of zero reading, a value of resistance will be observed. If this resistance is from 4-7 ohm, the sparkplug is okay. If higher or lower reading is followed, the sparkplug is terrible. Some plugs have a regular reading of 9 ohms, but in that case, it is generally mentioned as the last digit in code, i.e., 9.

● Step 8: Clean the sparkplug connector points and wire ends

  • Soft wire brush: Use a soft wire brush to clean the terminal on the sparkplug and the cylinder head connection point
  • Sandpaper: Use sandpaper of finer grade to remove any carbon deposits present on the wire connections.

● Step 9: Reinstall the sparkplug

  • Mind the electrode gap: Before reinstalling the sparkplug, it is imperative to gap it. Using the gap gauge or feeler gauge, choose the specific gap dimension a push between the electrodes.
  • Place the sparkplug in place: After gaping is completed, gently screw the new plug into the initial thread. Be as gentle as possible so that threads are not damaged.
  • Tighten the sparkplug: Screw with hand force and tighten using a wrench tool. Make sure not to overtighten because it might damage the plug, its seal, and threads

Related questions

1. Even all connections are made, and the sparkplug is changed, a bit of irregular behavior persists. Why?

This issue might be due to the sparkplug wire. Check the resistance using a multimeter; if higher than standard, replace the wire.

2. What to do to make sure the spark plug does not stick when changing next time?

Using an anti-seize compound around the thread of the sparkplug before threading is essential.

Final Remarks

Sparkplug is an essential component for the machine to start. Knowing how it works and what parameters are to test it for its performance are discussed here. Every lawnmower owner or any garden equipment should have detailed knowledge of sparking and sparkplug condition testing along-with the all-important cleaning procedure of sparkplugs.