A spark plug is the heartbeat of a chainsaw by providing the fire for the combustion of the chainsaw’s engine.
Without a correctly firing spark plug, a chainsaw will not run properly or maybe not run at all.Like any other component of the chainsaw, spark plugs wear out and need to be replaced from time to time. In order to replace a spark plug, you need a properly sized wrench or socket.
What size wrench do you need to replace your chainsaw’s spark plug?
When replacing the spark plug of a chainsaw the most common wrench sizes are 3/4 (19mm) and 5/8 (16mm). The least common wrench size for a chainsaw spark plug is 13/16 (21mm) and is usually present in older saws no longer in production.
Depending on the model of chainsaw your spark plug will require either a 3/4 (19mm) or a 5/8 (16mm) wrench.
The 3/4 (19mm) spark plug is significantly more common than the 5/8 (16mm) spark plug in chainsaws. A 13/16 (21mm) spark plug is very rare today and is mostly only used in extremely old out of production chainsaws.
Most chainsaws when purchased come with a properly sized spark plug wrench.
However, if you have lost yours, you can find spark plug wrenches at most major retailers.
PRO TIP: To cover all your bases you can purchase spark plug wrenches that have both 3/4 (19mm) on one end and 5/8 (16mm) on the other end. Buying a wrench of this type with both sizes will ensure you have the correct size for whatever chainsaw you are using at the time.
What Size Is A Chainsaw Spark Plug?
The most common size for a chainsaw spark plug is 3/4″ (19mm). There is a less common chainsaw spark plug variant that is 5/8″ (16mm).
What Size Wrench Do I Need To Remove A Spark Plug From My Chainsaw?
The size wrench needed to remove the most common chainsaw spark plug is 3/4″ (19mm). Some less common chainsaws use a 5/8 (16mm) wrench.
What Size Spark Plug Does A Husqvarna Chainsaw Use?
Modern Husquvarna chainsaws, like the Husquvarna 450, 455 and 460 most commonly use a 3/4″ (19mm) hex head spark plug like the NGK BPMR7A, NGK BPM6A, and the NGK BM7A.
NOTE: You will need to refer to your chainsaw’s owners manual or information from a trusted source about which exact spark plug your chainsaw needs. Using wrong spark plug in your chainsaw can damage your chainsaw’s engine or ignition coil.
Some older husquvarna chainsaws, like the Husquvarna A100, G90, and SM150 use a 13/16″ (21mm) hex head spark plug like the NGK B6HS and NGK BR6HS.
NOTE: As stated above you will need to refer to your chainsaw’s owners manual or information from a reputable source to make sure you get the correct spark plug for your chainsaw. The wrong spark plug can damage your chainsaw’s engine or ignition coil.
What Size Spark Plug Does A Stihl Chainsaw Use?
Stihl chainsaws use either a 3/4 (19mm) hex head spark plug or a 5/8 (16mm) hex head spark plug. The 3/4 (19mm) spark plug is more commonly used in Stihl chainsaws than the 5/8 (16mm) spark plug.
The NGK BPMR7A spark plug is the most popular 3/4 (19mm) used in Stihl chainsaws like the Stihl MS290, MS310, MS311, MS390 and MS391.
The NGK CMR6H spark plug is the least popular 5/8 (16mm) spark plug used in Stihl chainsaws like the Stihl MS171, MS181, MS193, MS194, MS211, MS241, MS251, MS362.
NOTE: You will need to refer to the owners manual of your chainsaw or information from a trusted source to ensure you get the correct spark plug for your Stihl chainsaw. The wrong spark plug can damage your chainsaw’s engine or ignition module.
How Often Should You Change The Spark Plug In A Chainsaw?
The life of a spark plug can last for years on a properly maintained chainsaw depending on usage level.
The spark plug of a chainsaw should be replaced every 100 hours of chainsaw operation or earlier if spark plug electrode damaged or fouled.
On chainsaws that are not properly maintained the spark plug can have a significantly shorter life span.
Factors that can contribute to a shorter spark plug life span include:
- Clogged Coolling Fins
- Improperly Mixed Fuel
- Clogged Air Filter
- Excessive Idling of Chainsaw
Clogged Cooling Fins
Clogged cooling fins can lead to engine overheating. When the cooling fins are clogged with dirt, they can not expel heat properly which leads to excess heat build up in the engine. Excess heat can damage a spark plug and other engine components like the cylinder and piston.
Improperly Mixed Fuel
Impropelry mixed fuel can lead to the premature failure of a spark plug. If the fuel mixture is too rich, meaning excess oil in fuel, the spark plug electrode will become coated with carbon and oil build up ultimately fouling the spark plug. If the oil mixture is too lean, meaning not enough oil in fuel, the engine will run lean causing excess heat build up in the engine. The excessive heat can ruin the spark plug and possibly the engine completely. Mixing fuel properly is vital to the life of a spark plug and chainsaw.
Clogged Air Filters
Clogged air filters can change the air fuel ration of a chainsaws engine shortening the life of a spark plug. Always make sure your chainsaw’s air filter is clean.
Excessive Idling of Chainsaw
Excessive Idling of a Chainsaw is not good for a chainsaw’s spark plug or muffler. When a chainsaw idles for extended periods of time the engine is not operating at its intended performance level. Idling can lead to carbon and oil deposit build up on the spark plug electrode and inside the muffler.
Dont let your chainsaw idle for extended periods of time, its not good for it.
Wrapping Up
The spark plug of a chainsaw will need to be changed from time to time in order to ensure peak chainsaw performance.
Changing a spark plug requires a properly sized wrench with sufficient length to reach the spark plug.
Most chainsaw spark plugs require a 3/4″ (19mm) or 5/8 (16mm) wrench.
Chainsaw spark plug wrenches typically have two separate wrench end sizes on the tool. The most common chainsaw wrenchs have either a 3/4″ (19mm) and 1/2 (13mm) or 3/4″ (19mm) and 5/8 (16mm).
If you do not have access to a chainsaw spark plug wrench a common deep socket and ratchet will work just as good.
Good luck with replacing your chainsaw’s spark plug and be safe out there.