Chainsaw engines are predominantly either 2-stroke or 4-stroke combustion engines that use gasoline as fuel. Combustion engines require a spark to ignite the fuel that is injected into the cylinder thereby activating the piston. The device that delivers this spark is called a spark plug and it looks like this:
TABLE OF CONTENTS:
- Do ALL chainsaws need spark plugs?
- How do spark plugs work?
- What kind of spark plug does a chainsaw take?
- When should a spark plug be replaced on a chainsaw?
- How do I know if my spark plugs need changing?
- Can you replace chainsaw spark plugs yourself?
- What happens if you don’t change your spark plugs?
- How much does it cost for a spark plug?
Do ALL chainsaws need spark plugs?
Gas-powered chainsaws rely on a fuel-dependant combustion engine which – in very simple terms – needs a spark to ignite the fuel to drive the piston which makes the chain move. A spark plug is the component that provides the spark and is absolutely essential in gas-powered chainsaws.
Other types of chainsaw such as electric or cordless (battery powered) don’t require fuel to run, therefore no spark plug is needed.
How do spark plugs work?
A spark plug is an electrical component that fits into the cylinder head of any combustion engine. When gasoline is sprayed into the combustion chamber the spark plug delivers an electrical spark which ignites an air/fuel mixture and the expanding gasses activate a piston. Depending on the size of the engine, this happens multiple times per second.
It works by chanelling an electric current from a battery through the electrode which is insulated with ceramic material. With nowhere else to go, the positive electric charge is then forced to ‘jump’ over to the grounded terminal at the end of the plug creating an arc of electricity (a spark).
On contact with the fuel/air mixture, the gasses ignite (combust) which forces the piston down to drive the engine.
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For a quick overview of how a 2-stroke chainsaw engine works, the following video from STIHL is great for those new to chainsaw engines:
What kind of spark plug does a chainsaw take?
Different models of chainsaw require slightly different spark plugs, and this will always be referenced in the user manual. Its always best to use the recommended plug for your specific model.
That said, brands such as NGK, Bosch and Champion offer spark plugs that are interchangeable for pretty much any chainsaw. As long as the dimensions and heat range are the same you should be good to go.
To identify the exact spark plug for your chainsaw, this Chainsaw Sparkplug Application Chart should point you in the right direction.
When should a spark plug be replaced on a chainsaw?
Many chainsaw manufacturers recommend changing out your spark plug after every 100 service hours. A spark plug is an essential part of any combustion engine, providing the means to ignite the fuel. If it’s corroded, overly worn or damaged, the engine will operate poorly if not at all.
To put it in perspective, someone who uses a chainsaw all day every day (for their job) will need to replace the spark plug every couple of weeks. While the occasional user may only need to replace it every few months, depending on useage of course.
How do I know if my spark plugs need changing?
If the spark plug has begun to deteriorate in any way, there will be some tell-tale signs during normal operation. A black carbon build up or oily residue on the end of the plug will affect the performance of the engine causing it to feel rough and laboured rather than a normal smooth operation.
If the engine is stalling regularly, this is another sign that the spark plug may be on its way out. The simple way to check the condition of the spark plug is to pop off the cable attached to the top of the plug and use a socket to unscrew it from the cylinder.
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In the image below, the left plug has some signs of wear but should still operate as required. The one on the right is fouled with oil and has black carbon deposits on the terminal which would definitely affect performance.
The wisest course of action is to change the spark plug regularly to ensure your chainsaw is operating in the most efficient way possible. Spark plugs are cheap! Regular change-out protects your engine from the stress of operating with inefficient spark plugs. It’s a no-brainer!
Can you replace chainsaw spark plugs yourself?
It’s as easy as unplugging the cable, unscrewing the old plug and replacing it with a shiny new one. Depending on the type of chainsaw you have, you may need to remove some casing or unscrew a panel or something, but it’s pretty straight forward. Here’s an example of changing the spark plug on a STIHL MS250:
What happens if you don’t change your spark plugs?
Without regular replacement of the spark plug, the performance of the engine will continue to decline causing starting issues, stalling and eventually the inability to function.
Prolonged use of a chainsaw with bad spark plugs makes it inefficient, difficult to use, can damage the engine and also negatively impact the environment. Spend a few bucks and buy a new one, Ebeneezer!
How much does it cost for a spark plug?
It’s like, under 10 bucks for a single spark plug. You can obviously pay more for higher performance ones but you dont need them. Just as an example, this Husqvarna one from Amazon is a typical plug for a wide range of chainsaws – under $7 at time of writing this article.
If your chainsaw is equipped with a gas-powered combustion engine, a spark plug is absolutely essential. Without a spark to ignite the air/fuel mix there is no combustion, therefore the engine will simply not start.
Other types of chainsaw such as electric or battery-powered versions don’t require fuel to run, therefore no spark plug is required.