We used a Hyundai HYM51SPE electric start petrol mower to create this guide, but this process should apply to almost every petrol lawn mower, whether self-propelled or a hover mower.

Petrol Lawnmower Servicing Guide

Removing the Spark Plug

The first step is to remove the lawn mowers spark plug. The spark plug is required to produce an electrical spark which ignites the air and fuel inside your mower’s engine. You can find out exactly how this works in our petrol mower starting guide.

Locate the spark plug which should be found at the front of the mower, right at the front of the engine. If you can’t find it, consult your owner’s manual for further information.

Remove the HT cap by firmly pulling it off. This will allow you to remove the spark plug by placing a long reach spark plug wrench over the plug and turning it anti-clockwise. Be careful to keep your wrench straight to avoid putting strain on the ceramic insulator as they tend to be quite fragile.

Replacing the Air Filter

The next step is to replace your air filter. Your air filter should be replaced whenever it is visibly dirty which will vary depending on how often you mow your lawn. We find once a month to be adequate.

You will usually find the air filter towards the front of the engine on either side. If you’re struggling to locate it, it’s usually opposite to the side where your exhaust is located. To remove the air filter cover you will need to unclip it. Once done, you will be able to see the air filter where it can then be pulled out and replaced.

Be careful not to allow any leaves or debris to fall into the air intake.

Replacing the Cutting Blade

Next up is the cutting blade. To do this you’re going to have to carefully tip the lawnmower onto its side. Note that it is also possible to sharpen your mower blade if you would rather not replace it.

Always complete this step with the spark plug removed. This will prevent the mower from accidentally starting which could then cause the blade to rotate which would present significant danger.

To remove the blade, wear a pair of heavy duty gardening gloves. Undo the centre bolt with a suitable wrench by turning it anti-clockwise. Remove the old blade plate and set it to one side before then replacing it with the new blade plate. Ensure this bolt is tightened to the correct torque as stated in your mower’s instruction manual. For this petrol mower it is 40ft-lb.

Now would also be a good time to thoroughly clean the deck of your mower. Read our petrol lawn mower cleaning guide for more information.

Changing the Oil

To change your oil, first locate your dipstick which could be on the top, side or back of your lawnmower.

The easiest way to remove the old oil is via a syphoning syringe which will suck the oil out. Remove the dipstick and insert the syringe until it goes no further. From there you will have to pump the oil manually by pulling the syringe up. You will quickly start to see old oil leaving the dipstick tube through the syringe.

Once all of the old engine oil has been removed, you now need to replace it with new oil.

Be sure to use the correct oil as per your owner’s manual. Add the correct amount of oil via the filler cap and replace the dipstick once done.

Replacing the Spark Plug 

Finally, it’s time to insert a new spark plug. Insert the new spark plug into the spark plug hole and tighten it by hand until finger tight. Be careful not to cross thread the new plug as this can damage the threads in the spark plug hole. Once it’s tight, tighten it further with your socket and replace the HT cap.

Once you’ve completed these steps, you’re now ready to take your lawnmower out into your garden and give your lawn a trim.

Final Verdict

Servicing any petrol lawn mower needn’t be difficult. You can save yourself money by having a go yourself with this simple guide. If you have any trouble, be sure to consult your manual as it will provide you with the exact steps required for your model of lawn mower.

Looking for a new petrol lawn mower? Check out our petrol lawn mower reviews

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