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How To Service A Petrol Lawnmower

Petrol lawn mowers can require a fair amount of maintenance to make sure that they continue to work year after year. Ideally you should look to give your trusty machine a tune up after every 25 hours of mowing or at the end of each season. Spending time maintaining your machine not only can prolong its life but can also improve the efficiency of your lawn mower for when you need it the most. To make things easier, we’ve created the top ten things you will need to check when preparing your machine for the next grass cutting season.

1. Read the manufacturer's manual

Perhaps unsurprisingly, this should be the first port of call. Each lawn mower has different intricacies that require different care. The manual can help guide you through what is required in terms of maintenance with bespoke instructions for your machine in addition to any replacement parts when required.

2. Spark plugs

Spark plugs are the component that ignites the fuel in the engine, which in turn makes the blades spin. They are therefore an important part in the whole lawn mowing operation! Before you undertake any maintenance work however, it is important from a safety perspective to disconnect the spark plugs.

You will be working on the blades so, by disconnecting the plugs you ensure the mower cannot accidentally start. Once they are disconnected you can complete the rest of your work safely. Once all other maintenance has been finished you should clean or replace the spark plugs before reconnecting.

3. Drain all petrol

At the end of each mowing season it is important to either run the machine dry or to drain off any residual petrol. Typically petrol can have a shelf life of around 30 days and can go stale after a while. Therefore leaving it in the machine over the Winter is not advised. Trying to start the engine with stale fuel can also be very difficult and can damage the engine.  

If you are disposing of old petrol you will need to make sure you are disposing of it in the right way. Be sure to check with your local authority for advice on how and where it needs to be disposed.

4. Clean out any debris

Once it is safe to do so you will need to check underneath the cutting deck to make sure there is no trapped debris that could clog up your lawn mower. If you don't clean out the grass from around the air inlets or motor it can cause the machine to overheat, which can cause it to break down. Be sure to check your manufacturer’s instructions before you do this as some lawn mowers cannot be tipped on their sides. Residual fuel or oil can leak into the engine on some machines so double check beforehand what the recommended course of action is. Cleaning out the debris is much easier when you have just finished mowing, as the grass is still moist and can then be brushed off quite easily. Take care around the blades, as they are likely to still be sharp, ideally wear protective gloves if possible.

M46-125 Classic+

5. Tighten any loose bolts and wheels

This is a good time to check the different bolts on the machine to make sure they are all tight. It is a simple check but can have large benefits ahead of a new season. If any bolts are loose and fall off this can cause some serious problems with your lawn mower so better safe than sorry.

This goes especially for the wheels as they are going to be bearing the brunt of your work. You will need to make sure they are tightly screwed in and that they don’t have any issues. Lawn mowers can wobble a little, however if the movement is more significant it could be an issue with the axle nut, which may either need adjusting or replacing. It can also be an issue with the wheel itself, which can become unstable, compromising the look of your lawn.

6. Air filters

A lawn mower’s air filter will keep dust and debris from getting into your engine so is a vital part of the machine. This filter should ideally be replaced every three months or so to keep it running smoothly. Make sure you check the manufacturer’s instructions as, while air filters can all look similar, they can have crucial differences that are tailored to that specific engine.

When you remove the old air filter make sure you clean out the housing for the air filter. The last thing you will want is the machine to collect any remaining debris.

7. Replace the blade

This is important as blunt lawn mower blades can stress you grass. Instead of a clean cut, the grass is torn and won’t heal as quickly. Over time the blades in your lawn mower can wear out which makes them less efficient.

Whether your blades just need sharpening as opposed to replacing, depends on your mowing situation; such as size of lawn and how often you mow. Mower blades can be sharpened often before they need replacing but if you do need to replace your blades make sure to check with your manufacturer which blade is correct for your lawn mower.

8. Check pull starter cord

Starter cords go through a lot of work; the sharp repeated tugs could cause a lot of stress so it isn’t uncommon for the cords to become frayed or even snap. Replacing this before any serious issues occur can often be an advisable option rather than let it snap later on.

It isn’t necessarily a large job either as you will only need to remove the housing, then the old cord within the pulley system and replace with a new starter cord. Be sure not to turn the pulley itself when you are installing the new cord, as you want the springs to be undisturbed when the cord isn’t needed. Wrap the new cord around the pulley a few times without spinning the pulley then give it a test to see how it works. It should recoil quickly into the housing.

9. Changing the oil

You will need to consult your manufacturer’s manual for this as the plugs can be in different places. Be sure you have a pan to catch the draining oil before you remove the plug. You will also need to be sure that you are disposing of the oil in the correct manner. There are often waste or recycling centres that can accept old oil so make sure you dispose of it in the right way. Simply pouring it down the drain counts as pollution, which is breaking the law and can lead to prosecution.

Once you have removed the old oil you will need to replace it with high quality oil. It is best to use a funnel to prevent spills and never exceed the manufacturer’s instructions. Once all of the oil is in the engine it is best to quickly check with the dipstick to make sure the oil level is correct. Using high quality oil ensures the engine stays well lubricated.

10. Replace with new fuel before starting again

As you have removed old petrol at the end of the previous season it is therefore important to put fresh petrol in just before you start working. The lawn mower will, obviously, need petrol to function so be sure to purchase fresh petrol as close to the day you start mowing as possible so you can get the most out of it.