Introduction: Tune Up Your Lawn Mower!

About: Hi, I'm Sam and I like to make things - check out some of my projects below. I worked for this site from 2014 - 2023 and have nothing but love for the Instructables community. Keep making great stuff!

Keeping your lawn mower in good maintenance year-to-year is pretty easy, and only requires a few basic steps.

Read on my friend, then get out there and tune up your lawn mower!

Step 1: Basic Supplies

There are some basic supplies you'll need to purchase, which are as follows:

  • New air filter
  • New spark plug
  • Engine oil

I recommend removing the air filter and spark plug as outlined in the following steps and taking them with you to the store when you buy news ones. This way you'll be sure to return home with the correct replacements.

Step 2: Replace Air Filter

The air filter is important to replace at least yearly, as it ensures that clean air enters the engine for smooth performance.

Look for a panel on the side of the mower engine that will most likely be held on by one or two screws.

Remove the screws and pull the panel out to reveal the air filter. Mine is a paper-style filter with a rubbery surround that rests in place in a cavity in the panel, which is squished firmly in place when the screw is installed.

The outer edges of the housing where the filter presses in were full of dirt and dry grass on mine. I used a small brush to clean all of this off before installing the new filter and replacing the cover. That's it.

Step 3: Remove Spark Plug

The spark plug may be located in different places depending on your lawn mower model.

However it will always be accessible and is easy to spot. Look for a rubber cable capped on the end of a white tube with a nut-looking thing on the inside where it meets the mower engine. The white thing is the spark plug.

Gently pull the cap of the plastic cable straight off of the spark plug (it will just pop off with a bit of pressure).

Use a spark plug socket (in all cases I've seen it is 13/16", but it could vary) to unscrew the spark plug and remove it from the engine.

Do not replace it at this point, though, as we're going to do some other maintenance first where it is safer to leave the spark plug out.

Step 4: Drain the Oil

Remove the oil cap (which will be marked "OIL") and tip the mower onto its side so the oil drains out into a catch pan of some kind.

Leave the mower on its side to continue draining, and move onto the next step.

Note: Most mowers do in fact have a drain plug. You can use it to drain the oil rather than tipping the mower as I have done here. The logic is that this will allow almost all of the used oil to drain out, and keep the oil from potentially draining into the carburetor and potentially fouling your new spark plug. Like most things, there are differing opinions on this.

I've never had any problem with the tip method, but depending on your preference and style of mower, using the drain plug is an option.

Step 5: Remove Blade

Sharpening your blade at least once a season will help the mower run smoothly, and lead to healthier grass (sharp blades cut cleanly, whereas dull blades smash and rip the grass blades which can increase the likelihood of disease).

Never attempt to remove the blade unless the spark plug is removed.

To remove the blade, you may need to place a block of wood or similar on the opposite of the blade in the direction you loosen the main bolt to hold the blade in place.

Use a large socket wrench with the correct size socket (5/8" in my case), and while standing on the block of wood, loosen the nut.

My blade was locked on pretty tight, so I had to use short length of pipe to extend the handle of my wrench to provide an extra bit of leverage to initially break it free.

Step 6: Sharpen the Blade

Lawnmower blades are made with very mild (soft) steel, and don't require a lot of effort to sharpen.

Also, they don't have to be super sharp.

Many people use the term "butterknife-sharp" to indicate the ideal sharpness. You can sharpen your blade with a flat file, an angle grinder, bench grinder, rotary tool like a Dremel, or even 150 grit sandpaper.

I'd used several different methods in the past, but now I just use an angle grinder because it's quick and easy.

The goal is simply to remove any nicks or dents, and end up with a straight edge that's about as sharp as a butter knife.

For me, I just try to match the angle of the existing bevel and remove last years layer of grime. Unless there are large dings, this is usually enough to put a sharp enough new edge onto the blade.

If there are substantial dings or dents you may need to grind the edge down flat, and then grind a new bevel.

If the blade has been bent, or has larger dings or dents that you aren't comfortable trying to fix, you can take it to a professional or just simply purchase a new blade. (New blades are pretty cheap and will generally take less time to acquire than having someone try to fix your old one.)

While the blade is off the mower, I also take the time to scrape off any layers of gunk so the blade stays relatively balanced.

It's important to have a balanced blade. In the case of a very unbalanced blade your mower may vibrate excessively and cause undue wear on the engine.

To see if your blade is balanced, simply hang it on a nail (pounded perpendicularly into a wall) through the center hole and see how it hangs. If it doesn't hang balanced, grind off some additional material from the heavier side until it does.

Step 7: Clean Under Mower Deck

With the blade off, I like to quickly clean out any gunk from the underside of the mower deck with a putty knife and a wire brush.

PRO TIP from several commenters: Spray the underside of the deck with nonstick cooking spray (like PAM) at least yearly, and rinse off the underside of the deck after every mowing. This will prevent a gunky buildup like you see on my mower. Excellent tip people, thank you!

Step 8: Re-install Blade

The blade is then re-installed in the mower. Stand on a block of wood or other suitable material to keep the blade from spinning, and tighten the nut back in place.

This nut needs to be on very tight. Use a large wrench, and perhaps even an extension made from a pipe as I am doing in this photo, and put your weight into it.

If you've got a torque wrench, you can follow the torque settings outlined in your owner's manual.

Step 9: Install New Spark Plug

Install the new spark plug by threading it in by hand until it can thread in no further. Use a wrench and the spark plug socket to tighten the plug an additional 1/8 to 1/4 turn.

Then fit the cable cap back over the end of the spark plug.

Step 10: Fill With Fresh Oil

A four-stroke engine like mine takes common SAE 30 motor oil. Make sure you refill into the oil reservoir and NOT the gas tank. That would be very bad!

I poured 3/4 of my 18 ounce bottle of oil into the reservoir, and waited about a minute for the oil to run down from the sides of fill pipe into the tank. This way I can get an accurate measurement of the oil level when I install and remove the dipstick/cap to check the level.

I was a little low, so I added about an ounce at a time and checked the level a couple of times until the level was indicating full on the dipstick. See note in photo 2 for details.

Step 11: Recycle the Used Oil

Put the used oil into a suitable bottle for recycling. Any auto parts store will take it free of charge.

Step 12: Miscellaneous

If you want your mower to look shiny and new, give it a wipe down with damp cloth.

Look for loose bolts on the wheels and handle assembly, and tighten if needed.

Look for any other signs of problems. On mine, the top end of the drive cable is cracked (see photo 2), however it still functions as needed. It is now on my watch list though, so if/when it breaks I won't be surprised by it!

The throttle cable should be adjusted if it is feeling loose. Refer to your owner's manual for this if needed, as the adjustment method may vary depending on your model of mower.

Step 13: A Few Final Thoughts

If you are proactive, you can repeat these steps during the mowing season if needed (if you're in an especially dusty place, for example).

When you put your mower away for the winter months, some people recommend draining out all the gas and attempting to start the mower a few times to flush the remaining gas out of the lines.

Alternately, you can fill mower tank with fresh gas and the appropriate amount of fuel stabilizer (like STA-BIL), and run the mower for a few minutes to circulate the stabilized fuel through the lines. This is actually what I do, and my mower has always started up perfectly with one pull each Spring.

Any remaining gas in my gas container in the fall I just put into my car to use up.

There are many opinions out there on mower maintenance. These tips are the basics of what I do each year, and my mower has been running smooth for several years.

If you have anything to add or think I've missed anything critical, please let me know in the comments. Thanks for taking a look!

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