Tune up a lawn mower

About this project

For a clean-cut lawn, keep a clean-running lawn mower. Give it a thorough going-over at the beginning of each mowing season, and you'll prolong its life and avoid costly repairs.

Level of difficulty
1 of out 5

No home improvement experience necessary for this project, but if you prefer you can hire a pro.hire a pro.

What you need for this project


Air filter
Gasoline
High-quality detergent oil
Leather work gloves
Metal file
Metal scraper
Oil collection pan
Plastic gasoline container
Protective eyewear
Screwdriver set
Socket set
Socket wrench
Spark plug
Spark plug gap guage
Torque wrench
Turkey baster
Wire brush, small
Wrench set

Get it done - step by step:

  • Step 1: Be safe

    Start by reading all safety information in your lawn mower's manual, especially about handling the blade and disconnecting the spark plug wire.

    Wear heavy leather gloves and protective eyewear as you work.

    Remove the spark plug wire. This important step prevents the lawn mower from starting accidentally during the tune-up.

  • Step 2: Drain old gasoline

    You should burn off or drain gas from your lawn mower at the end of the mowing season, but if you skipped it last fall, use a turkey baster to suck old fuel from the tank. You don't have to drain your gas if you added fuel stabilizer within the last six months.

    Deposit the gas in a container approved for gas storage and dispose of it according to local regulations.

  • Step 3: Sharpen or replace the blade

    Carefully tilt the lawn mower on its side with the fuel tank's fill hole facing up. Grasp the blade with a gloved hand to keep it from turning when you remove the blade bolt. Remove the bolt and washer, put them where you're sure to find them later and remove the blade.

    Inspect the blade and decide whether to sharpen it or replace it, following these guidelines:

    • If the blade is deeply chipped or cracked, replace it with a new blade.
    • If the blade is dull or has small chips, take your lawn mower to a local hardware store or service center to have it sharpened.
    • Sharpen the blade yourself if you have the know-how and tools.
    When reattaching the blade, follow the blade's torque specifications, which usually range from 35 to 40 ft. lbs. Use a torque wrench to achieve the proper spec for your lawn mower.

  • Step 4: Scrape the underside

    With the lawn mower still tilted onto its side, use a metal scraper or screwdriver to scrape off dirt and grass that have caked onto the underside.

  • Step 5: Change the spark plug

    Use a socket wrench to carefully remove your lawn mower's old spark plug. If there's debris around the spark plug hole, scrape it away with a small wire brush, taking care not to let any fall into the opening.

    If the new spark plug isn't pre-gapped, gap the space between the sparking pin and the bracket with a spark plug gap guage.

    Screw in and tighten the new spark plug by hand. Use the socket wrench to give the plug a quarter turn.

  • Step 6: Replace the air filter

    If your lawn mower has an air filter, you might need to replace it, particularly if you live in a dusty area.

    • If it's a cylinder, unscrew it and remove the filter.
    • If it's a box, you might need to use a screwdriver to dislodge the cover.

    Tap the filter on a hard surface to shake out dirt. If the filter is plugged or especially dirty, replace it with a new filter.

  • Step 7: Add gas and change the oil

    Fill the lawn mower's fuel tank with fresh gasoline.

    Reattach the spark plug wire and then run the mower for a few minutes to warm the oil so it flows faster.

    Turn the lawn mower off and detach the spark plug wire. Carefully tilt the lawn mower with the spark plug facing up.

    Place an approved oil collection pan under the dipstick and remove the dipstick. Drain the oil from the mower into the pan and then refill the tank with fresh oil of the type specified in your owner's manual.

    Return the lawn mower to its upright position and reconnect the spark plug. Dispose of the oil according to local regulations.

Get what you need

Maintenance Tasks

1. Aerate your lawn

Bring trampled areas of your lawn back to life with lawn aeration.

Time
1-2 hours for typical suburban lawn
Difficulty
Moderate
Frequency
Aerate lawns that are severely compacted or on heavy clay soil every year. Aerate looser soils once every two or three years. Sandy soils seldom need lawn aeration.
Where
All US
Overview

Lawn aeration allows oxygen to reach deeper into the soil, which encourages roots to grow. It's especially well suited to lawns growing in clay soil and those that receive a lot of foot traffic, which compacts the soil.

Aerate your lawn when it's actively growing so it recovers quickly — that's mid-spring or mid-fall in the northern US, and late spring or early fall for in the southern US.

Task Steps
  1. If the soil is dry, water it deeply and wait a day or two until it is moist, but not saturated. Dry soil is difficult to penetrate with an aerator.
  2. Adjust the aerator to make holes that are 3 to 5 inches deep.
  3. Run the aerator back and forth across the entire lawn.
  4. Make a second pass, at a 90-degree angle to your first pass.
  5. Continue until you have created approximately a dozen holes per square foot of lawn.

2. Control crabgrass in your lawn

The coarse leaves of crabgrass stand out in a lawn. While it's impossible to get rid of every weed, you can control crabgrass so it doesn't take over.

Time
1-2 hours for typical suburban lawn
Difficulty
Easy
Frequency
Twice a year, in spring and late summer
Where
All US
Overview

Most lawns are plagued with crabgrass (Digitaria spp.). Crabgrass is an annual weed — it grows each year from seed, not from roots that survive year after year. The best way to control crabgrass is to keep new seeds from germinating.

Task Steps
  1. Make sure what you have is crabgrass. Crabgrass is a low-growing grass that's lighter green and has wider blades than lawn grasses. Crabgrass is often a problem along sidewalks, driveways and on slopes.
  2. Apply a preemergence grass weed killer to infested areas when the soil warms to around 55 degrees F in spring — about the time dandelions start flowering. Reapply in late summer to control seeds set during the summer. Follow all precautions and directions on the label.
  3. Pull any crabgrass plants you see during the season, so they cannot produce seed.

3. Dethatch your lawn

Removing excess thatch helps keep your lawn healthy. Not every lawn needs to be dethatched, so check first.

Time
2-4 hours for a typical suburban lawn
Difficulty
Moderate
Frequency
Once a year, or less
Where
All US
Overview

Thatch is a spongy, tangled mat of partially decayed grass stems, leaves and roots that sits between the green part of the lawn and the soil. A thin thatch layer helps grass roots stay cool and moist during the dry, hot summer. But when thatch is more than 3/4 inch thick, it can weaken the lawn by blocking water, fertilizer and air from reaching the roots. It's also a breeding ground for lawn diseases and insects. How quickly thatch build up varies. Grasses grown in the South are more prone to thatch than those grown in the North. Over-fertilizing encourages thatch. Grass clippings do not cause thatch buildup — they break down quickly, adding nutrients to the soil.

The dethatching machine you need depends on how thick the thatch is:

  • If the thatch layer is between 3/4 but less than 2 inches, use a core aerator or core cultivator to pull plugs of soil and thatch from the lawn. The extra air below the soil surface encourages thatch-eating soil organisms. 
  • If the thatch layer is more than 2 inches thick, use a dethatching machine: hand thatch rakes are suitable for small lawns while power rakes or vertical mowers are best for medium to large areas.
  • You don't have to dethatch if the layer is less than 3/4inches thick.

Task Steps
  1. To check thickness of the thatch layer, use a garden spade to dig up a cross section of grass and soil. Measure the thatch layer — it's the mat of light-colored organic matter on the surface of the soil.
  2. To minimize damage to healthy grass, set the depth of the detacher so it tears and lifts the thatch without ripping into the soil.
  3. Run the dethatching machine across the lawn, following the machine's instructions.
  4. Rake the lifted thatch and remove it from the lawn. You can add it to your compost pile.

4. Edge your lawn

If your lawn is creeping over the sidewalk and into garden beds, edge the lawn now, before it gets out of hand.

Time
2-4 hours for a typical suburban lawn
Difficulty
Moderate
Frequency
Two to three times per summer. Grasses with aggressive runners, such as St Augustine and zoysia, require edging more often.
Where
All US
Overview

Over time, lawn grasses begin to creep onto adjoining paved areas and into garden beds. The goal when edging a lawn is to cut a very narrow trench between the lawn and the adjacent surface, resulting in a clean line.

Although you can get away with edging just once or twice during the lawn season, edging every 4 to 6 weeks keeps the job from becoming difficult.

How often you should edge the lawn depends on how fast it grows. Grasses with aggressive runners, such as St Augustine and zoysia, require more frequent edging. Fescues and buffalograss seldom require edging.

Task Steps
  1. Use a lawn edging tool to slice between the lawn and the paved area or garden bed. The slice doesn't need to be more than a few inches deep:
    • Half moon lawn edger or sharp spade: use your foot to push the blade into the ground and then rock it from side to side. Slide it a few inches sideways and repeat. Once you find a rhythm, the job goes quickly.
    • Rotary lawn edger: roll the star-shaped cutter back and forth along the edge. Keep the blade sharp so it doesn't get stuck.
    • Gas-powered lawn edger: follow directions in the owner’s manual. Keep the cutting edge from touching concrete
  2. Sweep up and remove all clippings and soil. Compost or dispose of the clippings properly.