Mower Maintenance: What to Do and When

Intervals are given in engine hours or in seasons, whichever comes first. A homeowner who mows an hour a week racks up far fewer hours than a commercial crew, so the seasonal trigger usually fires first. The manual still wins over every interval in the table.

On a zero-turn, the first hydraulic service falls around 50 to 100 hours, then roughly every 400 hours. On a new gas engine, the first oil change comes at 5 hours.

"Every 50 hours" means nothing without a count, so keep an hour meter or a simple log of when you mow and when you last serviced the machine.

Let the machine cool, then clear clippings from the deck, the discharge chute and the mulch plug. Empty and brush out the catcher, wipe the exterior, and check that the blades are sharp, straight and tight. Vibration loosens fasteners, handles and cables, so snug them as you go.

On a gas mower, turn the fuel valve off after mowing and top up the tank after the job rather than before: a full tank leaves less room for air and moisture.

Clippings left under the deck hold moisture, cause rust, block airflow and lead to clogging and an uneven cut. Some decks have a wash port; where you rinse, dry the deck afterward and touch up chipped paint.

Oil

Check the oil cold, on level ground, with the dipstick, before each use. Change it annually or every 50 hours, whichever comes first, and at 5 hours on a new engine. A push mower holds about 15 to 18 oz and a riding mower 48 to 64 oz.

Use SAE 30 in warm weather, 10W-30 where temperatures swing, and 5W-30 synthetic for cold starts. Pick a detergent oil rated for small engines and add no additives. Drain through the drain plug or tip the mower through the dipstick tube, and tip it only in the direction the manual specifies so oil doesn't soak the air filter and fuel doesn't flood the engine.

Air filter

Replace a paper element when it is dirty. Wash a foam element in warm soapy water, let it dry, and work in about two tablespoons of clean oil. Do this at least once a year, and every 25 hours in dusty conditions.

Spark plug

Replace the plug about once a year or every 100 hours, check the gap, and hand-start the threads before snugging it with a socket. Never cross-thread it.

Fuel filter

An in-line fuel filter is replaced annually or every 100 hours.

Fuel and ethanol

Gas goes stale in as little as 30 days. Ethanol above 10% attacks rubber parts such as fuel lines, primer bulbs and carburetor seals, and it is the usual cause of a mower that won't start in spring. Prefer ethanol-free fuel or add a stabilizer, store fuel in a sealed approved container out of sunlight, and for storage longer than a month run the tank and carburetor dry.

Cooling

Air-cooled engines need clean cooling fins and a clear air-intake screen, or they overheat.

A dull blade tears rather than cuts, leaving frayed, whitened tips that brown within a day or two, invite disease, cost more fuel and force extra passes. Sharpen every 20 to 25 hours of mowing, which for most homeowners is one to two times a season, and every 10 to 15 hours in sandy soil or thick warm-season grass. Sharpening at the start of the season, mid-season and late summer is a sound habit.

Watch for torn tips, uneven height, thin uncut strips, clumping, bogging down and unusual vibration. Those are the signs of a dull blade.

Removing and sharpening the blade

Disconnect the spark plug boot and ground the wire against the engine, or remove the battery key on an electric mower. Wear thick gloves and eye protection, brace the blade with a block of wood, and remove the bolt. Sharpen at the correct angle with a file or grinder without overheating the metal.

Balancing and reinstalling

Balance the blade on a cone balancer. An unbalanced blade wobbles, strains the bearings and cuts unevenly. Reinstall it with a torque wrench to the manual's spec.

When to replace instead

Replace rather than sharpen a blade that is bent, cracked, deeply nicked or worn thin, and after roughly five to ten sharpenings. Never straighten a bent blade with heat and never weld a cracked one, because blades can shatter. On multi-blade decks, replace blades and bolts in sets to keep the balance. A spare set swapped mid-season saves a trip to the shop.

The deck is where clippings, moisture and rust do their damage. Clean it after each mow, scraping with a putty knife or plastic scraper, never with your hands or feet, and never with the engine running.

A leaf blower or air compressor does the job without water. Where you hose the deck, dry it afterward and use a wash port if the deck has one. Touch up chipped paint and wax the deck so grass slides off.

A clean deck means better airflow, better discharge, less clogging and a longer-lived machine. A deck that keeps clogging usually points to wet grass, a dull blade or a dirty deck, so mow dry where you can.

A battery mower needs far less routine work than a gas one, with no oil, no plug and no fuel, but the battery is the expensive part and deserves care. Keep the battery and charger contacts clean and dry, since a corroded contact means a poor charge. Let the battery cool for about 15 minutes after mowing before charging.

Lithium-ion packs last longest when they are neither run flat nor left sitting at 100%. Recharge before they drop very low, and for off-season storage leave them at roughly half charge, in a cool, dry place, away from metal objects and out of freezing conditions. Don't store a pack at zero or at full for months.

Capacity fades over the years, and a pack that gives noticeably shorter runtime is due for replacement. Clean the deck and check the blade as on any mower.

A corded mower is the simplest machine to keep: no engine, no fuel, no oil. The maintenance is the cord and the blade.

Inspect the cord and plug for nicks and damage before each use, run an outdoor-rated extension cord on a GFCI-protected circuit, keep the cord out of the cutting path, and never mow wet grass. Keep the blade sharp and the deck clean as with any mower, and check that the handles, fasteners and switch are sound. Store the cord coiled and dry.

A robot is a maintenance mower, built to clip a little, often, and its upkeep is different again. Its blades are replaced, not sharpened: small razor blades on the cutting disc, changed roughly every three to six weeks in the growing season, always with the new screws that come with them. Never mix old and new blades on one disc, and reset the blade timer in the app. Replace them when grass tips look frayed or whitened.

Clean the chassis, wheels, skid plate and charging contacts regularly, by hand and brush, never with a pressure washer. Keep the charging station shaded, level and its contacts clean. On models with cameras and sensors, keep the lenses and windows clean and check the lift, tilt, rain and obstacle sensors periodically.

The battery typically lasts a few years. Store the mower charged, indoors and frost-free over winter, and keep the boundary wire intact.

A reel mower cuts like scissors, with reel blades against a stationary bedknife, and needs little but adjustment and oil. The adjustment is delicate: a sixteenth of a turn is a real change, and you loosen the opposing screw an equal amount before tightening one.

Verify with the paper check. Slip a sheet of newspaper between the cutter bar and the reel, turn the reel by hand, and every blade should slice it evenly across the full width. Adjust for light contact only, and never adjust a machine that has just been running hot.

Lubricate the reel axle, the gears and the wheel bearings so the reel spins freely. When it is properly adjusted and oiled, sharpening may not be needed for several years. When it is, back-lapping with a lapping compound is the do-it-yourself method and grinding is a shop job. Mow regularly, before the grass gets long, since a reel struggles with tall grass.

These carry everything a walk-behind does, plus a drivetrain. On top of oil, filters, plug and blades, check tire pressure, which sets cut height and traction, and inspect belts and pulleys for cracks and wear. Grease the fittings, caster wheel bearings and pivot points, check the deck level and blade height, clean the battery terminals, check lug-nut torque, and clear the cooling fins and air-intake screen.

On a zero-turn, the hydrostatic transaxles add hydraulic fluid and filter: an initial change in the first 50 to 100 hours, then roughly every 400 hours. Check the fluid only when the system is cool, and never change it without also changing the filter. Check the safety interlocks and never operate on slopes beyond the manual's limit.

A riding mower needs more oil, more filters and more blades than any walk-behind, so its annual upkeep is the highest of the group.

Spring checklist

• Fresh fuel and a new spark plug.
• Oil change and a clean or new air filter.
• Sharpen and balance the blade, and clean the deck.
• Check tire pressure, belts and fasteners.
• Charge the battery and clean its contacts.
• Check the cord on a corded machine.

Do all of it before the first cut.

Fall and storage checklist

This applies any time the mower will sit for a month or more, not just winter. Change the oil before storage so old acidic oil doesn't sit in the engine. Run the tank and carburetor dry, or fill with stabilized fuel and run it through. Clean the deck thoroughly and sharpen the blade so it is ready in spring.

• Charge the battery and disconnect the cables.
• On a battery mower, store the pack at about half charge, cool and dry.
• Store the machine dry, level, away from ignition sources and out of reach of children.
• For a robot, charge it fully, power it off and store it indoors and frost-free.

Booking a professional tune-up in fall or winter avoids the spring queue.

Won't start

Work through air, then spark, then fuel. Check that the air filter isn't clogged, that the spark plug isn't fouled and that the gap is right, then suspect fuel. Stale gas and a gummed carburetor from ethanol are the usual culprits after a winter sitting. Drain and refill with fresh or ethanol-free fuel; if it still won't run, the carburetor and fuel lines may need cleaning or replacing.

Runs rough or surges

A partially clogged carburetor jet or a dirty air filter is usually behind it.

Uneven cut or brown tips

Look at the blade first: dull, unbalanced or bent. Then check tire pressure, a deck clogged with clippings, and a deck that is out of level.

Deck clogging

Wet grass, a dull blade, a dirty deck or mowing too much at once all cause it.

Self-propel not working

Check the drive belt, the cable adjustment and the wheel gears.

A tune-up covers oil, plug, filters, blade sharpening, a carburetor clean, adjustments and an inspection. Handing it off makes sense for a zero-turn's hydraulics, a reel mower's grinding, or simply when you have no time or tools.

The price rises with the mower type and its complexity. A reel or push mower is the cheapest to service, a self-propelled more, a riding mower or lawn tractor more again, and a zero-turn the most. It also rises with whether the shop collects and returns the machine, with labor rates in your area, and with what is included: a basic oil-and-plug service costs less than a full tune with carburetor work, blade sharpening and adjustments.

The do-it-yourself tier is a few consumables and an afternoon. The professional tier buys the diagnosis and the jobs you can't do at home. Off-season booking is cheaper and faster than the spring rush.