Lawn mower maintenance

A few checks before you pull the cord or turn the key catch most of the trouble small engines run into. Check the engine oil level first: on most push mowers, this means pulling the dipstick (a thin rod threaded into the oil fill, sometimes built into the oil cap itself), wiping it clean, reinserting it fully, then pulling it out again to read the level against the marks near the tip. Do this with the mower on level ground and the engine cold. Riding mowers work the same way, just with the dipstick usually located lower on the engine block. Low oil is one of the most common reasons a small engine seizes, since these engines hold far less oil than a car and have very little margin for running low.

Fuel matters more for small engines than most people expect. Gasoline with up to 10 percent ethanol, labeled E10, is generally fine for small engines built in 1995 or later, but fuel blends above E10 can damage rubber fuel lines, gaskets, and carburetor components not designed for higher ethanol content, according to guidance from the Outdoor Power Equipment Institute. Ethanol fuel also absorbs moisture from the air and breaks down faster than non-ethanol gas, so use fresh fuel, ideally bought within the last 30 days, and avoid letting a full or partial tank sit for months without a stabilizer.

Blade condition affects both cut quality and safety. With the spark plug wire disconnected or the key removed (never work under the deck with either connected), tip the mower and look at the blade's edge and overall shape. A sharp blade cuts grass cleanly; a dull or nicked one tears it, leaving ragged brown tips within a day or two. Also check that the blade isn't bent or cracked, since a damaged blade can fail during operation.

Finally, clear the deck, the housing underneath the mower that surrounds the blade, of any built-up grass clippings, dirt, or debris before you start. A packed deck blocks airflow, which reduces cutting performance and can cause the engine to work harder than it needs to.

Before you mow checklist

• Oil: dipstick check cold, level ground, before every use on both push and riding mowers. Low oil is a common cause of small-engine seizure, don't skip this.
• Fuel: E10 (10 percent ethanol) or less, per OPEI and manufacturer guidance; avoid higher ethanol blends unless the engine is explicitly rated for them. Use fuel bought within about 30 days; don't let stale fuel sit in the tank.
• Blades: disconnect spark plug wire or remove key before inspecting. Check for sharpness, nicks, cracks, and bends before each mow; replace anything visibly damaged rather than running it.
• Deck: clear clippings and debris before starting; a packed deck restricts airflow and cutting performance.

A handful of items need attention every few weeks of regular mowing rather than every single use. The air filter, which keeps dust and grass debris out of the engine's intake, comes in two common types: foam, which can be washed in warm soapy water, squeezed dry, and lightly re-oiled per the manufacturer's instructions, or paper, which is generally replace-only since washing damages the paper element. Check it every 25 hours of use or once a season, whichever comes first, and more often if you mow in dusty conditions, per Briggs & Stratton's maintenance guidance. Hold a paper filter up to the light; if you can't see light through it clearly, it needs replacing.

If your mower uses belts, drive belts (which turn the wheels on self-propelled models) or blade belts (which spin the cutting deck), inspect them for cracking, glazing (a shiny, hardened surface that reduces grip), or fraying. A worn belt can slip, causing reduced power to the wheels or blade, and eventually breaks without warning.

Deep-cleaning the underside of the deck goes beyond just clearing loose clippings. Built-up grass residue can harden into a caked layer that affects blade balance and airflow over time. With the spark plug disconnected, scrape and hose off the underside periodically, ideally after each mow if grass is wet or heavy, or at minimum every few weeks during the season.

Riding mowers add one more check that push mowers skip: tire pressure. Underinflated tires on a riding mower can cause uneven cutting height across the deck's width, since the deck's height relative to the ground shifts if one tire is softer than the others. Check pressure against the number in your owner's manual, typically in the 10 to 14 psi range depending on the model, using a standard tire gauge.

Periodic service checklist

• Air filter: inspect every 25 hours or seasonally per Briggs & Stratton, sooner in dusty conditions. Foam: wash, dry, re-oil per spec. Paper: replace, don't wash. Hold to light to judge paper filter clogging.
• Belts: inspect drive and blade belts for cracking, glazing, and fraying at each periodic service; replace before they fail rather than after.
• Deck: deep-clean underside every few weeks during season or after wet or heavy mowing, spark plug disconnected. Caked residue affects blade balance and airflow.
• Tires (riding mowers): check pressure per owner's manual spec (commonly 10 to 14 psi), uneven pressure causes uneven cut height across the deck.

Blades wear down gradually even with regular light sharpening, and eventually need full replacement or a professional sharpening and balancing job rather than a quick touch-up with a file. A professional sharpening service also balances the blade, meaning it checks that neither side is heavier than the other after metal has been removed from sharpening; an unbalanced blade vibrates the mower, which stresses the engine's crankshaft bearing over time. Plan on this once a year for regular use, more often if you mow rocky or debris-heavy terrain that dings the blade edge.

A full annual tune-up by a small-engine technician is worth scheduling even if you handle basic maintenance yourself. A technician checks things that are easy to overlook: carburetor condition and adjustment, valve clearance on engines old enough to need it, the condition of the muffler and spark arrester (a screen that traps sparks from the exhaust to reduce fire risk), and overall engine compression, an indicator of internal wear that isn't visible from outside.

Annual blade service checklist

• Blade replacement or professional sharpen and balance: annually for regular use, more often with rocky or debris-heavy terrain. Balance after sharpening; an unbalanced blade vibrates the deck and stresses the crankshaft.
• Annual technician tune-up: carburetor check and adjustment, valve clearance check on applicable engines, muffler and spark arrester screen condition, compression check. Worth scheduling annually even for owners who do their own routine service.

A handful of tasks are best handled at the boundaries of mowing season, either heading into storage in fall or waking the mower up in spring. Change the engine oil at least once a season, or every 50 hours of use for push mowers and every 100 hours for riding mowers, whichever comes first, per Briggs & Stratton's guidance. Drain while the engine is still slightly warm, since oil flows more easily and carries more contaminants out with it.

Replace the spark plug, the small component that ignites the fuel and air mixture inside the cylinder, once a season or every 25 to 100 hours depending on your model, checking your manual for the exact interval and gap. A worn plug causes hard starting and rough running. Set the gap, the small space between the plug's electrodes, to the manufacturer's spec (commonly 0.030 inches, or 0.76mm, though this varies by model) using a gapping tool.

Fuel left sitting over the off-season degrades and can gum up the carburetor. Add a fuel stabilizer to a full tank before storage and run the engine briefly to circulate it through the fuel system, or drain the tank and carburetor completely if you'd rather store it dry. Either approach avoids starting problems in spring.

Riding mowers have a battery to think about too. A battery left unused and uncharged over winter can lose enough charge to fail. Connect it to a smart battery maintainer, a charger designed to hold a full charge without overcharging, for the storage period, or at minimum disconnect and store it somewhere that won't freeze.

Inspect and sharpen or replace the blade at the season boundary as well, since a blade that took a full season of wear benefits from attention before it either sits all winter or goes back into daily use.

If your riding mower is liquid-cooled rather than air-cooled (most smaller riding mowers use air cooling, but some larger models use liquid cooling similar to a car), check the coolant level in the overflow reservoir at season start and end, topping off with the manufacturer-specified coolant type.

Season start and end checklist

• Oil: change at season start or end, minimum annually or every 50 hours (push) or 100 hours (riding) per Briggs & Stratton, whichever comes first. Drain warm.
• Spark plug: replace annually or per OEM hour interval; gap to spec (commonly 0.030 in / 0.76mm, verify for your model).
• Fuel for storage: stabilizer in a full tank plus a short run to circulate, or drain tank and carburetor completely for dry storage.
• Battery (riding mowers): connect to a smart maintainer for the storage period, or disconnect and store somewhere that won't freeze.
• Blades: inspect and sharpen or replace at season boundary regardless of periodic sharpening during the season.
• Coolant (liquid-cooled riding mowers only): check level at overflow reservoir at season start and end, top off with OEM-specified coolant type.

Small engine maintenance guidance comes primarily from engine manufacturers and the industry association representing outdoor power equipment makers, since there's no single federal regulator covering lawn mower service the way there is for cars. These sources are worth checking for a spec specific to your engine.

• Briggs & Stratton: Maintenance schedules by engine model, oil type and capacity guidance, spark plug gap and interval specs, how-to guides for oil changes and filter service. briggsandstratton.com
• Outdoor Power Equipment Institute: Industry guidance on ethanol fuel blends, safe fuel storage, and general outdoor power equipment care. opei.org
• Your mower's engine and deck manuals: The authoritative source for your specific model's oil capacity, filter type, spark plug gap, and hour-based service intervals, which vary across engine families even within the same brand.

Small engine maintenance guidance comes primarily from engine manufacturers and the industry association representing outdoor power equipment makers, since there's no single federal regulator covering lawn mower service the way there is for cars. These sources are worth checking for a spec specific to your engine.

• Briggs & Stratton: Maintenance schedules by engine model, oil type and capacity guidance, spark plug gap and interval specs, how-to guides for oil changes and filter service. briggsandstratton.com
• Outdoor Power Equipment Institute: Industry guidance on ethanol fuel blends, safe fuel storage, and general outdoor power equipment care. opei.org
• Your mower's engine and deck manuals: The authoritative source for your specific model's oil capacity, filter type, spark plug gap, and hour-based service intervals, which vary across engine families even within the same brand.