As a small engine repair pro, you know the drill: your clients rely on their lawn mowers—whether push, zero-turn, or tractor—to keep their yards pristine. A well-maintained mower doesn’t just cut better; it lasts longer and breaks down less.
While the owner’s manual has the basics, we’re going beyond. A 100-hour service is more than an oil change; it’s a deep-dive that prevents costly breakdowns during the peak season.
Here is the definitive, pro-level checklist for your clients or your own shop, designed to keep those engines humming past the 100-hour mark.
1. Engine Systems Check (The Heart)
This is the core of any small engine service. Don’t just check; inspect for signs of wear and tear.
- Change the Oil and Filter: Use the manufacturer’s specified oil weight. Always pre-fill the new oil filter with fresh oil to prevent a momentary “dry start.”
- Replace the Spark Plug: A fouled plug causes misfires, fuel waste, and hard starting. Replace with a new plug gapped to spec. Pro Tip: Inspect the old plug’s tip for clues about the engine’s running condition (black, sooty deposits indicate a rich mixture).
- Replace the Air Filter: A clogged filter chokes the engine and causes it to run rich and hot. Use a new filter. For paper filters, never try to clean them; for foam filters, wash and re-oil per the manual.
- Fuel System Inspection:
- Change the fuel filter.
- Inspect all fuel lines for cracks, brittleness, or leaks. A small leak is a fire hazard.
- Check the carburetor bowl (if applicable) for water or sediment. Drain and flush if needed.
- Inspect the fuel cap vent to ensure it’s not blocked.
2. Electrical and Charging System (The Spark)
The battery and charging system are often ignored until the mower won’t start.
- Test the Battery: Use a load tester to check its cranking capacity, not just its voltage. Clean any corrosion from the terminals and apply dielectric grease.
- Check the Alternator/Stator Output: Ensure the charging system is providing the correct voltage (usually between $13.5$ and $14.5$ volts) when the engine is running at $3/4$ throttle.
- Inspect Wiring Harnesses: Look for frayed wires, loose connections, or spots where insulation has been rubbed through by vibration, especially near the frame or sharp edges.
3. Cutting Deck and Blade System (The Business End)
This is where the power meets the grass. Neglecting the deck can lead to poor cut quality and excessive strain on the engine.
- Remove, Sharpen, and Balance Blades: Sharpening is essential, but balancing prevents vibration that can destroy spindles and accelerate bearing wear.
- Grease and Inspect Spindles: Apply grease (if equipped) to the spindle bearings. While spinning the blades by hand, listen and feel for rough or wobbly bearings—replace them immediately if you find any play.
- Clean the Underside of the Deck: Thoroughly scrape or wash off caked-on grass clippings. This prevents rust and ensures the grass discharges correctly.
- Check Belts and Pulleys:
- Inspect the deck belt and drive belt for cracking, fraying, or glazing. Replace if they show significant wear.
- Ensure all idler and tensioner pulleys spin freely and quietly.
4. Drive and Control System (The Mobility)
Whether it’s a hydrostatic transmission or a gear drive, these components need attention.
- Hydrostatic Transmission (if applicable):
- Check the hydraulic oil level and condition. Most manufacturers recommend a filter change at the $100$-hour mark, so consult the manual and follow the exact procedure for bleeding the air out of the system.
- Clean the cooling fins on the transmission.
- Wheels and Tires:
- Check tire pressure—uneven pressure leads to an uneven cut.
- Inspect the tire tread for wear.
- Grease the front axle pivot points and wheel bearings (if applicable).
- Control Linkages and Cables: Lubricate all throttle, choke, and deck lift cables with a quality cable lube. Ensure the brake and clutch linkages operate smoothly and engage fully.
The Final, Critical Step: Test Run and Safety
The job isn’t done until the mower passes a real-world test.
- Test Run: Start the engine and let it warm up. Listen for any new noises. Test the throttle response at full speed and idle.
- Check Safety Switches: This is non-negotiable. Test the seat switch, PTO switch, and safety bypass switches. The engine must cut off when the operator leaves the seat with the blades engaged.
- Final Inspection: Torque all wheel bolts, blade bolts, and any other fasteners that were removed or checked.
By following this definitive checklist, you’re not just performing a service; you’re delivering peace of mind and significantly extending the life of a valuable piece of equipment. Time to go get those hours!