Year round care of rotary mowers with four stroke gasoline engines

Before the mowing season, buy a new spark plug. Following the engine maker’s specifications, set the gap between the two metal electrodes at the plug’s threaded end. Use a spark-plug gauge’s bending bracket on the Lshaped side electrode to adjust the gap. Take out the old spark plug, connect the wire to the new one, and rest the plug’s threaded surface on the engine.

Crank the engine; if there is steady sparking between the two electrodes, install the spark plug. If there’s no spark or if the spark is erratic, remove the sheet-metal cover over the fly wheel, and inspect the magneto coil and the entire length of the plug wire. If either is damaged, replace it; on many mowers it is one component. If you see no damage, have a professional check the electronic ignition.

If you have an older lawn mower with ignition points instead of electronic ignition, you should inspect the points and adjust the gap between the contacts. However, the points are under the flywheel, and to remove the flywheel, you need special tools. You can avoid buying special tools by installing an electronic ignition conversion kit, which is less costly than the tools. Once the kit is in, the points need never again be serviced.

Check that the spark plug wire terminal fits tightly on the plug. If it is loose, push back the rubber nipple and crimp the terminal with pliers.

If the starter is a pull-rope type, inspect the rope for fraying and replace it if necessary.

Remove the air-filter cover and inspect the filter element. Replace the pleated paper type if it’s dirty. Clean a plastic-foam filter by immersing it in kerosene, then gently squeezing the kerosene through it; allow it to airdry. Soak it in clean engine oil, gently squeeze out the oil, and reinstall.

Spray the carburetor linkage with penetrating oil. Also spray penetrating oil on the axles.

If the mower has chain or belt drive, check the chain or belt for looseness. Press on it with a finger. If a belt deflects more than 3/4 inch between pulleys, or if a chain deflects more than 1/8 inch between sprockets, readjust it. In most cases, loosen engine-to-mower bolts, which pass through elongated holes, and move the engine forward or back as necessary. For other, less common belt arrangements, see Drive belts. Belts that are automatically tensioned by a spring-loaded pulley cannot be adjusted; replace the loose belt. Tighten the engine-tomower bolts.

Inspect the blade, and if it is badly nicked, replace it or have a professional sharpen it. Don’t try to file away anything other than minor nicks, or you’ll unbalance the blade, putting an uneven load on the engine and causing damage.

If gasoline was left in the tank during the winter, gum may have formed, making the mower difficult to start. To clean out the gum, pour a pint can of carburetor solvent into the tank; fill with gasoline. Prime the engine: remove the air filter and pour 2 to 3 tablespoons of clean gasoline into the bottom of the filter housing. Midseason checkup Inspect the air filter and if it’s dirty, clean or replace it. Do a major cleaning ofthe mower body. Change the engine oil while the engine is hot. Tighten the engine-to-mower mounting bolts. Check the blade for nicks.

End of season

Drain the gas tank and run the mower out of gas. Immediately change the oil while the engine is still hot. Let the engine cool, remove the spark plug, and pour 5 tablespoons of fresh engine oil into the spark-plug hole. Crank the engine for 3 seconds to circulate the oil; then reinstall the spark plug, but don’t reconnect the plug wire. To retard rust, spray penetrating oil on all exposed shafts, linkage, sprockets or gears, chains, and axles.