Power Lawnmower Maintenance

Richard L. Parish, PhD, PE

A power lawnmower requires regular maintenance if it is to continue to provide reliable service. Most of the maintenance steps are easy and can be done by a reasonably handy homeowner. All of these steps should be done at the end of the season prior to storage, and some should be done more often. Consult your operator’s manual for specific recommendations

Blade Sharpening: Mower blades are easy to sharpen. Before removing the blade, remove the spark plug wire so there is no danger of accidentally starting the engine while turning the blade. If you are going to change the oil at the same time, it is helpful to go ahead and drain the oil before turning the mower on its side. If you leave the oil in the mower, check your operator’s manual to see which way it is better to turn the mower to prevent oil leakage. Most blades can be removed by loosening one bolt on the drive shaft. You should either block the blade with a chunk of wood or use a wad of rags (or heavy gloves) to hold the blade and keep it from turning. Don’t hold the blade bare-handed; you might be cut by the blade. Once the blade is removed, it must either be sharpened or replaced. Most blades can be sharpened several times before replacement is needed. If the corners of the blade are rounded off or the ends of the blade are thin, the blade should be replaced. You can sharpen the blade with a bench grinder or a small angle-head grinder (hold the blade in a vise while sharpening), use a file (again with the blade in a vise), or take it to be professionally sharpened. After sharpening, the balance of the blade must be checked. This can be done by holding the blade on a round rod through the hole and seeing if it balances. If not, the heavy side will require more grinding or filing. Replace the blade and tighten the bolt. If the operator’s manual gives a torque spec, use a torque wrench.

Cleaning: One of the best things you can do for your mower is to keep it clean. Grass clippings are very corrosive; if you allow them to build up under the deck they can corrode your deck rapidly. You should keep both the top and the underside of your mower deck clean. If the clippings are not wet and stuck to the deck, a leaf blower or air compressor will clean the deck very effectively; if the clippings are wet or stuck, you will need a water hose. It is also important to keep the engine clean. Lawnmower engines are air-cooled and the cooling fins must be kept clean to be effective and prevent overheating.

Oil Change: You should change the engine oil using the frequency recommended by the operator’s manual. For typical home lawn use, once a year is probably adequate. If it takes more than an hour to mow your lawn or if you operate in very dusty conditions, you might need to change oil twice a year or more. Just drain out the old oil into a suitable container for recycling and add new oil of the correct viscosity and API rating. Some engines can be drained from the bottom; on others, it is necessary to turn the mower on its side to drain the oil. It is helpful to drain the oil while the engine is warm; this makes the oil flow better and also gets any dirt particles into suspension so they will come out with the oil. Add the recommended amount of oil and then check the level. Be careful to not get dirt into the crankcase while adding oil.

Other Lubrication: Some mower operator’s manuals will recommend oiling axles or other components. Some mowers also have grease fittings that should be serviced with a grease gun as recommended in the manual.

Air Filter: The air filter must be cleaned or replaced regularly. The more dusty your conditions, the more frequently the air filter will need service.

Spark Plug: Remove the spark plug and examine it for signs of problems. Although spark plugs can be cleaned and reused, it is better on a small engine to just install a new one. Set the gap to the specifications in the operator’s manual using a plug gap gage and install the plug using a torque wrench. Use the torque specified in the manual.

Following these simple steps can go a long ways toward making your mower easy to start and keep it running well for many years.