Outdoor Power Equipment, Small Engine, Lawn Mower Repairs, Troubleshooting and Safety

There are number of simple but crucial requirements to help ensure the long life and reliability of your machine powered by a small gas engine. Not surprisingly, first on the list is clean oil of the correct type and quantity, and changed at suitable intervals.

Oil performs four functions. The first is, of course, lubrication. By providing a thin, slippery layer between moving internal engine parts, oil reduces friction, generation of heat, and wear. Second, as the oil flows over hot spots it carries heat away to cooler areas such as the sump and crankcase walls where outside air picks up the heat and dissipates it to the environment. In larger liquid-cooled engines this function is shared by the coolant and oil, but smaller, hotter-running air-cooled engines rely on heat dissipation by oil and by air. Fins cast into the block, especially around the cylinder, allow air circulated by the flywheel fan to carry away much heat. Third, oil keeps internal parts clean by collecting and suspending particles of metal, dust and carbon that break away from engine components or find their way from the outside. Detergent oil contains additives specifically for this purpose. Oil used in small gas ( air cooled ) engines should ordinarily contain no other additives. Fourth, oil provides a seal between the cylinder wall and the piston rings, where otherwise a larger amount of combustion products would blow by.

Changing the Oil

If the engine is in running condition, run it for a few minutes until it is at operating temperature. This will heat up the oil and stir up whatever sludge or sediment may sitting on the bottom of the sump, suspending it in the oil. Warm oil flows much more easily and will carry contaminants with it. It will drain more quickly and more completely.

Many engines used on walk-behind lawn mowers have a drain plug on the bottom, accessible from the mower blade area. If not, you can tip the mower on its side, carburetor side up, to drain the oil out the fill tube or fill hole. A block of wood or other device may be helpful to support the mower at a convenient angle.

If your engine has a dipstick, check the manual to see if the dipstick should be threaded into its fill tube when checking oil level. Kawasaki engines used on commercial walk-behind mowers specify not to turn the dipstick cap onto the fill tube threads for correct oil level (see Photo 3). Photo 8 shows pictorially not to screw the dipstick onto the fill-tube on this Kawasaki FB460V engine. The label also gives the viscosity and oil change intervals. The Honda label in Photo 6 shows the correct oil level. Engines that do not have dipsticks usually should be filled to the top of the fill hole.

Most other engine applications don't permit tipping the machine over to drain oil. There will be a drain plug somewhere at the base of the engine. Photo 5 shows a typical oil drain plug. This plug can be removed most easily with a 7 / 16" eight-point socket. If you're lucky, the manufacturer will have provided a drain cock or pipe that allows oil to drain easily into a catch basin. If there is no means by which to drain oil conveniently you would do well to install one yourself. Perhaps, the most convenient type is the one shown in Photo1. You unsnap the yellow cap, attach a tube to lead to a catch basin, give the drain a twist to the left and pull slightly forward. No tools, no mess.

It is important to select the correct oil viscosity grade for your engine. Higher viscosities are needed in hotter situations to maintain necessary lubrication but in cold situations the oil should be thinner so that it flows more readily. An engine can be significantly easier to start in cold weather when a lower viscosity oil is uesd. The manufacturer will state in the owner's manual what viscosities are acceptable and what volume is required. The viscosity required will generally depend on the ambient temperature in which the machine will be used. Warmer weather - above 40°F - calls for thicker oil, typically SAE 30W (SAE = Society of Automotive Engineers). Cooler weather calls for 10W30, and cold weather calls for 5W30 (as used in snowthrowers). These are only general guides. Check your owner's manual for the manufacturer's recommendation, e.g. SAE 30 should not be used in Kohler Command engines ( see Photo2 ).

Check the owner's manual for the manufacturer's requirements for oil viscosity in the temperature range in which the machine will be used, and for the proper way to check the oil level. If you do not have the owner's manual, most are available on-line at the engine manufacturer's website. Engine manufacturer's websites are listed in the Parts Lookup Directory section of this site.

Disposal of Used Motor Oil

The EPA estimates that 40% of oil pollution comes from do-it-yourself oil changes - that's you and me disposing of used oil improperly. DIYers use more than 200 million gallons of oil per year. More than half of that is wasted. Where does it go? One quart of oil can pollute 250,000 gallons of water.

Recycle your used oil. Many communities have recycling centers where oil, paint, batteries and other potentially harmful materials can be disposed of. Many major retailers that sell oil or perform auto service will accept waste oil at no charge. 95% per cent of AutoZone stores accept used oil and other fluids and 100% of them accept old lead-acid batteries. Advance Auto Parts accepts batteries and oil. Other shops burn used oil for heat and will gladly take your used motor oil. If you don't know where to dispose of your old oil, make a few phone calls, ask your neighbors. Give a hoot. Don't pollute.