Change the oil.This is the most important thing you can do to make your engine live forever. Change your oil with a good grade of SAE 30w HD For Service SC and higher. On Tecumseh Snow-King engines, use only 10w-30 HD For Service SC and Higher. Change your oil every 50 hours or once a season, which ever comes first. Do not overfill! This will cause the engine to smoke or blow oil out of the breather into the air filter. On engines with dipsticks, fill to the top line of the crosshatch mark. On engines without dipsticks, fill to the top of the hole. On horizontal engines without dipsticks, fill until oil comes out of the fill hole.
Clean or replace the air filter.This is also a very important part of engine maintenance. Clean the foam filters with hot soap and water. Re-oil and squeeze out excess. Paper elements must be replaced if extremely dirty of have dirt caked up in the pleats. Pre-cleaners must be washed like foam elements. Do not oil pre-cleaners that say DO NOT OIL. Air filters must be cleaned/replaced every 25 hours or more often under dusty conditions.
Change spark plugs.As cheap as some spark plugs are (in cost) it’s a good idea to just replace them once a season instead of trying to clean them and reuse them. This is sometimes the culprit on engines that are hard to start or engines that will not start at all.
Sharpen and balance blades.A dull blade will put more load on an engine than a sharp blade will because the engine has to re cut the grass more. Also your yard does not look too good when the grass gets pushed down, not cut. An out of balance blade obviously makes things vibrate bad, puts extra load on the engine, and wears things out prematurely.
Remove debris from fins.Your car won’t exactly cool down running it without water, right? So what makes you think a small engine can cool if its fins are packed full of grass, leaves, etc.? Remove the shroud yearly or more often under dirty conditions to remove leaves and dirt from the flywheel, cylinder fins, head fins, under the flywheel, and behind the muffler. Be sure to remove the piece of shroud from under the cylinder. Lots of stuff gets stuck in there also.
Remove or stabilize fuel before storing engine.Doing this will prevent unwanted maintenance in the spring time. When gas is untreated, it will start to turn into a gel after 60 to 90 days. When the fuel turns into a gel, it clogs up the jet in the carburetor, making it impossible to start the engine.
To remove the fuel from the tank (push mowers) place a pan suitable or containing gas and place it under the fuel line where it connects to the tank. Remove the spring clamp and pull off the hose. Let fuel run out completely into pan and dispose of properly. Start engine and run it until it dies on its own.