Small-engine maker Briggs & Stratton has a reputation for building reliable, long-lasting equipment. The key to making the engine last is changing the oil once a year or after every 50 hours of use, as the company recommends in the instruction manual for the 4.5 engine found on many lawnmowers. Changing out the oil should take less than half an hour, using common household tools. Be sure to have the right replacement oil to refill the engine before using it again.
Run the engine for 2 minutes to warm the oil and make it easier to drain.
Disconnect the spark plug wire to prevent the engine from starting accidentally.
Remove the oil fill cap on the engine's side cover near the clutch, which is a spring-loaded lever. The oil fill cap will have a dipstick attached. Set the oil cap on a dry rag where it will not become coated with dirt or debris.
Examine the front of the engine block to locate a square drain plug. Remove the plug using a 3/8-inch open-ended wrench to twist counter-clockwise.
Tilt the engine on its side so that the spark plug faces upward.
Place a drain pan or old plastic milk container under the engine to catch the old oil.
Replace the oil filter if the engine is equipped with one, or clean a reusable filter. Some engines have a reusable filter that consists of a spongy substance inside a metal casing secured by a single screw.
Clean a reusable filter by squeezing out the old oil and soaking the sponge in warm soapy water.
Squeeze out the excess water and add a small amount of fresh oil to the sponge filter, no more than a tablespoon of oil.
Reinstall the cleaned filter.
Turn the engine right-side up and replace the drain plug.
Fill the engine with the amount of fresh oil recommended in the Briggs & Stratton owner's manual; typically about 14 ounces of SAE 30W Oil.
Replace the dipstick and oil cover.
Check the oil level.
Reconnect the spark plug wire to the spark plug.
