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How to Break in a New Lawn Mower Engine

A new lawn mower is a valuable tool which, if cared for properly, can last you for many lawn-care seasons. One of the first steps in caring for your mower is to properly break in its engine. New mowers need to have the piston rings, the cylinder walls and the connecting rods all properly impregnated with oil in order for the engine to run smoothly. Once broken in, most engines will operate for many years with simple standard maintenance.

Fill the engine with either a 2-stroke or a 4-stroke engine oil, depending on the type of engine your mower has, if it is not already filled. Do not overfill it. Check the fullness of the engine by removing the oil dipstick and visually inspect the height to which the oil has reached. Follow the manufacturer's directions for filling the engine.

Start the engine and allow it to idle for five minutes.

Increase the throttle to 1/2 after the engine has idled for five minutes. Run the engine at 1/2 throttle for five minutes.

Return the engine to idle and allow it to run for three to five minutes. Then shut the engine off.

Allow the engine to cool for 30 minutes. Use your wrench to remove the oil drain bolt on the bottom of the engine and drain the oil into an oil drain pan. It may be necessary to put the mower onto blocks in order to raise it up to facilitate access to the oil drain plug. Be careful when draining the oil as it will still be hot.

Replace the oil drain plug once the oil has drained from the engine. Tighten the plug snugly with your wrench, but do not overtighten it

Refill the engine with fresh oil designed for either a 2-stroke or a 4-stroke engine (depending on which type you have). Check your oil dipstick to make sure you have added enough oil. Do not overfill. Your engine is now broken in and ready for normal use.


Wear gloves when removing the oil drain plug as hot oil could spill onto your hand. You may use special small engine break-in oil to break in your engine, but this is not necessary. Any good natural or synthetic oil designed for your engine type (2-stroke or 4-stroke) may be used.

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