How to Use a Lawn Mower: Sticks and Stones May Break Your Blade!

As you've learned from previous posts about the significance of preventive maintenance to extend the life of your lawn mower, you might wonder how to use your mower effectively to ensure its longevity. This guide will detail methods to help your lawn mower last for years by avoiding a common problem: hitting blade obstructions!

Before using your lawn mower, make it a habit to inspect the grass area you plan to mow, watching for anything that could collide with a blade spinning at speeds up to 1900 RPM! Objects like rocks, small stones, twigs, branches, yard ornaments, and edging can cause damage. Hitting an object with a spinning blade could bend or damage the cutting blade or, worse, result in an irreparable engine (at least not one economically feasible to repair).

Manufacturers recognize the risk of hitting hard objects while mowing, so they designed a component called a flywheel key. The primary purpose of this key is to effectively "time" the crankshaft with the flywheel. This timing is essential for the proper running of the engine. If the blade hits a hard object, the impact is absorbed by the spinning flywheel and its key (made of a softer metal material), which spins in sync with the blade. The key "shears" upon impact, effectively shutting off the engine before the impact reaches and is absorbed by a critical engine component, the crankshaft. This is not a foolproof or even reliable measure to prevent engine damage, as hitting a hard object might still leave the mower unable to start and with a bent crankshaft, depending on the severity of the impact.

What to do if you suspect you've hit a hard object and your lawn mower won't start:

First, disconnect the spark plug wire from a non-running engine to prevent accidental startup. Next, flip over the mower (keeping the carburetor facing up!) to prevent oil and gas from spilling into the carburetor or air filter. Refer to this post on how to tilt your mower safely How to Properly Tilt Your Lawn Mower On Its Side: Your Probably Doing It Wrong! Then, inspect the blade for any obvious damage such as nicks or cracks. Also, spin the blade with a gloved hand to check if the blade or crankshaft (the shaft the blade is attached to) is bent. Pay close attention to the space between the blade's outer edge and the deck's edge nearest the blade. If the space is consistent all around, the crank is likely not bent. If not, the crank and/or blade is bent, requiring further repair. In this case, the shear key may have completely broken into two pieces, preventing the engine from starting.

Using a gloved hand spin the blade by hand and ensure the gap is consistent all the way around the edge of the deck, if the gap varies the blade and or crank is likely bent

Another scenario involves a partially sheared key. In this situation, the shear key has not completely broken into two pieces, but is partially deformed. Here, the lawn mower sustained an impact but may still start and run, albeit out of "time". Check if it's vibrating excessively. This happens because the blade helps balance the engine, and if the blade or crankshaft is bent, it disrupts this balance, causing vibration.

Another clear sign of a partially

sheared key is when the pull rope is violently pulled out of your hand after starting the mower, potentially harming you, the operator. In order to properly diagnose the flywheel key, the flywheel must be removed and a new key would have to be installed if no other damage occurred.

The good news is that all these unfortunate situations can be avoided by taking the time to inspect the mowing area and remove potential blade obstructions before you hit them!

Refer to this summary card on what to do if you happen to hit an obstruction

If you found this post helpful consider enrolling in our free Online Program designed to transform novice lawn mower operators into knowledgeable and independent troubleshooters, and maintainers of their own equipment! Avoid the expense and hassle of untimely breakdowns! All that is required to enroll is an email, and it is completely free of charge! Click here to be directed to the enrollment page: Online Program

Never the Norm!