Why Is My Lawn Mower Vibrating Bad? [6 Main Reasons]

Have you recently been mowing the lawn and felt that something isn’t quite right with your lawn mower?

Pay attention, your lawn mower may be vibrating. 

If your lawn mower is vibrating badly, then you should find out the problem and rectify it immediately.

Not to worry, most of the lawn mower repair works are easy!

Whether you’re a novice or a lawn-mowing pro, anybody can repair a vibrating lawn mower.

We’re here to break down what causes your lawn mower to vibrate and provide handy tips and tricks to prevent it. 

Most lawn mowers start to vibrate because a certain part of the machine is damaged or poorly installed.

Some of the parts that make the lawn mower vibrate are the cutting blade, valves, spark plug, flywheel, crankshaft, and blade adapter pins.

In this guide, we will highlight some of the things that cause the lawn mower to vibrate badly.

Lawn mowers are vital machines that help us to trim grass quickly and efficiently.

So, if your lawn mower is vibrating critically, it may slow you down.

Here are some of the leading causes of gas lawn mowers vibrating severely and how to rectify the issue.

1. Unbalanced Blade

The leading cause of lawn mower vibration is a loose or unbalanced cutting blade.

Many things can make the blade loose or unbalanced.

When you hit a rock, tree root, or metal as you trim grass, you may cause the blade to loosen or chip a small part.

If the blade is chipped, then it will be unbalanced.

Improper sharpening is another reason that may cause your blade to be unbalanced.

If you sharpen one side of the blade more than the other, it may be heavier, thus creating imbalance.

How To Fix It

If an unbalanced blade is causing your lawn mower to vibrate severely, you can balance it using a blade balancing tool.

Alternatively, you can sharpen the blade to make both sides balanced.

And if you have got a loose blade on your tool, simply tighten it to make the vibrating stop.

2. Damaged Cutting Blade

If you use the lawn mower regularly, then you know how easy it is to damage or dent the cutting blade.

This is common in areas with a lot of trees or stones.

That’s why it is advisable to check the area where you want to cut grass.

If the blade hits a metal, tree root, or rock, there is a high chance that it will be damaged.

Instead of proceeding with cutting grass, you should inspect the blade and see if it’s damaged or not.

This can result in severe vibration.

How To Fix It

Replace the damaged cutting blade right away. A damaged blade can cause more havoc by affecting other parts of the lawn mower.

3. Damaged Flywheel Key

When the cutting blade hits a rock or tree root, the damage goes far beyond the cutting blade.

Other parts such as the flywheel key, are damaged too.

For this reason, you need to inspect it before coming to a conclusion.

The flywheel works simultaneously as a shock absorber and a cooling fan.

So, if it’s damaged, your machine won’t work well and will start vibrating.

On the other hand, the flywheel key keeps the flywheel and crankshaft aligned.

If it’s broken because of the force, many parts won’t function properly.

How To Fix It

Replace the damaged or broken flywheel key with a new one.

Leaving the damaged flywheel key on the lawn mower will only cause more harm than good.

We recommend purchasing OEM parts for the smooth operation of your lawn mower.

4. The Engine Requires Tuning Up

Not all lawn mower vibrations occur as a result of the blade hitting an obstacle in your yard during trimming.

Some vibrate because the engine runs rough or won’t start.

If the engine is not tuned up, it will continue vibrating excessively.

How To Fix It

Simply tune up your engine.

Tuning up your lawn mower’s engine often will help to increase the engine’s efficiency.

Apart from that, it will prevent engine wear and tear.

5. Damaged Crankshaft

The crankshaft is one of the main parts of your lawn mower’s engine.

Since the blade attaches directly to the crankshaft, damage to the blade has an impact on the crankshaft.

If a blade hits a rock or metal, all the energy is transferred to the crankshaft.

This may cause slight or severe damage, depending on the force transferred.

How To Fix It

Start by checking the blade.

If it is damaged, then the crankshaft is damaged.

However, before you repair the crankshaft, you should repair or replace the blade.

Ensure that all the other parts are fine, such as spark plugs, blade adapter pins, and valves, before fixing the crankshaft.

Unlike other lawn mower parts, repairing the crankshaft is time-consuming and cumbersome.

It is also costly and should not be done by newbies.

Get a professional to repair the part or just buy a new engine altogether.

6. Valves Need Adjusting

If the blade and engine are okay, but your lawn mower is still vibrating badly, then you need to check the valves.

Most lawn mowers come with overhead valves, which are easy to adjust.

But if you own a flathead engine lawn mower, then adjusting the valves will be quite challenging.

Failure to adjust the valves causes trouble when attempting to start your lawn mower.

It can also lead to vibration, which is very irritating.

How To Fix It

All you need to do is adjust the valves to their ideal position, and the machine will function perfectly.

Lawn mowers with OHV engines are simple to adjust, while those with flathead engines require professional help.

Final Thoughts

A lawn mower needs proper care and maintenance to last longer.

It doesn’t matter if it’s a gas, electric, or battery-powered lawn mower, you should ensure it is always in top form.

Always use the right type of oil for your machine to run smoothly.

In addition, don’t attend to your yard aimlessly without looking out for rocks, tree roots, or even pipes.

If there is a damaged part that needs replacement, be sure to use a new, correct replacement part.

Unbalanced, damaged, or loose cutting blades are the primary cause of extreme lawn mower vibrations.

However, the other reasons covered above can also lead to your lawn mower vibrating.

Our advice – take good care of your lawn mower and avoid cutting obstacles that may endanger it.

We wish you all the best as you embark on repairing your gas-powered lawn mower!