Is Your Lawn Mower Vibrating Badly? Possible Causes

Seriously excessive lawn mower vibration is a common issue that can be caused by several factors. I should know, I don’t only fix mowers with this problem, I’ve experienced it on my personal mower.

Long story short, I ran over a tree stump by accident. When the mower blade came into contact with the stump it produced a loud sound and the mower engine stalled immediately.

I disengaged the blades, raised the deck, and pushed the mower off the stump. I then started the mower and breathed a sigh of relief when it started right up again. But wait…

When I engaged the blade my lawnmower immediately began to shake really badly, almost violently. Surprised, I grabbed the wrong lever and lowered the deck when I meant to use the disengage lever, and my mower dug a circular hole in the ground before shutting off again.

You see, what happened is the mower blade bent when it came into contact with the tree stump and one side was pointing straight downward. Now unbalanced, that caused the entire mower to vibrate (and dig the shallow circle-shaped hole in my lawn).

While your shaking mower situation might not be as severe, it is likely caused by a similar issue.

Enough about my unfortunate lawn mower shaking adventure, let’s discuss all the possible causes your mower may be experiencing, too.

For help with other mower issues, check out our comprehensive guide on lawn mower repair.

What should I do if my lawn mower shakes exessively?

Shut it off, immediately!

Bad vibrations and exessive shaking are signs a lawn mower is no longer balanced and can cause engine damage or injury. Turn the mower off and investigate further to diagnose the cause of the skaking issue.

Possible Causes of Exessive Lawn Mower Vibrations

One of the main causes of lawn mower vibration is an unbalanced or loose cutting blade. This can happen the blade strikes a hard object like a rock or tree stump.

Another cause can be a damaged or worn-out drive belt, belt pulley, or pulley bearing. Inspect and maintain your lawn mower regularly to avoid these issues.

Why is My Lawn Mower Vibrating?

If your lawn mower is vibrating excessively, it is usually a sign of a problem that needs to be addressed promptly. In this section, we’ll explore some of the common reasons in a little more detail and explain what you can do to fix it.

Unbalanced Cutting Blades

One of the most common causes of lawn mower vibration is unbalanced blades.

Over time, the blades can become unbalanced due to wear and tear, hitting rocks or other debris, or improper sharpening. When the blades are unbalanced, they can cause the mower to vibrate excessively.

To fix this issue, you can either sharpen the blades or replace them with new blades if they are worn out.

If you’re not comfortable doing this yourself, you can take your mower to a professional for maintenance.

Worn-Out Mower Blades

Another reason why your lawn mower may be vibrating is worn-out blades. Over time, the blades become dull and worn, which can cause the mower to vibrate when in use.

To fix this issue, you should replace the blades with new ones. Make sure to choose the right size and type of blade for your mower. Good news, you probably won’t need to sharpen the new blades.

Damaged Mower Parts

Damaged parts can also cause your lawn mower to vibrate. Parts like the the engine mounting bolts, electric clutch, spindle housing bearings, and pulleys also require maintenance as they wear over time.

If any of these parts are loose or damaged, they can cause the mower to vibrate excessively.

To fix this issue, you should inspect the parts and tighten or replace them as needed. If you’re not comfortable doing this yourself, again, take your mower to a professional for maintenance.

Engine Problems

Finally, engine problems can also cause your lawn mower to vibrate. Some of the issues that can cause engine vibrations are as simple as a dirty air filter causing incomplete combustion

A clogged fuel line or worn-out spark plugs can contribute to mower vibrations, though they tend to happen gradually.

If the engine is not running smoothly but it’s been running rough for some time I recommend a complete tune-up.

To avoid engine issues, perform regular maintenance on your mower, including changing the air filter, cleaning the fuel lines, and replacing the spark plugs.

If the engine is still not running smoothly, you should definitely take your mower to a professional for an inspection.

Risk of engine damage

Exessive vibrations in a lawn mower come with a serious risk of causing engine damage, especially if the engine was worn or damaged already.

To diagnose the crankshaft and other internal parts, a complete teardown will be neccessary. If you have ruled out all of the “easy” things to check, your next stop will be to check the shear key.

When I ran over a tree stump the shear key should have done its job and broken to protect the rest of the engine, but it didn’t. Thankfully there was no further damage, but the shear key was visibly dented and I replaced it out of precaution.

Summary

I don’t recommend you perform any task you’re not comfortable with, or sure you can do it right. Check the blade first, and the belts, pulleys and mounting bolts. Anything beyond that requires a bit of mechanical aptitude and some small engine repair tools.

Performing regular maintenance on your mower, avoiding running over hard objects, and addressing any issues promptly, will help keep your mower running smoothly and prevent excessive vibration.

Note: I’ve included tips for troubleshooting riding mowers in this guide but most of the tips apply to push mowers as well. Happy mowing!