Why Is My Lawn Mower Vibrating? Find Out Here

Written By James
Updated May 8, 2022 by James

Why Is My Lawn Mower Vibrating? Find Out Here

Although on the surface this question may seem slightly redundant, excessive vibrations can be a cause for alarm in your lawn mower. The gentle hum and din of a healthy engine, or the very distressing bad vibration of a damaged motor, are two seperate sounds and feelings you can quickly catch on to.

Why is my lawn mower vibrating? Extreme lawn mower vibrations can be a result of damage, blockage, or typical wear and tear of various parts. Mower blades, the engine, crankshaft, flywheel key, and even the pullies could be a possible source of vibration.

Identifying the exact issue can be tricky, and you're probably going to need to take a look under your mower deck. Luckily for you, this guide will help you spot any naging issues your mower might be facing, no matter where the source of the issue is. So keep reading to spot your lawn tending problems. 

Mower Blades

More often than not, the mower blade is the source of severe vibration. Damaged or out of balance blades can cause excessive vibrations, but most mower blades are large in size and therefore easy to find a fault with. Loose blades will need to be tightented if you want to prevent an out of balance blade, and testing for balance is an easy task. 

While there are different tools and devices available for testing mower blade balance, simply hanging your blades on a nail via the center hole will show you everything you need to see. If you find no lawnmower blade faults with this method, then don't go putting the mower blade back in just yet.

A loose cutting blade isn't the only way for the blade cutters to cause a harsh vibration. Improper sharpening can lead to a duller spinning blade, which will then cause mower vibration. If this is the source of your lawnmower vibration issues, then consider sharpening or replacing a potentially damaged blade.

A damaged cutting blade can't always be fixed or repaired, so if the blades continue to cause issue then you may need to shop for a replacment. If the unbalanced cutting blade isn't the vibrating culprit beneath your mower deck, examine your blade belt. 

The blade belt is exactly what you might imagine it is. It is the driving force between the mower blade and the engine. Worn down belts will cause results similar to an unbalanced blade, leading to uneven cuts and bad vibration. 

Ater testing your blade for balance, inspect your blade adapter pins. These are the fittings that make sure your lawnmower blade remains attached to the rest of the equipment. If faulty, the blade adapter pins can undo any of the tightening you may do to loose blade, rendering your repair work useless. 

Mower Engine

Potential engine wear may seem like the more obvious cause of lawnmower vibration issues, as the engine uses constant combustion to drive the mower. While the very traditional push mowers with reels lack an engine, modern gas powered and electric models still use an engine of some degree. 

While an entire engine may be difficult to insect, certainly without proper training and knowledge, your average mechanic's car and engine shop may be able to help. Failing this, look online for your engine manufacturer who may have design specifications published so you know what a healthy engine looks like.

If you discover you are using a flathead engine lawn mower, then you're in for a tough time. These engines require professional help, and are infamously difficult to repair at home if you end up with a fault. Adjusting certain components of these engines can be rather difficult, while other sections are beyond the scope of the average gardener.


If you're looking for more precise sources of an issue in an engine, then your first port of call should be the crankshaft. Acting as the go between for the pistons and the flywheel of an engine, crankshafts are exerted under constant stress when an engine is running. Most commonly, this results in the crankshaft bending. 

While even severe damage can be generally handled when it comes to the crankshaft, without proper tools to fix the shape they can become unfixable. This irreparable damage of course means you will need to purchase a replacement for it, but at least you don't have to throw out the entire engine.

Rotating at high speeds, a worst case scenario would be the crankshaft actually coming loose. This would be a rare and terrible occurence, as it would also lead to a loosening of the mower's blades to some degree. As previously discussed, this can easily make your mower vibration problems far worse, and cause damage to more parts of the equipment.

Bending in the crankshaft, often caused by hitting an object that the mower can't move past, will often coincide with blade damage. This is because large rocks or tree stumps easily mess up the motion of the cutting blades, which can reach incredibly high speeds. Much like a car crash, suddenly coming to a halt can cause serious damage. 

Since the blades are moving so fast, suddenly stopping means that the energy being expended to move the blades has to be suddenly transferred somewhere else. This is usually to components inside the mower. 

Flywheel Key

What is a flywheel key? Essentially, the flywheel key is a protective failsafe. Placed between the flywheel and crankshaft, the flywheel key is designed to absorb damage from suddent stoppages. This mostly involves the mower hitting a solid object, such as a tree root or a tree stump. Some stones can be large enough to stop the mower as well.

Essentially, the flywheel is a shock absorber and a method of cooling the crankwheel, which can reach speeds similar to the blades. The key also keeps the flywheel and crankshaft aligned, meaning that it's absence can quickly lead to the two pieces separating. 

This will cause your mower to start performing poorly, and start the vibrations. Many other parts connected to these two core components will also fail to function correctly in the way that they were designed to, and it should be your first sign to start some proper repairs.

The flywheel key typically breaks on hitting a solid object, and in doing so the mower will jolt to an absolute halt. Your vibration problems could indicate that you are missing a flywheel key, and you will need to replace it before you use your lawn mower again. 

By stopping so suddenly, the key protects damage to more expensive and difficult equipment. Without it, a tree root could easily get caught up in your blades, or engine, and cause enough damage that it might be cheaper to buy a new mower than to repair your existing one. 

The flywheel itself can be easily inspected for damage, and replaced at your own discretion. Both the flywheel and flywheel key can cause excess vibration, so make sure any damage is detected quickly. As already stated, a poor flywheel key can lead to significant damage to more expensive parts of your mower.


Attaching your lawn mower deck to the blade, a mandrel can wear down with consistent and regular use. In addition, unbalanced blades put extra stress on the mandrel, and can lead to a more rapid decline. Hitting a solid object such as a rock will also throw off the mandrel's bearings.

Along with vibrations, if you happen to notice an uneven cutting from your mower and buzzing (or on occassion some squaling) noises, then worn bearings in the mandrel may be your culprit. Thankfully, these are easier to repair and replace, and require less expert knowledge than an engine or blade repair.

Available in most hardware stores, only basic tools are needed to replace the bearing on a madrel assembly. In fact, you'll be more likely to spend more time reading how to do the task than actually performing it. Mandrel wear is perhaps one of the more explicit vibrating problems, thanks to the other signs that accompany it.


If you find none of these problems to be the source of the harsh vibrating, then you should check your pullies. A pully is a part of your lawn mower's transmission, and problems surrounding it typically arise from blockages and obstructions. 

As you mow, grass can easily start to clog the pully. Not to mention other things such as dead bugs, small twigs, leaves, and more. This should be your final inspection if nothing else in this article solves your vibration issues.

Common Causes and Fixes

If you don't have any experience repairing lawn equipment, feel uncomfortable doing it, or feel concerned over the safety of handling blades and engines, then please visit a specialist store. Lawn equipment repairs shops or potentially a local hardware store may be able to help with your issue and can help service your mower.

Issues with vibration, unlike most mowing challenges, don't always arise from maintenance. Or rather, a lack there of. Other than routinely cleaning your pullies to prevent blockages, most of these damages you'll be finding in this article are natural results of mower use, and standard wear and tear. 

Instead, it is how you use your mower that will cause the majority of these problems. Large stones and tree debris can cause sudden jolts, stoppages, and even broken interior equipment such as the flywheel key. It is important that the protective measures put in place by lawn mower manufacturers are kept in place, otherwise your repair bill may go up more than you expect.

Other than full replacement and the odd clean, there is no quick fix for a harshly vibrating lawn tractor or push mower. When servicing your mower, be sure to disconnect the spark plug to ensure proper safety, as lawn mower blades can reach speeds of more than one hundred miles per hour. 

Although sharp, most damage to the equipment should be visible. Bends where they shouldn't be, notches in the blades, either missing or present. As a result, with the exception of flathead engines, the majority of fixes for your vibrations should be doable at home.

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My father, and his father before him, and his father; for the past 3 generations, my family have always been into gardening. The green fingers is a gift passed down to me and I thoroughly enjoy it! I also have worked in the manufacturing department for Bosch and DeWalt so I like to think I know a thing or two about tools and such!
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