At some point in the lifetime of your lawn mower, you may notice that it is vibrating more than normal and sense that something isn’t quite right. If you’re not careful and you don’t take action, this could develop into your lawn mower shaking violently and quickly becoming a major problem. In this article, I’ll dive into what could be causing the vibration and how you can diagnose the symptoms to avoid a costly repair.
Why is My Lawn Mower Vibrating Really Bad? (The Short Answer)
Moving parts that have uneven weight distribution can cause lawnmower vibration problems. Unbalanced blades or loose blades are moving parts that, if damaged or incorrectly installed, will cause a lawnmower to shake and vibrate.
Common Causes of a Lawn Mower That is Shaking Bad
In my experience, the exposed parts of the lawn mower are the first areas where vibrating starts. As time goes on, these issues can progressively get worse. So let’s check out the common causes that will make your lawn mower shake.
Unbalanced Blades
An unbalanced blade is a result of one side of a blade being heavier than the other. This can occur by wear from cutting the lawn and poor sharpening. The heavier side of the blade unevenly distributes the weight and shakes the mower while in use.
Loose Blade
Blades can sometimes become loose. Once the blade is no longer seated correctly, it shifts its center of gravity. As a result, it will no longer be balanced. You could have a vibrating lawn mower, depending on how loose the blade becomes.
Debris Around the Crankshaft
Lawn mowers have a knack for picking up objects from around the yard. Unfortunately, these items often become entangled around the crankshaft and throw the mower out of balance as the shaft rotates. As a result, poor weight distribution will cause a vibrating lawn mower.
Debris in the Pulleys
A foreign object stuck in a pulley, such as a piece of mulch or a rock, will cause a bump each time it spins and contacts the belt. In addition, the high rotation speed will cause the mower to vibrate and potentially lead to the lawn mower shaking violently.
How to Reduce Lawn Mower Vibration (4 Steps)
With these four steps, you will find that you can eliminate the majority of lawn mower vibration problems. Let me walk you through the steps and tell you what tools you’ll need to stop the shaking and get your mowing back to normal.
Balancing A Lawn Mower Blade
First, you need to remove the blade from the lawn mower. Start by removing the spark plug and tucking it out of the way to avoid mishaps. Then, tilt the lawn mower over the correct way, so the oil doesn’t accidentally pour into the wrong engine parts. Next, take a blade brace or wedge to stop the blade from spinning and insert it into position. Using your wrench or ratchet, remove the bolt that secures the blade.
You can now test the blade’s balance with the blade removed from the lawn mower.
Place the blade onto your blade balancer and check the weight distribution. If you find that one side of the blade is heavier, you will know it’s out of balance and needs adjusting.
To achieve this, you must sharpen the lawn mower blade using the correct method to attain equal weight distribution. This will result in removing enough metal from one side of the blade to even out the weight of both sides.
Next, reinstall the blade using the same tools as before. Remember that the blade brace will need to be positioned this time to receive the blade rotating in the opposite direction.
Tools Required to Balance a Lawn Mower Blade
- Blade Sharpening Tool
- Blade Balancer
- Blade Brace
- Wrench or Ratchet
Tightening a Lawn Mower Blade
If your blade has come loose, then there could be an issue with the actual bolt. The continuous vibration of the lawn mower has potentially worn down the thread of the bolt and the bolt receiver. If this happens, the bolt will always loosen off with vibration.
First, remove the spark plug and tilt over the lawn mower. Next, remove the bolt using your wrench or ratchet and remove the blade. Then, thread the bolt back into the lawnmower ¼ to ½ inch and check to see that it is snug. If you find that the bolt can move backward and forward a little, you’ll want to replace it.
Next, take a thread lock adhesive and apply it to your bolt. This will compensate for any wear in the pulley/crankshaft thread. Continue by repositioning the blade and inserting the bolt. Next, place your blade brace into position, and use your wrench or ratchet to tighten the bolt.
I find it best to leave the lawn mower overnight so that the thread lock adhesive has plenty of time to cure.
Tools Required to Replace a Lawn Mower Blade
- Blade Brace
- Wrench or Ratchet
- Thread Lock Adhesive
- New Bolt
Removing Debris from Around the Crankshaft
Depending on the debris wrapped around the crankshaft and how tight it is will determine the tools you should use and the best approach to take.
Start by removing the spark plug and tilting over the lawn mower. If you find garden vegetation causing the problem, I would try unwrapping it if you can. Alternatively, using a pair of gardening hand shears will cut through the plant. A box cutter knife should do the trick if it happens to be something like a rope or garden hose.
Tools Require to Remove Debris from the Crankshaft
- Gardening Hand Shears
- Box Cutter Knife
Removing Debris From a Pulley
Removing debris from a pulley is relatively simple once you locate the intrusion. If you know where the problem lies, you can disconnect the spark plug and go straight to the problem. If not, then you may need to spin the pulleys.
With the spark plug disconnected, start by pulling the belt or spinning the blade by hand. This will turn the pulley and give you a good view between the pulley flanges. Also, you might find that the blade/belt gets tight once it hits the obstruction.
Once you find the obstruction, you can take a screwdriver and pop out the problem.
Tools Required to Clear an Obstructed Pulley
- Screwdriver
What About a Riding Lawn Mower Vibrating Really Bad?
Riding mowers are as susceptible to problems causing vibration as regular walk-behind lawn mowers. If anything, the vibration will be more noticeable since you sit on the mower, and they are generally bigger all around.
To reduce lawn mower vibration, you’ll need to be more vigilant with checking your mower. Riding lawn mowers have multiple blades, several pulleys, and additional moving parts such as adjustable cutting decks. As a result, these additional components increase the chances of picking up a problem. Thankfully, the fixes are quick and easy.
Hi Tom,
One type of blade imbalance that you don’t raise is the type of blade that I have on my push mower. It has two ‘swing’ blades at each end of the fixed centre blade/mount. Normally these are fixed in position, but occasionally pivot around their attachment and create imbalance.
A few taps with a hammer can bring the unruly blade back into alignment. Or if it’s actually come loose, retighten the attachment bolt.
I was all ready to wrestle with crankshafts, but lo and behold, hit it with a hammer and it’s fixed!
Hi Bob,
Honestly, I haven’t had much experience with balancing blades for lawn mowers with swing blades. They are not the type of lawn mower I come across. The only method I have seen when balancing swing blades is weighing each blade individually and sharpening each individually, so they each weigh the same. I would be interested to know what method you use. It seems like your hammer trick comes in handy.
Thanks for the comment!
Tom.
My John Deere riding mower began vibrating at the end of last year. Not just when I engage pro. It vibrates just sitting there without the blades turning. Any ideas?
Hi Joe,
The first thing I would check is the engine mounts. If you have a loose bolt or two or a worn-out engine bushing, the engine can rock and vibrate your lawn mower. If it’s not that, then I would be curious if your John Deere has a two-cylinder engine. If it does, then there could be an issue with the firing timing and the adjustment of the intake and exhaust valves.
I hope this gives you a few ideas.
Thanks
Tom.