Why is my lawn mower shaking?

It's normal for a rotary lawn mower to vibrate when in use, but if the vibration seems excessive there may be something wrong.

Excessive vibration not only makes a lawn mower uncomfortable to use, but if left unchecked can lead to further damage and can be dangerous. If your lawn mower is shaking or vibrating excessively it should be investigated and rectified before grass cutting continues.

3 Possible Causes of Excessive Shaking or Vibrating

Unbalanced blade

The most common cause of excessive vibration is an unbalanced blade. If you've recently had your blade sharpened, it's possible the blade hasn't been properly balanced during the sharpening process.

To fix this, the blade should be removed, rebalanced and refitted.

Damaged blade

If your blade has come into contact with an object whilst mowing, perhaps a drain cover, a large stone or the corner of a patio, your blade may be damaged or bent. A bent blade will be unbalanced which will cause your mower to shake.

If damage to your blade has occurred, it's possible that your crankshaft was also damaged during the impact.

A damaged mower blade should be replaced and your crankshaft inspected.

Damaged crankshaft

The crankshaft comes out of the bottom of a petrol engine to which the blade is attached. If your blade has come into contact with something whilst mowing, it's possible the impact has damaged your crankshaft.

If your crankshaft is damaged or bent this will cause your mower to vibrate. In order to repair an engine with a bent crankshaft the engine must be stripped down and the crankshaft replaced.

Important Safety Warnings

If you intend to examine the underside of your mower, remember to ensure that an electric mower is unplugged or the spark plug cap is removed from a petrol mower to prevent the mower starting accidentally. If your mower is cordless you should remove the battery. Remember also that blades are sharp!

Always consult your owner’s manual for instructions on the correct way to tip a petrol mower to prevent petrol leaks and other potential damage.

Any of the faults listed above should only be rectified or undertaken by a competent person with the appropriate tools and training, whilst following all applicable health and safety guidelines.

If you don't feel comfortable or would like an expert opinion, our service team will be happy to help you.