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How to Tell if Lawn Mower Crankshaft Is Bent

A lawn mower is a device that is used to cut grass, or in some cases, weeds, with a rotating cutting blade. It uses one or more blades to cut grass.

They usually have blades that are powered by an engine, and they are designed to cut the grass at a certain height to avoid accidentally hurting people and pets.

Some lawn mowers have a single blade while others have two or more blades. Sometime these machines get serious problem like crankshaft bent.

The crankshaft of the engine is located near the engine of the mower, and it converts a linear motion to a rotational motion. The crankshaft is connected to the flywheel via a coupling that allows power to be transferred from the piston’s action.

This will then produce rotational motion in the flywheel and its attached gear, which will drive an output shaft for propulsion. In this article we’ll discuss the reasons behind crankshaft bent and some of the possible fixes.

We’ll also discuss how to identify a bent crank and what precautions to take before trying to fix it.

Bent crankshaft of a lawn mower
Bent crankshaft

What is the crankshaft in a lawn mower?

A crankshaft is a rotating shaft that sits in the center of the engine and transmits torque to the flywheel. It is a critical part of starting the engine, taking the up and down motion of the pistons.

The crankshaft is one of the most important parts of a lawn mower. It is responsible for taking the up and down motion of the pistons. It takes power from the flywheel to which it’s attached.

The crankshaft rotates around an axis, and it powers the fan belt and the transmission. This enables mowers to run more smoothly in outdoor environments with high grass.

Reasons why the crankshaft can bent

The crankshaft is one of the most important parts in a lawnmower. It is responsible for transferring power from the engine to the blades of the mower.

The blades rotate around it and cut grass into tiny pieces that are fed into the engine’s combustion chamber where they are burned. The most common issues with a bent crankshaft are hard to start and excessive vibration.

Checking for a bent crankshaft
Checking for a bent crankshaft

Hard to start means when you try to start your lawn mower or engine and it won’t start because something was wrong with the crankcase or cylinder head gaskets in order for them to be able to seal properly.

Excessive vibration can be caused also. When a crankshaft bends, it can also make uneven cuts, transmission issues, or grinding noises.

Excessive vibration

If the blade of a lawn mower vibrates too much, it can damage the crankshaft. As a result, the blades will not be able to turn properly, and the engine will not be able to produce enough power.

To avoid this, you have to make sure that the crankshaft is balanced and safe. The excessive vibration indicates a bent crankshaft on a lawnmower.

This means that blades are unable to turn properly into resistance and provide enough power for the engine to run efficiently.

If you detect any problem with your lawnmower’s performance or find your grass is poorly cut, there are some simple ways that you can fix this issue without having to head out for repairs or replacement parts.

Grinding Noises

One of the most common problems that can occur with gas mowers is when the crankshaft gets bent out of shape. This can be caused by a multitude of factors, such as excessive mowing and poor maintenance.

There are also many other issues that can arise if the crankshaft gets bent, such as strange grinding noises. The noise is caused by grinding of metal against metal and can be attributed to a number of reasons.

It makes the sound as you turn the handle to start the engine or any unusual noise or vibration while mowing.

Uneven cuts

Most mower blades are designed to cut grass at a horizontal angle. But if the crankshaft on your mower is bent, you may notice uneven cuts. This is caused by the blade spinning at high speed and cutting your lawn at an angle.

If your lawn mower blade is spinning unevenly at high speed. This can cause the blades to cut unevenly. You should check your lawn mowers crankshaft periodically to make sure it is functioning properly and not causing any problems.

Hard To Start the Mower

If you are experiencing a hard time starting the mower, it could be caused by a bent crankshaft. The direct symptom of a bent crankshaft is the mower cutting out shortly after starting.

If your lawn mower has a flywheel or flywheel key, it could also be that these are damaged. But the most likely cause is bent crankshaft.

Transmission issues

If the transmission of your lawn mower is not working properly and you cannot start it, it indicates a bent crankshaft. The engine’s speed is determined by crankshaft, flywheel, and ignition timing.

When these parts are damaged, it will result in problems running and starting up. The crankshaft bent can prevent the flywheel from turning and make it impossible for ignition timing to catch up with engine timing.

There are a few things to check before thinking of replacing the engine. Make sure that the crankshaft is clean and free of any dirt or debris, and it is not bent. This will ensure that it is spinning easily.

It should also be in good alignment with the flywheel. If those two are in line, then chances are that your engine is fine; you just have a broken transmission.


A crankshaft is bent in the lawn mower is a serious problem. The mower produces an uneven cut and makes grinding or noisy sounds. It is hard to start means it turns over but not starts because of the bent crankshaft.

Some of the common problems that might occur with a bent crankshaft are transmission issues, and excessive vibration. If you experience one of these problems, it is time to fix the issue before it gets worse.

You might try to straighten the crankshaft using proper method.

Straitening a bent crankshaft
Straitening a bent crankshaft

A bent crankshaft can be very risky and damage other components. It’s very hard to replace and costly too. So, finally if you find it is very hard replace it, then buying a new mower is a good idea.

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