How to tell if lawn mower crankshaft is bent

It is seen that in lots of time your lawn mower crankshaft got bent. There may be many reasons behind it. Now the question is how can I understand that my lawn mower crankshafts got bent. No worries. The steps to determine whether your mowers crankshaft is bent or not is pretty simple and straight forward. You can do it easily.

In this article, I will be talking about the ways following which you can understand whether your mowers crankshaft is bent or not.

What are the causes behind a bent crankshaft?

It is better to know the reasons first that cause a bent crankshaft. In most of the cases, the lawn mower crankshaft got bent once it hits an obstacle that can’t move like a large rock, pipes, stumps, sprinklers and so on. Without it, there are some other reasons like improper handling during maintenance or dropping the crankshaft while installation.

How to determine whether my lawn mowers crankshaft is bent?

Well, you can go for searching the symptoms or physical inspection to identify the sign of disfiguring. Let’s start with searching for the symptoms.

1. Searching for the symptoms:

While searching for the symptoms, you have to pay attention to two issues. They are Excessive vibrations and Transmission issues.

Excessive vibrations

If you find that your mower is generating grinding sounds and vibration at a high rate, then there is a possibility of getting your shaft bent. You will hear the noise within just a few seconds before it starts running free. So, you should look for unusual and loud sounds coming out of the lawn mower.

Transmission issues

Well, you know that the lawn mower is operated by an engine. It may get transmission issues. You may find your mower is having problems while starting up and running. These are the common issues your mower crankshaft faces. Whatever it is not impossible that your shaft messing up the ignition or hits the flywheel as well.

2. Physical inspection:

However, there are few methods of physical inspection following which you can tell whether your mower shaft is bent or not. No worries. Here, I will talk about all methods.

Inspection method 1

Well, while following the first method, you should get started by making the spark plug disconnected and turning the mower over. Then, use a marker for marking one end of your mowers blade. Without it, you have another option to clamp a ruler from your mowers edge to the touching point of rulers and crankshaft.

After that, you have to turn the crankshaft manually once you feel that gap between the rulers’ end and also the crankshaft through a single rotation. You should wear a pair of safety hand gloves while doing this.

If you find the gap expands first and then contracts, then you have to understand that your shaft is deformed.

Inspection method 2

In this method, you have to start by removing the spark plug from your lawn mower. Then ask help from someone for pulling the starter cord of your mower. While doing this, you have to keep your eyes on the bolt attentively that will hold the blade and check for any wobbles. If you find any bolt moves or wobbles from a side to another side, then you have to understand that your crankshaft is bent.

Inspection method 3

Well, while following this method, you have to park the lawn mower on a flat surface where there is no debris. You should leave the engine running along with the blade engaged. Then, go through observation of whether there is any sign of blade shaking. The wobbly blade often does harm to itself but it can be the signal of a bent crankshaft.

Inspection method 4

In the present time, most of the lawn mowers come with a feature using which you can easily verify whether your shaft is bent or not. If your lawn mower holds this feature, then you can use the dial indicator. It will tell you everything. Not all of the lawn mower holds this feature.


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