Are Lawn Mower Blades Reverse Threaded?

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Lawnmowers are excellent garden or outdoor tools that help lawn owners to maintain their lawns and cut grass neatly. Just like any machine that you’ll find, lawnmowers also require regular care and maintenance, and removing the mower’s blade for the purpose of sharpening or replacement is one of the major maintenance tasks.

Typically, most blades found on walk-behind lawnmower models are held in place by a threaded hex-headed bolt that screws into a blade adapter fitted onto the engine’s driveshaft. Whenever your mower blade needs to be sharpened or replaced, it is necessary that you turn out the blade retaining bolt in order to get the blade off the mower.

Are Lawn Mower Blades Reverse Threaded?

Yes and no. The lawnmower blades itself is not threaded, but most nuts that held the blade in place are reverse threaded. The reverse thread helps to secure the blade on the drive shaft such that the rotation of the blade does not loosen the nut. It is important to note that not all lawnmowers use a reverse threaded nut.

Are Lawn Mower Blades Reverse Threaded? 1
(CC BY 2.0) by somegeekintn

There are still a lot of details to pay attention to in order to carry out the procedure easily and correctly.  In this article, we’ll be showing you the complete step by step process on how to do it safely. It’s safe to say that the last thing anyone would want is to be in a hurry to quickly get the blade off, only to end up injuring themselves. This actually happens more than you may think. Follow closely in the rest of this article to find out all you need to know about this topic.

How Do Lawnmower Blades Work?

One of the most interesting features of lawn mowers is undoubtedly their blades which are responsible for cutting the grass neatly. Also, these blades are the major feature that catches our attention when we’re purchasing the equipment or when we consider a functioning lawn mower. So it is quite obvious why the blades are very important and have become a topic which many pay close attention to. In fact, you’ll find various thesis about the blades, and why their incorporation to the internal combustion engine has become very vital in differentiating the different types of lawn mower that there are.

That being said, threading is a crucial aspect that helps in the movement and rotation of the blades. For all such rotating objects generally, the threading is designed in such a way that every rotation tightens the nut to ensure that the blade remains firmly attached and intact with the frame. It simply works by turning the center of the blade opposite to the normal cutting rotation. There is a securing nut that is specifically provided for this purpose. It is also important to note that loosening refers to a right-hand thread which is done in the clockwise direction while tightening is the left-hand thread which is done in a counter-clockwise direction.

Are Lawn Mower Blades Reverse Threaded?

Generally speaking, most lawnmower blade nuts are reversely threaded to firmly secure the blade onto the drive shaft of the engine. This simply means that when the blade rotates, the bolt is not loosened or affected. It is worth remembering that not all blades are designed with a reverse thread bolt to secure them. So when you want to sharpen or replace your mower blade, it is important that you first find out the direction of shaft rotation. By doing this, you’ll be sure that the blade’s rotation won’t end up loosening the nut.

You’ll find that the blades on many walk-behind lawn mower models rotate to the right when you are mowing (that is, the clockwise direction). To remove the blade on this type of mower, the blade’s retaining bolt should be turned to the left or counterclockwise direction. Before unbolting your blade, make sure you tip the mower on its side with the engine air cleaner facing upward, then block the blade with a piece of wood so it won’t turn while you’re working. Also, make sure the bolt is kept in a safe place so that you can easily locate it when it’s time to return the blade.

Most times, the blades of a lawn mower are reverse-threaded. However, you may be required to block the blade from turning in order to break the bolt loose. Removing your blade for sharpening or replacement will require the use of a socket wrench to unbolt the lock nut, which is often reverse-threaded. Also, it is important to follow the safety instructions for your particular lawn mower which is usually found in your user manual. Wear protective gloves to shield your hands from cut or injury, and follow all instructions properly.

How to Remove the Blade Safely

Step 1. Disconnect the ignition wire:

The first thing to do is to disconnect the ignition wire from the spark plug. If you’re using a cordless mower, remove the battery pack. This is to prevent the risk of the engine accidentally starting up while you’re working. You should also drain the gas tank so it won’t spill any fuel while you’re working on the blades. To disconnect the spark plug, locate the spark plug boot, which is usually found on the front side of the engine. Firmly pull the boot to disconnect it from the spark plug. No extra tools are needed for this step as you can simply use your hand.

Step 2. Tip the mower:

Tip the mower on its side, with gas tank and air cleaner facing upward in order to prevent spillage, and to expose the nut or bolt that secures the blade to the mower.

Step 3. Retain the blade from moving:

Wedge a short wood block between the end of the blade and inside surface of the mowing deck to keep the blade from turning accidentally. Then use a wrench and socket to loosen the nut or bolt. To increase the leverage when loosening any stubborn fastener, you can slip a longer bar over the wrench handle.

Step 4. Note the blade position:

Remember to make a mental note of which side of the blade faces downward. It’s important to bolt back the blade in the same position as it was removed. When breaking the bolt loose, you may need to apply a bit of force, but be sure that you don’t slip and cut your hand. Using a breaker bar will help provide an extra force while safely loosing the bolt.

Step 5. Remove the blade:

Loosen the bolt by turning left (counterclockwise) using a 16mm socket. However,  depending on the model of your lawn mower, the bolt head can be 1/2″ inch or 5/8 inch.

To have more leverage, you should make use of a bigger socket wrench. As you turn the socket, the blade bolt will also turn, although you may be required to hold it with your hand while loosening it. This is why it is important to wear gloves while working to protect your hands from injury. It is also worth noting that some models of lawn mowers use a blade-lock tool to keep the mower in one place. These tools will prevent the blade from rotating when you’re trying to remove the bolt.

It is not uncommon to see the nut get smaller due to corrosion, hence, you should make use of an appropriate tool. For instance, a 16 mm socket may be a better fit for an 18 to 20 mm bolt due to the reduction in size. Next, you should look for a breaker bar to help with leverage. If you notice that the tension suddenly becomes soft, it may be the bolt stripping the threads and not that it is loosening. This is why the wearing of gloves should be taken seriously to reduce skinned knuckles. Finally, be sure to fit the replacement blade into the blade adapter, making sure that only the correct side is facing up. Also, replace the washers in the right order. Then tighten the blade retaining bolt by turning it clockwise or to the right, using the torque value that is specified in your user manual. We hope that this piece has been helpful. Good luck.

Step 6. Clean the Mower underside:

This step is optional, but once the blade is removed, try to scrape clean the underside of the mowing deck to remove all caked-on debris and grass. You can use a narrow-blade putty knife to get better results.