Lawn mower upside down. How to Sharpen Lawn Mower Blades

How to Sharpen Lawn Mower Blades

Some time ago I was in a hardware store and an associate told me I should bring in my mower blades to have them sharpened as they “had a machine to make them razor-sharp.” I remember thinking, “Why would I want them to be razor-sharp? It’s a lawn mower for crying out loud. I’m not shaving with it. I am essentially trying to achieve the same look on my lawn as a pair of goats could do.”

So, here’s a quick article to show you how to sharpen your lawn mower blades to a reasonable honing. Considering you are cutting a plant which rabbits nibble, your 6.5 HP engine with blades spinning at 3,600 RPM is probably on the side of overkill.

How to Sharpen Lawn Mower Blades

There is one rule I always follow when dealing with sharpening blades of any type: Leather Gloves, Always! Whether you are using this technique on mower blades or a machete, put on a pair of heavy-duty leather gloves or some other kind of protection.

Tools You’ll Need

The tools you need. A metal file, leather gloves, and a vice.

  • Leather Gloves
  • Metal Flat File or Bench Grinder
  • Socket Wrench
  • Hammer\Mallet\Wood block
  • Bench Vice

Step 1: Turn the mower upside down and take the blade off

Some folks will tell you that turning the mower upside down is bad, as the oil will go to places it is not supposed to. I usually do this at the beginning of the season and my oil has already been drained. However, I have done this before with oil in the engine and as long as I let it sit upright and settle for a while, there have been no issues.

Use the socket wrench and appropriate socket to get the work done.

Hint: The bolt is screwed in like normal (righty-tighty, lefty-loosey), but since the blade also spins it can be a pain to loosen. I find it helpful to use a block of wood or hammer to hit against the blade while I hold the socket wrench (gloved of course), rather than trying to torque down on the wrench and a potentially sharp blade.

Turn the mower upside down, preferably after you have drained last years oil and gas. Remove the blade with a socket wrench.

This mower blade is pretty bad off.

Step 2: Place the blade in a vice and sharpen with a file

I have two types of blades for my different mowers: one is a mulching blade (with the extra curve) and the other is a regular blade. The process for sharpening either blade-type is the same.

lawn, mower, upside, down, sharpen

Run the metal file across the blade and away from you, at an angle, filing on the forward stroke as in the video and pictures shown below.

Note: If using a bench grinder, be careful how much metal you remove (See the next step on leveling). It can be easy to try to remove any imperfections in the blade which may remove more metal than necessary. This is fine as long as you keep both sides the same weight.

Run the file across the blade at an angle and away from you. Place pressure on the file on the forward stroke.

The angle of the file can be determined by the existing edge of the mower blade. Only one side needs to be sharpened.

Step 3: Repeat on the other side and check the balance

While I don’t believe your blade has to be razor-sharp to get the job done, it does need to be balanced. An unbalanced blade will lead to unwanted vibration and noise as well as increasing overall engine\mechanical wear. If you don’t have a handy tool for checking the level of your blade, just rest the blade across your finger, like checking the balance of a good knife. If you have severe leaning on one side, you will need to take off more metal, which means more filing.

Check the mower blade for levelness by using a tool which you can pick up at any hardware store in the mower section.

Step 4: Reattach the blade

Put the blade back on the mower the same way it came off. The concave side of the blade faces the grass. Be sure not to over tighten the bolt; you’ll have to do this again next year!

Happy Spring!

Which Side Of The Lawn Mower Blade Is Up? (2023 Guide)

Owning a lawn mower is a great way to save some money and maintain more control over your lawn and yard. But, it can come with some unexpected maintenance, and it’s alright if you don’t already know how to keep your lawn mower in good condition.

If you want to keep your lawn mower working well, you need to know how to install your lawn mower’s blade.

Don’t worry if you’ve looked at lawn mower blades and been completely baffled by them before.

I wrote this guide because I’ve been there, and I know how important proper blade installation can be. After all, getting the installation right is critical for the life of the blade, the function of the lawn mower, and the appearance of your lawn.

In this guide you’ll learn:

  • Why lawn mower blade direction matters
  • How to tell which side of your lawn mower’s blade is up
  • And much more!

Why Does It Matter Which Side Of Your Lawn Mower Blade Is Up?

If you’re in a hurry, this video will help explain why it matters which side of your lawn mower’s blade is up, why it matters, and how to install the blade.

Use the Cutting Edge

Most walk-behind lawn mowers rotate the blade to the right, or clockwise. That means that when the blade is spinning, the cutting edge should spin to the right. However, this isn’t 100% foolproof.

Some lawn mowers do spin counterclockwise. It’s rarer, but you have to know which direction your lawn mower spins to be sure. Your lawn mower’s user’s manual should be able to tell you which direction the blades spin.

The Wings Face Up

On most lawn mower blades there will be a small part of the blade that isn’t flat, but angled up. This little wing on the blade is designed to encourage air movement, helping pull your grass upward for an even cut.

The wings on lawn mower blades are always designed to point up toward the lawn mower’s cutting deck. The same is true for the more extensive wings on mulching blades. If your lawn mower blade has wings, those wings should point toward the lawn mower and away from the grass.

Those three techniques should help you figure out which side of the lawn mower blade is up on pretty much any lawn mower blade. Assuming you know which direction your lawn mower spins the blade, that is the most fool-proof method, but the other two options are usually easier and faster ways to tell.

How To Tell What Kind Of Lawn Mower Blade You Need?

There are two basic kinds of lawn mower blade to choose between, and getting the right one can make a significant impact on your lawn mower’s performance. Most lawn mowers are compatible with both types of blade.

It’s important to remember that not all blades are created equal, and just because a blade is the right length doesn’t mean it’s compatible with your lawn mower. You always need to check your lawn mower for which blades are compatible.

Regular Lawn Mower Blades

Regular lawn mower blades are the simplest option. They are blades that are designed to get the job done without any bells and whistles or extra functions. These blades leave clippings relatively long, but they can also provide a more even mow than more complicated blades.

It’s important to have a good cutting edge on these blades since they are really reliant on cutting power to get good results.

Also called standard or medium-lift blades, these blades are typically on lawn mowers with side-discharge designs.

High Lift Blades

High lift blades are generally used for lawn mowers that have a bagging function because they provide more airflow that helps to move the grass clippings into the bag. These blades also provide higher suction, which means that they cut the grass at a more consistent height by pulling the grass up straighter.

Mulching Blades and Gator Blades

Mulching blades and gator blades both provide even more suction and cutting power in order to process the grass into smaller pieces. Of the two blade types, mulching blades are gentler. They process clippings into smaller chunks to distribute back over your lawn to act as a protective layer over the top soil.

How to Sharpen Lawn Mower Blades | Tutorial from Gardening Products Review

However, mulching blades are not typically a good idea if you’re trying to bag your grass clippings at the same time. They just don’t move the clippings toward the bag very effectively.

Gator blades process the grass clippings even smaller than mulching blades. They are designed to get the clippings small enough to eventually mix into the top soil of your lawn where they will decompose and replenish the soil.

My Final Thoughts On Which Side Of The Lawn Mower Blade Is Up

Knowing which side of your lawn mower is up might seem like a simple thing, but it’s incredibly important. Choosing the right side of your lawn mower blade will help maintain the health of your lawn and can even reduce the maintenance on your lawn mower itself.

lawn, mower, upside, down, sharpen


Learning how to install your lawn mower’s blade properly shouldn’t be difficult, but it is an important step if you want to keep your lawn mower in good condition. Hopefully this guide will help you decide which kind of blade is right for your lawn, and learn how to install it successfully.

Which Side Of The Lawn Mower Blade Is Up?

You are probably wondering how to tell which side of your lawn mower blade is up. We have researched all about lawn mower blades for you.

In order to figure out which side of a lawn mower blade is up, you should be able to recognize what side of the blade is sharp and which side is dull. Whichever side of the blade that is sharp is the edge that does the cutting. The sharpened side faces the ground as to cut the grass successfully, and the dull edge faces the lawn mower’s deck.

Keep reading to learn more about how to determine which size lawn mower blade you will need, which direction your mower blades spin, what happens if you install lawn mower blades upside down, and how to sharpen your mower blades.

Lawn Mower Blades

Another way to figure out which side of your lawn mower blade is up is to look for a stamp, sticker, or writing etched into the blade. Most blades that are new have a sticker or writing etched into the blade stating which side is down. The two most common phrases etched onto blades are “This Side Down” and “Toward Grass.” Look for one of these phrases to help you understand which side is up.

If you are having difficulty determining which side of the blade is sharp and which side is dull, the ends taper and should point upward.

Lastly, you can always check your manual to help you figure out which side of your lawn mower blade is up. If one of your blades seem damaged with large dents or chips, it is probably time to replace it. Investing in new mower blades will help your lawn mower preform more efficiently.

Types of Mower Blades

2-in-1 blades, which are standard, are made to cut grass in such a way that the aerodynamics cause the cut grass to powerfully eject the clippings out from under the deck of the lawn mower. This happens so that the cut grass does not clump up under the lawn mower causing it to become compacted. Lawn mowers are designed to have the clippings discharge from the side of the deck or to fill an attached removable bag. The removable bag makes disposing of the clippings easier.

The other most common type of lawn mower blade is the “mulching blade.” These are referred to as 3-in-1 blades because they perform a unique action. 3-in-1 mower blades do what standard blades do in addition to a third feature. They can also shred the grass clippings into a desirable fine mulch to be left on the lawn almost unnoticeable.

Mulching blades look different than standard lawn mower blades. The cutting edge of a mulching blade has points on one side. This points should face the sky. If your blade does not already have a sticker or etched words indicating which side is up or which side is down, we suggest you add a sticker and label it.

Mulching your grass is environmentally friendly, but can cause your mower to become clogged under the deck of your lawn mower. This is especially true if the grass you are cutting is overgrown or wet at the time.

How do I know which size lawn mower blade I need?

The three things you want to check when sizing your lawn mower blade are the length, width, and placement of the center hole. The space between the outer holes and thickness are two more essential measurements to note when choosing the right lawn mower blade for your mower. When you measure the length of your existing blade you measure diagonally from one tip of your blade to the tip on the opposite end.

Typically lawn mower blades measure between 16.75 inches and 22 inches. Even if your original lawn mower blade is 18 inches long, the majority of lawn mowers can accommodate 21 inch blades. You do not want to install blades that are smaller or shorter than the original blades.

Which way do mower blades spin?

Characteristically lawn mower blades rotate clockwise if you are thinking of which direction from standing up looking down at the deck. If looked at from underneath, the blades spin counter-clockwise. Checking to see which side of the deck the discharge chute is on is an indication of which way the blades spin and cut.

If the discharge chute is on the right side, the blades turn clockwise. If the discharge chute is on the left, the blades rotate counter-clockwise. They are built this way so that the blades spin in such a way that they help guide the blades of grass to be released out of the chute.

What happens if you install lawn mower blades upside down?

Theoretically if you were to install your mower blades upside down, they would not cut the grass. If the blades are installed upside down, the sharp edge would be facing the deck of the lawn mower rather than the grass.

This mistake can also damage your lawn mower. It is a potentially dangerous and costly mistake. Refer back to our answer on how to determine which side of your blade is up before the installation process.

How to sharpen lawn mower blades?

After you have figured out which side of your lawn mower blade is the sharp edge, you will know which edge to sharpen. If your blade has become dull before you check, understand that the cutting edge faces the grass, therefore, it will be the side that needs sharpened.

There are several methods for sharpening lawn mower blades. Some lawn mowers are put together in a way that you can sharpen your blades without removing them. It is usually necessary to remove the blades in order to sharpen them. You can do so by using a bench grinder, hand file, rotary tool, or angle grinder.

Some tips and tricks for sharpening your mower blades are to understand that eventually your mower blade will become thin and need replaced, but until then sharpening the blades will make your lawn mower last much longer and preform proficiently. Doing this will help cut down your mowing time. It also helps ensure you will end up with a nice evenly cut lawn.

In order to prevent grass from building up under the deck of your lawn mower, you can spray the underside with non-stick cooking spray or Teflon spray. It is important that blades are tightly secured. With the spark plug wire disconnected, you can attempt to wiggle each blade. If the blade wiggles, it needs to be tightened. A socket wrench should do the trick.

You do not need to sharpen your blade to such a sharp edge that it will cut your hand. Grass is not nearly coarse enough to need your mower blades to be quite this sharp. You do want to be sure to sharpen each blade similarly so that they are balanced when re-attached.

Although a file, rotary tool, and bench grinder will work for sharpening your mower blades, using an angle grinder is the fastest easiest method. Multi-functional sharpening tools are available for purchase as well.

How Often Should I Sharpen My Mower Blades?

A good rule of thumb for deciding when to sharpen your blades is to do this about every 20 to 25 hours of run time. How often you need to sharpen your blades is determined by how often you mow, and how long it takes you to get the job done. You can repeat this process five to ten times or more before needing to replace your blades. High-quality blades last even longer!

In Closing

To determine which side of your lawn mower blade is up, first figure out which side is the sharp cutting edge, and which side is the blunt edge. Look for a sticker indicating which side goes up and which side faces downward. The cutting edge should face the grass while the dull edge should face the deck of the mower.

If you would like to learn more about lawn mowers and sharpening lawn mower blades check out the links below:

Why Does My Lawn Mower Rev Up And Down Then Die? 5 (Simple) Solutions

So you are here because you want to know why your lawn mower revs up and down, and then dies?

Or maybe the engine is just revving up and down without dying?

Either way, it is an annoying problem to have but the good news is you can usually fairly easily pinpoint what is causing the issue.

And normally it is pretty easy to fix as well.

So let’s take a closer look at how to remedy this problem.

Why Does My Lawn Mower Rev Up And Down Then Die?

If your mower is revving up and down and/or dying, you should check for any clogged components. Most notably this will be the air filter and carburetor, or the diaphragm in the carburetor might simply need replacing. Also, check the spring attaching the governor to the throttle, and make sure your gas isn’t water contaminated.

Just for information, you might have heard this problem called several other things. Sometimes it is referred to as a lawn mower hunting and surging, sometimes as RPM hunting, sometimes as governor hunting, and sometimes simply just surging and revving.

They all mean the same thing and can all be resolved in the same way.

ISSUE #1: Check the Air Filter

The first place to start when trying to determine why your mower engine is revving up and down is to check the air filter.

A dirty or clogged air filter can cause the fuel mixture in the mower to be too rich.

That is because if your air filter is clogged up, it means there is more gas in the carburetor than normal.

All you need to do here is replace the air filter. This is a pretty easy job and the reason why it is the first thing you should check.

ISSUE #2: Check the Carb

The root cause of any engine hunting and surging often involves the carburetor.

An air leak to the carburetor, an incorrect air-to-fuel mixture adjustment or a dirty carburetor can all be to blame.

often than not it is the last of these that is causing the problem. Dirty, clogged jets in the carb, starts off a chain reaction.

The clogged jet means that the engine is not getting enough fuel, the RPM drops, the governor opens the throttle, air and fuel rushes in, the engine surges then drops, and the cycle is then repeated.

To fix this you simply need to clean out the clogged-up jet. Don’t do this using wire as you could damage the jet, instead buy some dedicated carb cleaner or gives it a blow with some compressed air.

It could also be that the rubber diaphragm in the carb needs replacing, as this is how a lot of smaller engines regulate fuel pressure.

When these diaphragms get old they can often dry out and stop working. A new diaphragm should not cost any more than 10, make sure you have the correct model and number to order the right diaphragm as there are more than you would think!

Sometimes the needle valve on the diaphragm can get stuck too. Adding a little seafoam to the gas tank will often loosen the needle.

Some particular brands are more prone to problems with the carb than others.

If you have a carb on the tank Briggs and Stratton engine that is revving up and down, often it is because the carb diaphragm is getting old and brittle and needs replacing.

Honda builds solid motors, but their carburetors are very finely engineered and very sensitive to gas quality.

If the engine of your Honda lawn mower is revving up and down you might want to disassemble and clean the carb.

Or you could try dropping the float bowl and loosening the vertical jet from below. Then blow it with some compressed air to clean it and reattach.

There is also the option for any of these issues of simply replacing the carburetor. They are fairly inexpensive and can be replaced by a professional if necessary.

ISSUE #3: Check the Governor

Most small engines are equipped with a governor. This stops the engine from over-revving by reducing the carburetor’s throttle opening

Essentially it is there to govern the speed of the engine, and keep it running at a safe speed.

lawn, mower, upside, down, sharpen

The governor is an air vane that is attached to the throttle wire by a spring, this spring brings the engine back to neutral.

As the engine runs faster, the air from the cooling fins on top of the engine pushes against the air vane. The air vane move the throttle and slows the engine down.

Then as the air decreases the spring reopens the throttle and the engine RPMs increase.

So a lawn mower engine that is continually hunting and surging, indicates there could be a problem with the governor.

And more often than not it stems from the spring that connects the governor to the throttle.

If the spring is dirty, weak or damaged in some way, or has worked itself into the wrong place the governor will not be able to regulate the speed of the engine effectively.

Check the spring to see if it is broken, and move the throttle shaft in the carb to see if it is sticking.

Replacing the spring usually solves the problem.

ISSUE #4: Check the Spark Plugs

Dirt in the spark plugs can cause them to lose contact with each other and misfire.

This could not only make the engine surge, but it could also lead to excessive wear on pistons or valves.

Take a look and replace them if necessary.

ISSUE #5: Has It Been in Storage For a Long Time? Check the Fuel…

Have you just got your mower out for the season? Is it revving up and down?

The ethanol in modern gas is notorious for attracting water. Water sinks to the bottom of the fuel tank, where it gets sucked into the carb and through the engine.

Even just a small amount of water can cause problems for a lawn mower engine.

lawn, mower, upside, down, sharpen

You will need to get rid of the bad gas and possibly clean the carb too.

Using ethanol-free gas and mixing in some stabilizer should eliminate the chances of this happening again.

How to Fix a Surging Engine: An Overview

Hopefully if you have turned on your mower only to find it constantly revving up and down/hunting and surging and also possibly dying, then this has helped you solve that problem.

Start off by checking the air filter, as that can often be the cause, and if it is it is one of the easiest and cheapest parts to replace.

If that doesn’t solve it, the two main parts to check are the carburetor and the governor.

Often water contaminated gas can be the culprit as well, especially if you don’t use ethanol-free gas.

Either way, I hope this hopes you solve the problem and you are out there mowing your lawn in no time!