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When to replace lawnmower blades?

The sharpness of lawnmower blades is essential to get a straight and nice cut lawn. Blade sharpness might not mean much for some owners. After all, even dull blades can cut grass. But they do not give the result you are looking for. Worn blades result in roughly and uneven cut grass that provides the lawn with a less maintained look, and the torn grass tips will turn brown quicker. Sharp blades not only cut cleanly but quickly, too, making the gardening routine simpler. Dull lawnmower blades can be sharpened, but once they become too dull and blunt, they have to be replaced.

When to replace lawnmower blades:

Knowing when to replace the lawnmower blades partly depends on the user’s judgment. Dull blades can be sharpened, but after a while, this will get harder and harder. They will become dented and chipped due to small stones and other debris, and sharpening is no longer possible. When a blade hits a rock and is chipped and dented, it is also better to replace. Besides inspecting the blade itself, these two factors can also help you judge the quality of your mower blades:

  • Evenness of the cut grass
  • Cleanliness of the cut grass
(CC BY 2.0) by Andy Mabbett

When mowing, carefully inspect the grass behind you. Unevenly and uncleanly cut grass is a good indication that the blades are not at their best. The best practice would be to sharpen the blades several times and then replace them.

Judging the Blade Condition:

Shredded grass and debris get caught in the cutter area of your lawnmower every time you mow. Before parking the mower in your garage, clean the blades and the cutter area. This will ensure that grass debris is not piling up in the cutter area and give you a chance to inspect the blades for their sharpness. You should also inspect your lawn to get an idea of the blade condition based on the grass quality. Our advice: Check these things every time you mow:

● Grass length and its evenness:

The main thing to look for is the evenness in your grass. Your grass should be cut at the same length with each pass of the mower. If this is not the case, and the grass looks uneven after completing one trip, it means the blades are not functioning properly.

● Grass edges:

The second approach for deciding if it is time for you to sharpen or change the blades is to examine the grass edges. If the grass tips are torn and not neatly cut, it is the right time for sharpening or replacement. Torn grass tips can affect grass wellbeing, making the grass turn dark quicker. Uncleanly cut grass can increase the chances of a pest attack too.

● Blade condition:

You can also inspect the blade itself. Look for chips or dents on the cutting edge. Inconsistencies in the blade are likely to roughly tear the grass rather than give it an even cut. Also, check the thickness of your lawnmower blade. Over a long period of use, dirt, sand, and other debris can erode the blade. Dull blades can be sharpened, but dents and chips on the blade’s surface reflect poor metal health, indicating that sharpening won’t do any good; the blades need to be replaced.

Sharpen the Blades, or Replace Them?

If you are on a tight budget, you will probably go for the sharpening option and will not be easily convinced to replace the blades. But replacement is the only option when the mower shows show signs of irreparable damages, which include:

  • Bends in the blade
  • Cracks on the blade surface
  • Worn surface and edges

These are the conditions in which you must replace the blades because there will be no benefit in sharpening them. Yard debris wears down a blade over the years, resulting in thin, weak metal (cracked mower blade). If your blades are worn thin, replace them immediately to avoid breakage. If blades break while you are mowing, they can cause injury.

Besides, it is recommended you should also not wait for your blades to go bad beyond repair to get a replacement. Having many substitution cutting edges close by is helpful, especially if you need to utilize the sharp edges for various purposes.

Other Sources of Blade Damage:

The blades of your lawnmower rotate at a very high rpm. If the blades hit a rock or toy during operation, they can get damaged severely. So, if you hear the sound of something hitting the blades, immediately stop the mower and search for scratches on the sharp edges. Check if the cutting edge is twisted or crooked. Twisted blades are not efficient and must be replaced.

Corrosion can also be a source of blade damage. Rusted blades need to be cleaned with a metal file. If the rust layer is too firm and thick, the blades should be replaced.

The Balanced Approach:

Eventually, the best practice would be a blend of sharpening the cutting edges now and then and keeping a substitution set at hand.

Regularly sharpening the blades will keep them from going to the extent of becoming faulty beyond repair. You can sharpen the blades yourself and don’t need to carry the mower to a mechanic’s shop. A metal file or a grinder can be used for sharpening. You can find a good lawnmower blade sharpening tutorial here to help you through the process.  

It is also quite helpful to utilize one set of edges for customary cutting and another for mulching in the fall. Since mulching reprocesses grass clippings into fine pieces, it wears out a cutting edge. Having one set committed to mulching keeps the other set sharp more.

How to Replace the Blades:

Just like blade sharpening, you can perform the replacement procedure yourself. The replacement set should be like the one being replaced, in diameter and thickness. Consult the user manual for the right blade specifications for your lawnmower.

Here’s a simple, step by step guide on how you can replace your lawnmower blades:

● Step 1: Seal the tank/cut the power

Make sure you have safety gloves on before performing the replacement procedure.

Remove the gas tank’s lid and place a plastic bag over the gas can’s top, sealing it. After doing this, replace the lid in its previous position. This will make sure that no gas spillage occurs while the mower is tilted.

If you are working on an electric mower, make sure it’s not plugged in.

● Step 2: Tilt the Lawn Mower

Park the mower on an open flat area with the parking brake applied. Tilt the mower to access the blade. When you tilt the mower, make sure that the fuel tank and the carburetor are on the top side to avoid any leakage.

Place a wooden block diagonally at the lawnmower’s far side to make it more stable in the lifted position.

● Step 3: Remove the Assembly:

Use a socket wrench to loosen and remove the nut holding the blade in place. Turn the wrench counterclockwise to loosen the nut. Before removing the blade, please take a picture of it on your phone. This will help you later to put the replacement set in the correct position.

● Step 4: Install the New Blade Set:

Refer to the photo you took and install the new blade set. The direction of the cutting edge is crucial and should match the photo. Consult the manual for the correct cutting edge direction for your model.

Use the socket wrench to tighten the nut, turning it clockwise this time. The nut should be tight, or else the blade would vibrate and not cut properly.

● Step 5: Finishing:

Once you have completed the sharpening process, lower the mower slowly. In case of a gas mower, reopen the mower fuel tank lid, remove the plastic bag, and put the lid back again. This step finishes the replacement procedure. Your mower is now equipped with a fresh set of sharp blades and is ready for the action.

Precautions and safety:

  • Make sure to wear protective gloves to avoid injury from sharp edges.
  • Make sure that the blade replacement doesn’t mess with your mower’s warranty. Check the warranty card or contact the manufacturer for more info in this regard.
  • When turning to expose the cutter area, make sure that the carburetor is on the top side.

Final Remarks:

The health of lawnmower blades decides the quality of your mowed lawn directly. When you use your mower for some time, the blades become dull and blunt. When this happens, the grass is not cut cleanly, so it turns dark quicker. This gives an ugly look to your lawn. Though it is possible to sharpen the blades, some defects can’t be removed with a sharpening. Such defects include dents, chips, and twists. It is good to examine the blades and regularly sharpen them when needed. When the blades’ condition becomes that they can’t be sharpened, replace them with a new set. The replacement procedure is not complicated at all. You can follow the guidelines presented in this article to replace your old lawnmower blades.