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Do You Need To Sharpen New Mower Blades (Beginners Guide To Blades)

By: Author John Cunningham. Published: 2019/11/14 at 3:59 pm

Aaah…I love the smell of fresh-cut grass, but joy can quickly turn to frustration when using a dull lawnmower blade. Grass trailings, uncut grass, clogged mower, and the list goes on…

So, do you need to sharpen a new mower blade? New lawnmower blades come readily sharpened; there’s no need to sharpen a new lawnmower blade.

In this post, we’ll answer beginner questions about lawnmower blades. And also what you must not do when changing your lawnmower blade.

In the future, if you need video help on inspecting, removing, sharpening, balancing, refitting, and torquing your mower blade, check out “Mower blade sharpening video.”

Do I need to sharpen lawn mower blades?

Lawnmower blades need to be sharpened regularly. A dull blade will pull and tear on your grass blades, causing jagged tips. The dull blade stresses the grass, and the damaged grass tips turn yellow. A sharp blade will cut cleanly, which is healthier for the lawn and easier on you and your mower engine.

How often should mower blades be sharpened?

At the very least, your mower blade needs to be sharpened at the start of every new season and, more often, if your yard is stony or large. Setting your mower cutting deck to the lowest level will cause the blade to impact objects more often and will obviously need more regular sharpening.

Sharpen once per season, at least.

When should I replace my mower blade?

A mower blade should be replaced about every third to the fourth season. But it really does depend on its condition; a mower blade that cuts a small mature yard will last longer. New yards usually have rocks, stones, and debris that impact the blade, causing it to become dull and wear out quickly.

Blade wear – Check out the wear on this blade; this mower was having all kinds of cutting and bagging problems. A New blade solved all.

How do I know if my mower blade needs to be sharpened?

A mower blade doesn’t need to be knife sharp, but the leading edge of the blade does need to be beveled and the face free from gouges. Examine your blade by turning your mower over on its side but always with the carburetor side facing the sky (prevents gas spill).

Wearing a glove, run your finger along the beveled blade. Are there large indentations or gouges? If the answer is yes, then your blade needs to be sharpened.

Can you sharpen a lawn mower blade without removing it?

You can sharpen a mower blade without removing it, so long as it is not badly damaged or worn. The best practice is to remove the blade from the mower, sharpen and then balance it.

Sharpening the blade on the mower runs the risk of unbalancing the blade, which will cause the whole mower to vibrate.

Check out “Blade maintenance tools” here; they make the sharpening process a ton easier, or check out the Amazon link below.

Amazon Lawnmower Blade Sharpening Tools

Tools -This method is only suitable for relatively new blades. You’ll need a big flat metal file, move the file at 45 degrees with the bevel, and to finish, run the file across the rear to clean the burrs. If your blade is heavily damaged or badly worn, this method isn’t suitable.

The “Mower blade sharpening video” covers the whole process, both on and off the mower.

Should I sharpen or replace my lawn mower blade?

If your mower blade is more than four years old and has seen average use, then go ahead and replace the blade. Good quality blades aren’t expensive, but note you will need a torque wrench to tighten the blade bolt to specifications.

Tightening a mower blade without using a torque wrench runs the risk of the blade coming loose or destroying the engine. I wrote a post about my torque wrench here: “Best torque wrench for mower blades.”

Sharpen or replace

Unless your blade is in good condition, I’d spring for a new one. They’re not expensive, but you’ll need to buy or borrow a torque wrench.

How tight should mower blades be?

It’s important to tighten your blade to the correct specification. A mower blade may not be as tight as you might expect.

A blade fits on a blade boss (metal block), which is then fitted to the end of the engine’s crankshaft. A blade is designed to slip on the blade boss if the mower blade hits a solid object.

Over-tightening the blade will prevent the blade from slipping on the boss and will instead bend the crankshaft and destroy the engine.

Check out the video on blade fitting; it covers torquing the blade to specification. You might find the video on using a torque wrench.

Can you sharpen a Mulching blade?

You can sharpen a mulching blade; it is sharpened in the same way as a collecting blade; the best results are achieved by removing it before sharpening and balancing.

Which way do mower blades tighten?

A single-blade lawn mower blade bolt will be a right-hand thread. Viewing the mower on its side (carburetor side up). To tighten the bolt – turn clockwise. To loosen the bolt – turn anticlockwise. I wrote a post on a similar subject “How to remove stuck blade bolt”

Which side of the lawn mower blade is up?

All mower blades will have a lifted trailing edge. The lifted edge points upwards to the underside of the lower body.

This side up

Do lawn mower blades need to be timed?

A single-bladed mower will not need to be timed. Twin-blade walk-behind mowers like a Toro or some lawn tractors will need blade timing. The purpose of the timed blades is so the blades can overlap.

Overlapping blades help prevent uncut grass between the blades. If your blades can touch each other, then yes, it’s likely you have a timed deck, and the blades will need to be timed. I wrote a post about timing your mower blades here “Replacing timed mower belt”.

Timed Blades

What causes a lawn mower to cut unevenly?

There may be several reasons why your mower is cutting unevenly; here are some of the more common reasons:

  • Deck wheels are set to different heights (Walk behind mower)
  • A bent/worn blade
  • Uneven tire pressures (tractor mower)
  • Deck needs to be leveled (tractor mower)

Should the front of a push mower be lower than the back?

A lawnmower deck should be level, front to back, and side to side. All mowers will have a height adjuster; some will have a single lever, and others will have a height adjuster at each wheel. Level the deck by adjusting the wheel heights.

Level – Adjust all-wheel heights until the deck is level.

What does a high-lift mower blade do?

A High-lift blade has a trailing edge that lifts sharply upwards. This causes a powerful vacuum effect on the grass blades, lifting them upright before cutting them. The high lift blade is specially designed to collect grass, and it does so really well.

An engine will need to be sufficiently powerful to drive a high lift blade; not all mower engines are. Check with your dealer before fitting a high-lift blade.

Mower Troubleshooting