Noticing uneven cuts or ragged grass tips? It might be time to check your lawn mower blade. Whether you're using a traditional mower or a robotic one, keeping the blade sharp and in good shape is key to a healthy, great-looking lawn. In this guide, we’ll help you figure out when it’s time for a new blade, how to change a lawn mower blade in 5 easy steps, and share expert tips to help your blade last longer—so your mower keeps running smoothly and your lawn stays well-groomed.
When to Replace Mower Blades?
Sharp blades are your first line of defense for a healthy, even lawn, so keep an eye on your mower blade’s condition helps avoid lawn damage and mower strain. Here are clear signs it's time for a change:
Uneven or Ragged Grass Cuts
If your lawn looks more torn than neat after mowing, that’s a common sign that your blades are dull. Blunt blades shred grass instead of slicing it cleanly, causing ragged edges that stress the plants and make them vulnerable to disease. Even a well-timed mow can leave your lawn looking sloppy if the cut is uneven. Don’t wait for symptoms like patchy grass or brown tips, once blades “tear rather than cut it clearly,” it’s time to act.
Increased Noise or Vibration
Have you noticed your mower suddenly humming louder or shaking more than usual? This could mean your blade is bent or unbalanced. Uneven weight causes the mower to vibrate and puts extra strain on the spindle and engine. Over time, that vibration may lead to mechanical wear or worse. It’s suggested to replace or balance blades at the first sign of rattling.
Blades Appear Worn, Bent, or Rusted
Physical damage like bends, chips, rust, or cracks is a clear sign that it's time to replace your mower blade. These issues shouldn’t be ignored, as even small bends can disrupt airflow beneath the deck, which in turn reduces cutting efficiency and forces your mower to consume more fuel or battery. Rust, in particular, is especially problematic because it weakens the blade structure, making it much more likely to break mid-mow. To avoid these risks, it's a good idea to inspect your blades visually at the end of each season, or immediately if you notice any signs of damage. If something looks off, replace the blade right away.
Battery Drains Faster
For battery-powered robotic mowers, a dull or damaged blade raises resistance and makes the motor work harder, resulting in quicker battery drain. If your smart mower seems to need more charging between runs, don’t just blame the battery, it could be time for a blade check or swap.
Blade Replacement Schedule
How often to replace mower blades? For traditional lawn mowers, it's recommended to sharpen the blades every 20–25 hours of mowing and replace them every few years, or sooner if they become damaged. However, for robotic lawn mowers, it's generally better to replace the blades and screws every 1-2 months rather than sharpening them. Why? The blades on robotic mowers are typically attached with screws, and sharpening them can lead to an imbalance, which negatively impacts mowing performance. In other words, replacing the blades regularly ensures your mower operates efficiently and delivers optimal cutting quality.
Now that you know the common signs that it's time to replace your mower blades, how do you change the blade on a lawn mower?
How to Change a Lawn Mower Blade in 5 Simple Steps
Improper blade replacement can lead to injury or a poor fit. Follow this step-by-step guide to replace a lawn mower blade safely and correctly.
Get the Right Tools
Before diving in, make sure you have the right tools on hand. Start with protective gloves, a screwdriver (or socket wrench if it’s a large one like a walk-behind lawn mower) that fits your blade bolt, a water hose for cleaning, or a block of wood or blade holder to prevent spinning (if needed). Usually it’s suggested to use the manufacturer's OEM tools or kits designed for robotic mower blade changes.
Turn Off the Mower
Safety first: disconnect the power source. For gas models, disconnect the spark plug. For electric or robotic mowers, remove the battery or unplug. That ensures the blade can’t accidentally turn mid-service. A small precaution like this can prevent severe injury or damage.
Place the Mower Properly
You’ll want stable and easy access to the blade. For gas mowers, tilt the mower gently with the air filter and fuel tank facing up to prevent leaks. If you're working with a robot lawn mower, place it upside down on a soft, clean surface to avoid scratching the shell and keep it from wobbling while you work.
Remove the Screws and Blades
Now it’s time to remove the blades. For gas mowers, use a wrench to loosen the bolt while holding the blade steady, then carefully remove the blade. Be sure to keep the bolt and washer—you’ll need them when installing the new blade. For robotic lawn mowers, you’ll likely need a screwdriver to loosen the screws. Avoid using an electric screwdriver, as it can slip and cause injury or damage the blade disc. Once the screws are out, remove the blade and set everything aside for the next step.
Fasten the New Screws and Blades
For gas mowers, align the new blade and secure it with the bolt and washer, tightening it to the torque specification in your manual. Reattach any protective covers or parts you removed. Once everything is secure, reconnect the power, whether that’s plugging in the battery or reconnecting the spark plug, and you’re good to go.
For robotic lawn mowers, it’s a good idea to clean the mower before reinstalling the blades. Once the new blades and screws are in place, make sure each blade can spin freely without obstruction. A quick check now helps ensure safe and smooth operation later.
Tips to Extend the Lifespan of Your Lawn Mower Blades
Once you're in the groove of swapping blades, these expert tips will help your mower run better and keep your blades performing at their best for longer.
Mow When the Grass is Dry
Avoid mowing wet grass. Why? Wet grass tends to stick to the blades and the underside of the mower, which can reduce cutting performance and make cleanup a hassle. It also dulls the blades more quickly and leads to clumping inside the deck. It’s best to wait until the morning dew has evaporated, usually a few hours after sunrise, or mow later in the day when the grass is dry.
Avoid Rocks, Sticks, and Debris
Before you start mowing, take a few minutes to scan your lawn and remove any visible debris. Even small stones or twigs can quickly dull or chip your blades, leading to poor cutting performance. If you can’t clear everything, raising the mower deck height can help reduce the risk of impact. This small bit of prep goes a long way—it protects your blades, prevents potential damage, and saves you time and repair costs later on.
Clean and Inspect the Blades Regularly
After each mowing session, it’s a good idea to unscrew the blade and wipe off any grass, dirt, or rust that may have built up. Once it’s clean, take a moment to check for any nicks, bends, or other signs of wear. Spotting these issues early allows you to sharpen or adjust the blade before they lead to poor performance or further damage. If that feels like too much after every mow, even a quick weekly check can go a long way in keeping your blades healthy and your lawn mower running efficiently.
Use High-Quality or OEM Blades
Go with OEM or high-quality aftermarket blades, as they’re made to fit precisely, stay balanced, and typically last longer. For example, the Navimow i Series robotic lawn mower offers compatible replacement blades designed specifically for the system. These blades hold their edge longer than generic alternatives, which means fewer replacements and more consistent performance over time. You can also find official blade replacement guides on the website, which help you avoid safety risks and damage caused by incorrect installation. With better durability, easier maintenance, and improved mowing results, investing in quality blades is well worth it.
Knowing how to change a lawn mower blade is essential for keeping your mower running smoothly and your lawn looking its best. Whether you're using a gas mower or a robotic one, replacing worn blades at the right time and following a safe, step-by-step process makes all the difference. Pair that with a few simple maintenance habits, like cleaning, inspecting, and choosing high-quality blades, and you'll get better performance with less hassle. Ready to tackle your next blade change? With the right tools and tips, you're more than equipped to do it right.
FAQ
How often to replace mower blades?
If you have a robotic lawn mower, it’s better to replace the blades and screws every 1-2 months rather than sharpening it. If you have a gas mower, you should sharpen your lawn mower blade every 20–25 hours of use, or at least twice during the mowing season. If you notice uneven cuts, tearing grass, or visible damage like chips or rust, it's best to replace the blade altogether.
Can I use an electric screwdriver to remove the blades?
It’s best to avoid using electric screwdrivers because they may not provide the right torque or could apply it too quickly. They can also slip, which might cause injury or damage the blade disc.
Why are the blades still loose after I've tightened both the blades and screws?
For certain lawn mowers like the Navimow i Series, you might notice the blades still feel loose even after tightening the blades and screws. This is completely normal because the blades are designed to spin freely when attached to the blade disc. During mowing, the blade disc spins and creates centrifugal force, which pushes the blades outward. This outward movement is what allows the blades to cut grass effectively and efficiently.
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