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Follow all safety instructions provided in your equipment operator’s manual before diagnosing, repairing, or operating. Consult a professional if you don’t have the skills, or knowledge or are not in the condition to perform the repair safely.
How Often Should You Change Your Mower Blades?
Lawn mower blades should be changed once a year. Blades that are exposed to more dirt and gravel should be changed more frequently.
Replace your mower blades annually when performing the routine annual service on your mower.
If the blades you are replacing aren’t damaged and excessively worn, sharpen the blades and keep them on hand just in case you damage your new blades while mowing and need an extra set to finish the mowing job.
How Often Should You Sharpen Your Mower Blades?
Your mower blades should be sharpened after every 25 hours of use. For the average homeowner, you will be sharpening your mower blades twice a year.
Again, when operating in sandy and gravel conditions, you will have to sharpen your blades more often in order to maintain a good cut.
Do New Blades Need to Be Sharpened?
New mower blades do not need to be sharpened before you install them on your mower.
This is because the blade manufacturer sharpens them during the manufacturing process and then coats the blade in paint. The paint will wear off the blade edge when you begin cutting with it.
Check Your Mower Blade for Excessive Wear and Damage
A dull blade or one that has excessive wear or damage can compromise the cut quality given by the mower. If you are experiencing a bad or uneven cut with your lawn mower, it’s a good idea to check the condition of your mower blades.
Blade Sail Wearing
The sail of the blade is the high side of the blade. Over time, dirt sucked under the deck can wear the sail so it becomes thin.
When the sail is not in good condition, it is unable to move the air required to form a suction in the deck to stand the grass tall while the blade gives it a precise cut.
Replace a mower blade where the sail on the blade is thinner than the center of the mower blade.
Chips & Gouges
When your mower blade has nicks in the blade edge, the cut quality if compromised. Small chips in the blade edge will, most likely, be able to be smoothed out by sharpening the blade edge. Replace the mower blade where larger nicks and gouges exist.
Bent Blade
A bent mower blade will negatively affect the way your mower cuts. A blade can bend when you hit a solid object like a tree root or a rock.
It’s best to match your old blade up to a new blade to confirm whether or not you have a bent mower blade. If you don’t have a new blade for comparison, remove your blade and bring it to your local dealer to have it looked at.
Never attempt to straighten and reuse a bent blade. This compromises the blade’s structure and can cause it to crack.
Cracked Blade
A cracked mower blade must be replaced right away. A cracked blade spinning at high speeds under your mower deck is prone to break off and fly out of the mower. This can put people, pets, and structures in the area at risk of injury or damage.
Items That Can Prematurely Wear & Damage Your Mower Blade
It’s good practice to walk your lawn before you mow it to remove any obstructions or items that could be damaged by your mower or could cause damage to your mower. These can be toys, sticks, and rocks.
Sand and debris can cause your blades to wear prematurely, but there really isn’t much you can do about this other than grow a thicker blanket of grass to cover your lawn to reduce the amount of dirt being sucked into the mower deck.
If you choose to use lawn chemicals to help with the growth of your lawn, some may be corrosive to your mower blades and deck. I recommend regularly cleaning and removing your blades.
The corrosion can cause your blades to fuse to your deck components making them nearly impossible to remove without causing damage. Frequently removing and installing the blades will reduce the likelihood you develop this problem.
How to Remove & Install Your Mower Blades
Gather Tools
- Socket wrench
- Work gloves
- Safety Glasses
- Torque Wrench
- Block of Wood
Remove Your Mower Blade
- Take safety precautions: Again, make sure your spark plug boot is disconnected, and remove the key if your mower has one. Wear a good pair of gloves before working with your mower blades.
- Prepare the mower & lay it on its side: Turn the fuel valve to the off position to minimize gas leaking when laying your mower on its side. Tip the mower so the air filter is on the high side of the mower.
- Remove the blade bolts: Lodge a block of wood between the blade and the deck housing to prevent the blades from turning when removing the bolts and washers with a socket wrench.
- Remove your mower blades
Install Your Mower Blade
- Clean the area under your deck where your blade mounts before installing the replacement blades. If you are reusing your old blades after they have been sharpened, make sure they are balanced. Refer to the section below on a balanced blade.
- Install the upper and lower blades and tighten them with the bolts and washers. Make sure the concave side of the washer is facing the blade.
- Tighten the bolts using a torque wrench to tighten the bolts to the manufacturer’s specification as shown in your owner’s manual. Make sure you torque them correctly to avoid injury so your blade doesn’t come off the mower. Use a block of wood to help keep the blade from rotating as you tighten the bolt.
How to Sharpen Your Mower Blade DIY
You can save time and money by sharpening your own mower blades. The amount of money you can save depends on the method you choose for sharpening your blade.
Sometimes it’s just not worth it to do it yourself. You’ll have to determine what’s best for you. Here are some tips if you choose to sharpen your own mower blade.
Gather the tools you will need
- 10″ flat metal file, drill-powered blade sharpener, or disc grinder
- A vice to hold the blade in place
- Blade balancer or nail on the wall
- Rags
- Wire Brush
- Safety glasses
- Work gloves
Clean Mower Blades
Put on your work gloves and safety glasses. Use a rag to clean the dirt off your mower blades. A wire brush can be used for stubborn areas of buildup.
Secure Your Mower Blade
Securely place your blade in a vice to keep it from shifting during sharpening. After sharpening one side, you will flip the blade and secure it in the vice while you sharpen the other side.
File or Grind Blade Edge to Sharpen
Sharpen with a metal file
- Using a file, push the file at an angle in one direction along the blade.
- Do not use a sawing motion when filing.
- Once all the rough spots and uneven edges are removed, flip the blade over, secure in the vice, and sharpen the other side.
Sharpen with a drill-powered blade sharpener.
- Power the drill with the blade sharpener attached.
- Place the flat guide of the sharpener along the flat portion of the blade with the cutting edge slot into the bevel.
- Move the sharpener up and down the length of the blade edge.
- Once one side is sharpened without any rough spots or nicks, flip the blade over, secure in the vice, and sharpen using the same procedure.
Sharpen with an angle grinder or bench grinder
- Hold the angle grinder perpendicular to the edge of the blade. Run the grinder along the length of the blade to level out any rough spots or nicks. Keep the grinder moving so it removes a little metal at a time and produces an even result.
- Once one side is sharpened without any rough spots or nicks, flop the blade over, secure in the vice, and sharpen using the same procedure.
How to Balance Your Mower Blade
It is necessary to balance your mower blade before reinstalling it on the mower. Failing to do so can cause vibration and damage to your crankshaft.
A balanced blade is one that has equal weight on each side of the blade. Use a blade balancer to check the balance of your blade.
If you don’t have a blade balancer, you can place a nail in the wall with the nail head about 3/4″ to 1″ away from the wall. Place the center of the blade on the nail.
You want the blade to sit level while balancing on the nail head. If it doesn’t, shave a little more metal off the side of the blade that is hanging lower until it sits even with the other side.
When Should You Seek a Professional Sharpening Service for Your Mower Blade?
You should seek a professional when you aren’t quite comfortable with your blade sharpening or balancing skills. If your blades are not correctly balanced or still worn, you could cause additional damage to your crankshaft or engine.
Personally, even though I have the tools to sharpen my own mower blades, choose to have my local lawn mower dealer sharpen my blades. They just put a nicer cleaner edge on the blade than I can achieve.
You may choose to have a professional sharpen your blades because:
- It is a safer option to sharpen the blade yourself
- Sharpening a blade is often less expensive than purchasing a blade
- A professional can grind down mower blades to get rid of large nicks and gouges in the steel
- The blade is properly balanced. This will reduce vibration and damage to your mower.