This video walks you through the whole process step by step, including blade and blade boss inspection, bolt removal, fitting new blade, and torque blade bolt to specification.
An old worn-out blade will cause a ton of problems, including:
- Engine vibration, which can lead to a list of more serious issues.
- Lawn damage, old blades tear the grass instead of cutting clean, torn grass leads to excessive moisture loss and yellowing of the lawn.
- Clogged grass chute, the worn blade wings no longer creates enough force to lift the grass or to move it to the bag. This results is persistent and annoying clogging and clumping on the lawn.
Replacing the blade will solve these issues. But the process is important, especially tightening the blade. Too loose is bad, yes! But too tight is a problem also.
The blade is designed to slip on the blade Boss (blade mount), just a little in the event of a blade strike (curb, stump, dog toy, etc.). If the blade bolt is buttoned up too tightly, it can’t slip and the energy is therefore transferred into the crankshaft, which may cause it to bend.
That’s bad news for a motor, sure it can be fixed, but it means engine strip down and fitting a new crankshaft. The labor and parts can add up to more than the price of a new motor.
Anyhow, this video covers the tightening (torque) of the blade bolt, but you will need to check your mower blade bolt torque specifications, they are model specific. You’ll find a video here on torque wrench use and cars and a link below to the torque wrench I use.
Before working on your mower be sure to remove the plug wire to prevent accidental starting, see “Repair Safety Video”.
You’ll find useful resources on this page, tips, links to tools, parts, and supplies required to complete your repair.
Tools & Parts
To nail this procedure you may need the following tools, parts, and supplies.
This is the first tool on the list for good reason, WD solves a ton of problems. I won’t work without it, because I can’t. Picture links to Amazon.com.
Ratchet Tool Set
Before we can do anything, we’ll need tools. I’ve selected this set as I own some Craftsman tools and while I have worn some out, they did do a lot of work. So I expect this set will last the occasional user quite a long time. This set carries both metric and standard sockets and that’s important because some mowers will have both types of fastener sizes. Set includes spark plug sockets. Picture links to Amazon.com.
Gas Line Clamp
Some small engines will have a gas tap, which is really handy when removing the carburetor, stops gas flowing all over the shop. However most engines won’t have one, these useful clamps simply squeeze the fuel line and prevent a spill while you perform surgery. Picture links to Amazon.com.
I love DeWalt, they make quality tools. This heavy-duty but lightweight 1/2 inch impact wrench makes short work of stubborn bolts like flywheel nuts and rusty blade fasteners. Up to 700 ft-lbs of torque on tap, I keep one in the trunk of our family car, which makes a flat almost enjoyable. Picture links to Amazon.com.
I use a DeWalt screw gun (also a drill) in the workshop to speed up the process of removing engine covers, carburetor bolts, Armature bolts, etc. It’s a brushless motor and as tough as nails, I drove over it a few times – still works great! Batteries are interchangeable and so if you have a DeWalt product already you won’t need the battery. Picture links to Amazon.com.
Teng 1/2 Torque wrench, a fantastic tool I use it every day, and mine is still going strong. A torque wrench is advised for tightening components such as flywheel nuts and blades. The torque spec of these components is very important. Picture links to Amazon.com. If you’re buying a torque wrench, check out my review of Teng torque wrench, it’s the model I use.
Blade Sharpening Tool
Handy blade sharpening kit that fits a cordless drill, includes blade balance tool. Picture links to Amazon.com.
Blade Holding Tool
The very useful blade holding tool is used to hold the blade steady while the blade bolt is loosened and tightened. Picture links to Amazon.com.
Wire Brush Kit
Stainless for heavy-duty and brass for and brass wire brush kit for heavy-duty and finer applications like electrical connections and softer metals. Picture links to Amazon.com.
Wire wheel and drill make life easy and the job almost enjoyable! Picture links to Amazon.com.
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- About the Author
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John Cunningham is an Automotive Technician and writer at Lawnmowerfixed.com.
He’s been a mechanic for over twenty-five years and shares his know-how and hands-on experience in our DIY repair guides.
Johns’s fluff-free How-to guides help homeowners fix lawnmowers, tractor mowers, chainsaws, leaf blowers, power washers, generators, snow blowers, and more.