A job that a lot of people neglect throughout the year is keeping the blades on the mower nice and sharp. By keeping the mower blades sharp it makes for a cleaner cut, and causes less stress to the grass allowing it to recover quickly, imagine the difference between a nice clean surgical cut versus a jagged cut from a steak knife, which would heal faster and which would have more chance of infection?
If you have dull blades they will rip and pull at the grass and in extreme cases will leave little strings attached to the ends of grass blades, where its edges are frayed and damaged, that’s how you know you’re overdue for sharpening or replacing your blades!
It’s a relatively simple task, but it might take a few attempts to fully master the technique.
Below is a basic 6-step guide for sharpening your mower blades:
1. Remove the spark plug
Before doing any repairs involving a mowers blade it’s important to make sure you can’t accidentally start the mower. So remove the spark plug and give it a quick clean at the same time. It is unlikely you could start the mower but using a ratchet gun could accidentally start the mower. Better to be safe.
2. Tip it backwards or on its side
The ideal location to change the blade is with the mower the way it sits normally, but we do all have a hoist in our garage. The next best is to tip backwards at the handle lifting up the front of the mower. If you have no way to properly secure the mower in this fashion it is safer to put the mower on its side.
3. Remove the blade
All mower blades are removed differently so this should be considered general advice and may not apply to your model of mower.
Blades usually come with 4 smaller blades attached to a plate or 1 blade that runs through the middle from side to side. They are both removed the same way with a single bolt through the middle, this is often a reverse thread (undoes the other way) to prevent unspooling when mowing.
Lubricant may be required if its been a while since you last removed the blades.
Tip: it can be confusing to work out which way the blade lies so before you remove the blade, mark it with spray paint so you can reinstall it correctly. If you don’t put it in the right way the blade won’t cut!
Check the blade(s) for any rust or excessive wears. If there is any bent areas or signs of deterioration, it’s best to replace the blades so skip ahead to step 6. If the blade is in good shape then we can proceed to sharpening.
Tip: It’s always a good idea to keep a second set of blades on hand at all times, that way you can rotate between the two and don’t forget to use your old one for renovations.
5. Sharpen the blade
We recommend sharpening with a hand file for maximum control and safety of your handiwork. Angle grinders are also a great way to sharpen you blades, work well and are much faster, but if you’re not experienced you risk your own safety as well as overheating the metal and damaging the blade. Remember if the blade is badly damaged replace as you do not want parts of this to come spinning from your mower.
6. Reinstall the blade
Reinstall the blade the same way it was mounted before and tighten. A loose blade will throw off the engine timing and make your mower more difficult to start, so make sure it’s tight enough!
Blades should be checked on a regular basis and immediately if you have accidentally run over a large object in the lawn.
Unsharp mower blades are the most common reason for a mowers poor performance, but not the only one. The main other issue is poor blade tip speed and there can be several causes for this which include:
Engine trouble- If you have failed to service your mower properly than your engine may be running at a reduced level of performance, slowing down the blades
Wet or thick grass- If you try to mow to low or your longish grass is wet this means the mower is working harder to cut the grass, this results again in the blades slowing and poor pickup of clippings as well as the cutting of grass.
Low throttle- A lawn mower is a relatively simple machine and the throttle cable is generally held in with one bolt, as the mower vibrates around your lawn sometimes this loosens over time allow the cable to release slightly. This results in lower engine revs and you guessed it lower blade speed. It is best to get a mechanic to adjust this as increasing the engine speed to much can result in to much strain on the engine and a very short life span.
There is another reason for poor cut quality but it isn’t super common because people don’t usually run across their lawn…
It’s important to match your ground speed to your mowers speed, the slower you go the more revolutions per minute your blades will have and the more likely it is to get a clean cut.