Unbalanced lawn mower blades can cause big problems.

You might not think an unbalanced lawn mower blade could cause damage to your mower but as you will see from this topic on the Gopher Lawn Care Business Forum, anything out of balance that is spinning over a thousand times a minute can cause big problems. In this discussion we see how an unbalanced mower blade can not only cause an uneven cut but also shake components apart.

One lawn care business owner wrote “this week the pulley over the center lawn mower blade of my ztr pulled 2 bolts off the deck and was tilted back. It left me with about 2 hours of push mowing last Saturday. I wasn’t sure of the exact threads, so I installed 2 bolts that just fit through the holes with washers and nuts on the end. They snapped off in about 4 seconds.

As I tried to undo one of the other 2 bolts to take one to the hardware store to buy the correct thread, it snapped off. There are 4 bolts holding the center pulley/blade to the housing. Now 2 are missing and 2 are broke off. Sooo, I drilled out the holes slightly bigger, re-threaded them, and installed new tightly fitting bolts. More importantly, I got to the root of the problem, an unbalanced mower blade.

I grinded off the back side of the heavier part of the blade until it seemed balanced (stayed still when the deck was held vertically). So far so good. This probably sounds dumb but I didn’t realize an unbalanced blade would snap off bolts in 4 seconds. Lesson learned. Do you guys have a way to keep blades balanced or check them, or can you just know somethings wrong by the vibrations? Instead of grinding one side, do they make strong enough little magnets or weights to add to the light side?”

A second lawn care business owner said “usually I just take the blade off and balance it on a piece of wood or a blade balancer. If one side is heavier, I grind it a little more… Eventually it becomes balanced with a little time.

If you feel an awkward vibration when you are mowing, your blades are most likely unbalanced. I don’t know about magnets working too well. I don’t think I would even attempt something like that when it is so easy to grind down the heavier side of the blade.”

A third added “Stick a bolt or screw horizontally in a vise. Put the blade hole over that.
Which ever end is down gets the weight removed. Some mowers have a star or spline center hole. There is a cheap blade balance tool that is available and looks like a cone so you can set the blade on it and see easily if the blade is balanced.

Lawn Mower Blade Balance Tool

Lawn Mower Blade Balance Tool

Once your blades are balanced right, make sure you sharpen equal amounts from both ends. And NEVER, let me repeat, NEVER, grind from the back side of the blade. Always grind more off the cutting edge of the blade. Grind the blade as if you were sharpening a dull blade. This is the only acceptable way to sharpen the blade.

The reason for this is that if you grind off the back of the blade, you will affect the effectiveness of the grass discharge because the upturned part of the blade is what lifts the grass to give you a cleaner cut, discharges the cut grass, and helps keep the underside of your deck cleaner by discharging he grass out the side or bagging it. Needless to say, if you grind too much off the back you would most likely never be able to bag with those blades again. Also do not grind off the ends since the length of the blade is what keeps you from having skips in the grass where you just mowed.

Lawn mower blades can get out of balance to the point that it will literally shake your entire mower. This not only affects your deck by vibrating bolts loose, but also the rest of the mower.”

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