Do you bother to sharpen your lawn mower blade? Why?

Hmmm, I sharpen it myself when blade becaomes dull. You can tell the difference between good blade and dull blade. Dull blade does a poor job of cutting. It just beat up the grass blades. Compare between two grass tops. One cut with a good mower blade and one with dull blade.

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Couple of years ago used to cost $3 to $4 around here. Biggest job is often getting the blade off!

Easy enough to do on a bench grinder or in a vise with a big 'bastard'' file.

But make sure the blade is balanced afterwards.

Recently modifying and rebuilding a mower was able to shorten a blade by grinding off the ends and then sharpen it.

I think I'll learn how to sharpen my blade and see if it makes a difference.

Interestingly, this video says the blade is the flywheel ... and that the "flywheel" at the top is really just a cooling fan.

This video is from a very experienced lawnmower mechanic who advises against removing the blade to sharpen it.

Why do all the manuals recommend removing the blade to sharpen it while this admittedly very experienced mechanic says not to bother?

I can't watch the video now but I presume he counts the number of strokes he uses and has enogh practice to make sure the strokes are with the same amount of pressure and the same distance from the center on each end. That is 2 strokkes at 8 inhces, 2 strokes at 7.5 inches,

AFAIK, so it can be balanced afterwards.

Strange. The thing at the top does have a fan, but which has the greater angular momemum? Or the bigger integral of distance from center x mass for the whole diameter of the blade versus "flywheel".

I don't know. The length of the blade is greater than the diameter at the top, but the thing at the top is a whole circle and pretty thick, not just a thin blade 2 inches wide or so.

Whichever's is greater could be considered the flywheel, I guess, because it does more to keep the engine spinning smoothly, even though it's a one-cylinder engine.

The blade on horizontal small engine lawnmowers acts as the flywheel. It provides the inertia to keep the motor turning. It's almost impossible to hand start the engine without the blade or if the blade is loose and spins on the crankshaft. The small engines that don't use the blade for the flywheel have a heavier flywheel. The aluminum key is actually there only to align the flywheel on the shaft, the crankshaft is tapered and the flywheel is held tight by the nut or starter mechanism. The blade, if it's not bent and there is enough left to sharpen, then sharpen and balance it. Don't worry about getting all the nicks out of it. I usually use the body grinder when I sharpen one, using a file can take a long time, always balance the blade. Ask the local mower shop what they charge to sharpen a blade, and they will have replacement blades and contrary to what the manual says you can usually get replacement at many box stores that will work just fine. Make sure the replacement is EXACTLY the same as the old one. There are 6 point star holes and 4 point and square ones and diamond shaped ones and some have three holes, mulching, non mulching and of course the proper length. I'd stay away from the blades that use inserts to correct for the main bolt hole size. The last blade I bought was made in France and needed balancing even though it was brand new. The last trimmer string feed bump head I bought was made in Italy and is a flimsy POS. Have fun, tell your neighbors, friends, and co-workers you will take their old mowers and weed trimmers, you should have a collection by the end of summer to fix. Surprising how many of them just need a carb cleaning, spark plug, starter rope, cable etc. and they are good for another couple years. Some aren't worth fixing but many have a lot of good hours left in them. Oh yeah, speaking of cables, the one that pulls back the safety brake and kills the engine when you release it, make sure it's in good shape and pulls the safety brake completely back. It will cause a drag on the engine if it doesn't and makes it hard to pull start. It's a good hobby fixing old mowers and weed trimmers, keeps you in shape pulling the starter ropes on those old dogs.

He doesn't use a file. He uses a hand-operated grinding wheel (DeWalt type). It is interesting to note how he does it w/o removing the blade.

Nope-- I watched it. he gets to sharpening at about the 4 minute mark. He uses an angle grinder.

For a $50 mower I might do the same. Otherwise I either take it off so I can balance it, [I look at that struggle as a practice run for blade replacement] or I do the above with a file.

Or more likely I just wait until I think it needs it and replace the blade-- leaving the old one on the bench to be sharpened at some future date-- hoping the mower has died by then and the new one takes a different blade.

It is also a bit safer. The mechanic never mentioned that you should always remove the sparkplug when messing with the blade. Compression can bump a blade enough to do damage.

Sometimes experience doesn't equal wisdom. . . nor does it necessarily mean you are a good teacher.

Jim

That's why you check to be sure your blade is tight. I spent many hours on a mower learning *that* lesson. Finally broke down and asked my neighbor to look at it.

First thing he looked at was the blade- 10 seconds and a big wrench later I was good to go.

Jim

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Dull blades rip the grass and will burn the top in hot summer, it takes about 15 minutes to use a file yourself.

Yes (3 blades, riding mower), sometimes.

Cuts better. Briefly.

I don't do it as a matter of course, just if I happen to have to drop the mowing deck for something else. And if you think blades are indestructible, you should see mine after a season or two...not much left.

Yes, mostly tradition. A sharp blade cuts the grass easier, a dull blade tends to beat the grass rather than slice it. I do my own sharpening with a bench grinder.

Shears aparently lives on the residual income of off-spec parts. Their mowers won't accept Briggs or Tecumseh parts in many cases, so you end up going to Shears and buy their parts.

Try starting the mower with no blade. Gently -- the experience is a real arm yanking moment. The blade is essential, in addition to the flywheel.

Can't balance blade while on mower. I sense the old guy is tired, and doesn't want to be bothered.

I sharpen mine occasionally with a hand grinder. I never bother with the balancing.

I sharpen mine every spring. Nothing cuts like a sharp blade. (that's why) Dull blades just tear the grass. If you keep them sharp it doesn't take long on the grinder. If you wait until it's blunt, it may take a while to get the cutting angle planed and edge sharp again. Like any other maintenance, let it slide and it's more work to get back into shape. It also pays to clean up your lawn and remove the rocks. If you never hit stuff it stays fairly sharp. I like a knife edge.

Hi Jim, Thanks for watching the video. I should have mentioned it was about 4 minutes in that he sharpened the blade. I appreciate your time and effort.

I wouldn't remove the sparkplug; but I would pull the wire off the spark plug (and yes, the mechanic didn't mention that).

He ground the upper part of the blade and then the lower part briefly with the angle grinder but I agree he didn't balance it afterward.

The owners manual I have says to hammer a nail protruding out of a wall stud and hang the blade horizontally on that nail from the center hole to balance.

So, even if I sharpened the blade on the mower, I'd still have to remove it to check the balance. I guess he has so much experience that all his checks showed his blades were still balanced after he sharpened them.

I've never sharpened a blade before.

May I ask:

If I sharpened the blade, and if it was slightly unbalanced, would I know it was unbalanced when I started up the lawn mower?

If yes, then there's less reason to balance ahead of time; if not, then why bother balancing?