Mower wobbles after blade hits rock.

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My Black&Decker electric mower was loan to friend. He ran the mower over several boulders several times, chipping a couple pearl size sections off the blade. Possibly, this is causing the mover to vibrate to the point of causing a shoulder sore.
I remove the blade, then clamp it to a vise grip. I have an angle grinder that I will use to fix the balancing problem. The problem is, I've never done this before. What is a practical way to balance a mower blade?
Thanks
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Sears and other places that sell mowers will sell a small cone shaped device on which you position the mower blade before and after grinding to determine if it's balanced, probably not more than $5 I would guess.
-Tom

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Tim Zimmerman wrote:

For "pearl size sections" missing, don't even try to balance it. Just replace it. Balancing a blade makes sense for normal wear; it's not indicated for acute damage.
--
Bo Williams - snipped-for-privacy@hiwaay.net
http://hiwaay.net/~williams /
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You should not run the blade with that much damage. Get a new blade, send the bill to your friend.
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bw wrote:

Hate to be the bearer of bad news, but the odds are that the severe vibration that you are experienceing is not due to an out of ballance blade. When a mower hits an object like a root, or rock or other obstruction, it often bends the crankshaft that the blade is attached to. This happened to my parents Honda mower when my son ran it into a rock and the repair guy told us that it is a common occurance. In their case it required a fairly expensive repair, the replacement of the crank shaft AND a new blade. You can try a new blade, and maybe you will get lucky, but if he hit rocks numerous times, I expect that the vibration will still be there with the new blade. They don't make the motors on mowers with heavy enough parts to be mowing rocks.
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This is Turtle.
I take the blade off and bring it with me to Walmarts and go to the lawn mower area and match it up and get a new one for $9.95 and come back and put it on. Tring to balance a blade on a lawn mower with chunks missing is right next to impossible.
Now like Randy said it might be a bent shaft on the motor.
TURTLE
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wrote:

Your mistake was loaning the mower. Your "friend" owes you a new one, or at the very least should take it in for repair. You may have a bent shaft and in that case the mower is trashed.
You can buy a balancing cone made specifically for mower blades. These work well. Or, you can use the shaft of a screwdriver to balance it, but the cone works better.
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I use an old knife blade clamped in the jaws of a vise. I then balance the blade with the knife edge running across the center of the hole. Grind the edges to balance. You will never get the blade to sit stationary but you will see which end is heavy. If the mower is shaking enough to feel in your shoulders I suspect that the motor shaft is bent. Randy

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Randy Zimmerman wrote:

It might be worth removing the blade and running the motor to see if it still shaking or the shaft is visibly wobbling. If it is, then a new or balanced blade is a waste of money and/or time.
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Tom N wrote:

Certainly the first thing I'd do.
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Tim Zimmerman wrote:

If it is a serious wobble I'll put my money on a bent motor shaft rather than an unbalanced blade. I have a battery-powered electric sold by Sears but IIRC made by B&D and hitting a tree root with it left me with a bend in the motor shaft which was unrepairable leaving me to replace a very expensive motor. I'm a lot more careful now...
--
John McGaw
[Knoxville, TN, USA]
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Tim Zimmerman wrote:

It sounds like you have a bent shaft and certainly have a damaged blade that needs to be replaced not balanced.
--
Joseph Meehan

26 + 6 = 1 It's Irish Math
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Buy a new blade and give the bill to your friend.
Tom

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buy a lawnmower blade balancer, $5 on ebay.
i
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i felt the need to hear myself talk so i decided to add nothing to this conversation like the other 20 people before me.
nice fishing tim.
randy

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You can test the balance by hanging the blade from a nail or string and grinding as necessary, but if it has the chips you say, it wouldn't be out of line for your friend to buy you a new blade.
--

Larry Wasserman Baltimore, Maryland
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Replace the blade. A blade that has been that badly abused may have had its integrity compromised. You can bank on that blade being severly weakened. If you try to balance it and use it, you are running the risk of a catastrophic blade failure in the future, which means that it is possible that chunks of metal could come flying out from underneath the mower. It is possible that the shaft is bent; however, some lawn mower engines have small aluminum 'keys' that sit in slots machined into the shaft (or at least where there is a mechanical connection between the shaft and the engine). These are designed to fail if the blade strikes something hard. It happened to me once. I hit a metal culvert and the mower stopped dead and would not restart. Once the keys were replaced, everything was fine.

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Tim Zimmerman wrote:

Don't know how big "pearl size" is since pearls come in a lot of different sizes. You're going to have to do a lot of grinding to get it in good shape and balanced.
To balance it, just clamp a six or eight penny nail in a vice (horizontal) with about 3/4" sticking out. Or, pound the nail into anything and stick the center hole of the blade on it. You can get fancier but a nail works. Set the blade slightly off horizontal and grind until the side that is down always swings down (try each side slightly below horizontal).
Finally, you may have a worse problem than just chips in the blade -- the crank shaft may be slightly bent. Be sure you get the blade balanced well, because you need a balanced blade to tell if the crankshaft was bent.
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I dought it is the blade probably the rotor shaft, A new motor is in order but at the price of parts a new mower your idiot friend owes you. He wont be your friend now. And you wont loan out your stuff. My neighbor wanted to borrow my mower I said its broke, He borrowed someone elses and I heard him hitting rocks for an hour stalling his loaner mower.
Dave HVac electric motors dont have Crankshafts.
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dave must be smokin' crank to be so friggin stupid
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