Disconnect the spark plug wire and ground it if possible. Tip the mower up so the carburetor is on the high side. Use a block of 2x4 to block the blade - sometimes you have to stand on it. This allows you to put your weight on the wrench which will usually break it loose. Remove the old blade and install a new one. When tightening, block the back of the blade with your shoe. You could fiddle around with the old blade, but I'd trash it. In the future you can balance the new blade after you sharpen it.

I assume you already know this, but to balance it you merely grind off material from the cutting edge of the heavier end until the blade balances out correctly. To ensure the blade isn't bent just measure from the blade tip to the ground, then turn the blade 180º and remeasure the other tip, the measurements should be the same.

I have had the experience involving blade balancing in which the vibration increased after balancing. The mower is a John Deere JS 36C.
The problem probably began when mower blade hit a tent stake buried in the grass and sheared the flywheel key.
Everything worked after I replaced the key but the whole mower vibrated much like the one described.
Balancing the blade merely made the vibration worse.
I am going to replace the blade before the grass grows enough to mow.

You have a bent crank. No amount of balancing, nor a new blade is going to resolve the problem. Your engine is toast.

Attached a link to a "typical" blade balancer, you'll see them made from plastic, metal, etc.

FWIW, DO NOT "assume" a new blade is balanced. When I ordered mulching blades for my GT-5000, for whatever reason, checked them prior to installation. Two were perfect, one had to have quite a bit ground off to balance it.

Prior to balancing, sharpen, then scrape off any dried grass everywhere, as it does make a difference, then put on balancer.

Good luck,

Ev

Here is a link that might be useful: Typical Blade Balancer

"â¢Posted by ggoyeneche New Jersey (My Page) on Fri, Jan 30, 15 at 18:31

You have a bent crank. No amount of balancing, nor a new blade is going to resolve the problem. Your engine is toast."

The OP never stated he hit anything so by diagnosing a bent crank and changing the engine is a bit premature in my opinion. I'm not saying a bent crank can be ruled out, it's quite possible it is a bent crank. More details would be helpful such as when it first manifested itself and under what circumstances.

@itzbinnice:

I was referring to the post immediate above mine where "encee1424" said that he hit a tent stake. I could care less what happened SIX YEARS AGO by the original poster.

Read the train of posts more carefully before your pop off.

@ggoyeneche
Please accept my apologies, indeed I should have read the posts more carefully, you were not replying to the original poster.

However you may have chosen a better selection of words by reminding me.

This post was edited by itzbinnice on Sun, Feb 1, 15 at 7:40

I use a cone balancer. I too have had brand new blades come with new machines and not be balanced well at all.

That little cone balancer is one of the handiest things you can have if you operate power mowers. The key to blade maintenance is to take the blade off the mower and sharpen it BEFORE it gets all dinged up. That way you only need to file the cutting edges and check the balance. On the dinged-up ones, you'll need a bench grinder which takes off more material, but having the little balancer helps you straighten it out.

So, you need at least a 3" vise on a solid mount, a 10" flat mill file and the balancer. It would be great if you also had a bench grinder. Here's how I judge when to trash the blade, assuming there is no mechanical damage; the air foils behind the cutting edges wear out. When they get to about 1/16", the blade is toast. Other than that, if the width of the end of the blade gets to 1" from sharpening, its toast. Obviously if it suffers mechanical damage, like bending or breakage, its toast. Don't fool around with blades. Have a spare at all times and trash any blade you may have doubts about. If you have to ask yourself if you should sharpen it one more time, don't.

Now, do you know how to use a file? First, you put a file handle on it. The work must be solidly clamped - if you don't have a vise, you can usually clamp a blade to a fixed object like a work bench with C-clamps. Place your 'off' hand near the top of the file and approach the work at about a 45 degree angle. Also mind the angle of the cutting edge which is about 45 degrees. Lightly pressing with the off hand, file diagonally, using the forward stroke only. Lift the file and continue - never drag the file back across the work - its a one-way tool.

If you ever wondered what kind of steel a blade is made of it is spring steel. Some people LIKE ME wonder about the grinding temperatures and taking the temper out and things like that so it's related to spring steel. it's a tough steel that won't send out shrapnel so easily when it hits something and keeps its shape also.

trickyputt: If you're still talking about rotary lawn mower blades, I doubt you could be more wrong. International standards limit them to being made from very mild steel, severely limited in hardness so as to make it virtually impossible to break (shatter) under impact stress. The idea being to protect users of the mowers from injury from flying pieces of a shattered blade. The result is that most blades cannnot be honed to a very sharp (keen) edge severely limiting their ability to cut grass blades cleanly and eficiently. Some machining operations specializing in being makers of blades such as http://www.supertufmowerblades.com/about-us/, have come up with processes to enhance the wear and edge keenness capacities of the blades. The Supertuf folks use a coating / heat treating method. They coat the surface of the blade the buyer wishes to harden (harder = greater potential degree of keenness and durability of cutting edge), usually the underside in the cutting edge area of the blade. The coating contains a hardness imparting substance which the heat treatment causes to be infused into the surface layer of the steel creating a layer of harder steel. Another maker uses a more general surface hardening technique. In both cases the bulk of the crosssection of the blade remains that softer steel so it retains the user safety that insures.

The sort of hardening processes I mention are most clasically demonstrated in the centuries old Japanese Katana (Samurai sword) artisans' craft / art. https://en.wikipedia.org/wiki/Katana

I have heard that the steel generally has moved into a realm of softer, and I guess therefore tougher, steel. No doubt this involved lawyers. I have a little John Deere L130 and tend to just buy oem parts for it, and this link is where I got the spring steel idea, as I am certainly not a metal alchemist, just a blade sharpener-user. It looks like JD use spring steel. https://m.jdparts.deere.com/partsmkt/document/english/pmac/4382_fb_Lawn_Mower_Blades.htm

You know with the speed a blade is traveling. I ONLY USE THE ORIGINAL FROM THE MANUFACTURER. If you have a accident who are you going to call

Ghost busters??

Some generic parts I use, but never the Blade. Not worth it and my insurance would deny any claims.