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vibrating blade

kleenmaster's Avatar
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09-29-03, 05:54 PM   #1  
vibrating blade

I was given a briggs & stratton stand behind lawn mower. The owner said blade vibrated alot when running. He said that it happended after hitting a rock. Someone else told me check the woodruff key. New to fixing lawn mower. Please advise.

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Terminator20's Avatar

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09-29-03, 06:48 PM   #2  
Take the blade off of the shaft. Tillt mower the direction oppisete of the muffler. Then you will find in the middle of the blade is a nut/bolt. Use the right sise socket and remove. After taking blade off, look to see if it is bent. If the ends have a bent look to them. Its normal because all mower blades are not completely straight from one to the other, otherwise it would not be able to cut. If the blade was bent that means that at least half of the blade will look bent. If it looks that way to you buy a new blade and install the same way you took it off.

After you work with mowers and small engines more often you will become more knoledgable on them and it will be easier for you to understand the different parts that make a mower and small engine. Don't feel bad, I used to be a bignner myself. I love working on samll engines though.

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09-30-03, 11:59 PM   #3  
Hello kleenmaster!

I agree that the blade is probably bent. Another possibility would be that the crankshaft is bent. Usually when this happens, the blade also gets bent. Check both and let us know what you find!

"Who is John Galt?" - Ayn Rand (Atlas Shrugged)

God bless!

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10-07-03, 10:31 AM   #4  
Did you figure this out? Have you been able to use your mower?

Sharp Advice's Avatar
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10-12-03, 09:08 AM   #5  
Hello: kleenmaster

Blades which cause a vibration are out of balance. Striking a stationary immovable object can cause the blade and shaft damage mentioned. As well as an out of balance blade.

Depending upon the damage, where the damage is and if it can be determined upon a visual check to be only to the blade, replace the blade with a new blade.

If the vibration problem remains, there is other damage which may not be repairable. If the problem is no longer there, the blade was in fact the problem.

How long the problem was allowed to continue could also present another problem. Engine shaft oil seal leakage is the least of the problems. Internal engine damage the worst.

How much vibration is selective and cannot be accurately determined nor described in a text only format like this. Slight vibration for a brief time is not serious. Excessive vibration over an extended time period is disastrous to the engine and dangerous to the operator.

To determine a blades balance without professional equipment, hammer a big nail partially into a wall beam so it is perfectly straight {horizontally} into a vertical beam of wood.

Put the blades center hole on the nail and do not allow the blades ends to come into contact with anything. Wait. The blade will reveal it's balance once it comes to rest.

The blade should remain horizontally level. If the blade tilts either way, the heavy side will be lower.

To correct the imbalance, grind off some material from the heavy end. End of the blade. Not the cutting surface, the end. Very important not to alter the cutting surfaces either. Both cutting surfaces should remain as identical as possible.

Remove a little material from the heavy end, little at a time and re test. Repeat the process of grinding off small amounts of material and rechecking the balance, until the blade will balance level.

The above process must be done after every sharpening also. The usage of a nail is just one do it yourself method. There are others that work equally as well and some that work better for the purposes of a diy blade sharpening task.

Regards & Good Luck.
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Last edited by Sharp Advice; 10-12-03 at 09:31 AM.
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