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Excessive Vibrations


longlegs's Avatar
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09-09-15, 10:24 AM   #1  
Excessive Vibrations

I recently had the deck off to change the belt, along with some other maintenance items like filters, plugs and lube and tire pressure. I also had the blades sharpened. I put things back together as they should be and cut the yard. This is when I noticed the excessive vibrations. I would to know what to look for as to the cause. I checked as as far as I could tell everything was as it should be.

can anyone shed some light on this?

 
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09-09-15, 10:33 AM   #2  
Last time I sharpened my blade I forgot to tighten the blade and it shook like crazy.

 
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09-09-15, 11:14 AM   #3  
If you find everything in place and tightened down check the blades for balance.

 
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09-09-15, 12:41 PM   #4  
I did get my yard cut, which takes about 1.5 hours. The cut was smooth and even.


how are the blades checked for balance?

 
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09-09-15, 02:34 PM   #5  
You can buy a blade balancer for a few bucks or simply place the blade on a round shaft screwdriver shaft. I clamp a screwdriver in a vise. Spin the blade gently and see if it comes to a to a stop in the same place each time or a different spot each time. An out of balance blade will usually show one side as heavier than the other and end up towards the floor.


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09-09-15, 05:02 PM   #6  
What is your mower ?

 
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09-09-15, 05:10 PM   #7  
In my experience I have rarely found any vibration due to unbalanced blades (unless extreme). Some like MTD that have the star pattern on the blade, if it is not seated correctly can be tight and level and still cause issues. Also possibly belt routing, if the belt is outside of a guide it should be inside of or such...deck not being correctly re hung....etc.

 
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09-09-15, 06:16 PM   #8  
it is a Poulan Pro with 22/46.

 
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09-09-15, 06:47 PM   #9  
I would suspect one of the blades is not matched to the star pattern on the shaft, allowing it to be off center.


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09-12-15, 12:26 PM   #10  
OK so I had the deck off again, checked the belt routing and that the blades were correctly seated and securely tightened which they were. I did notice though, that the left hand blade had some play in it and the right hand blade did not.

Also, the deck baffle as it called, what is the disadvantages of not having it installed?

 
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09-12-15, 01:04 PM   #11  
You mean you could rotate the left blade slightly where the right hand was snug? If that's the case was the play at the blade mount itself or farther up towards the pulley drive of the spindle?

If the play is at the blade mount that's likely where the vibration is - something is preventing the fixing bolt/nut from tightening down on the washer that holds the blade tight.

 
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09-12-15, 03:35 PM   #12  
A thin spot in the belt, a piece of debris stuck in a pulley, an unbalanced or off-center blade, bad bearings in a mandrel, bent crankshaft or jackshaft, loose engine mounting bolts, a pulley that has been pinched together a little bit in a spot where the belt rides can all cause vibrations.


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09-17-15, 05:07 PM   #13  
So today I replaced the lower bearing on the spindle, to correct vibration problem . I put things back together and give it a whirl. The vibrations is not quite as noticeable and seemingly normal. In using the I thought that it was making a buzzing type noise. Stopped and investigated, only to find that the deck is broken through at one of the bolt holes for that baffle. I have to get the deck off again, and get it to the shop to get a weld on the broken spot.

I also found that the idler pulley bounces around a bit when the blade is engaged

That's why I asked the question about the baffle earlier. The bolts on the baffle worked themselves loose, probably as a result of the vibrations. This resulted in the baffle getting caught up in the blades. The baffle is presently not on the mower, it has to be straightened and welded. I did some cutting today without the baffle and can't quite tell in difference in amount of discharge or appearance of the cut.

About the baffle, should I get


Last edited by longlegs; 09-17-15 at 06:21 PM.
 
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09-17-15, 07:42 PM   #14  
It's difficult to say from a distance because the only reading on the vibration is your own, so you have to use that as a starting point.

If there wasn't a vibration you would call excessive prior to the last work you did on the mower, and in using it the first time after the work was done you had the vibration, logic would say something in the maintenance items you worked on is the cause of the problem.
That would be the belt or sharpening the blades.

Maybe the belt has a problem. If the idler is bouncing a lot, the belt may be causing it.

The other thing would be out of balance blades. Simply taking off material and grinding out the dings of the blade is bound to be different on each end of the blade, which why you check the balance of them. They spin relatively fast and with the imbalance being out a possible 10 inches or more from center of the blade it can lead to a vibration within the parameter of that one blade.

But the problem can be more significant with two blades opposing each other. If the vibration directly opposes the other and one blade is fixed in its rotation to the other you get a bottom line of no vibration. But if one blade either begins in a position of its rotation or changes relative to the other, the vibration of one can magnify that of the other.

The best thing to do is balance both and eliminate that as a possibility.

 
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09-18-15, 07:08 PM   #15  
Usually, but not always, a bouncing idler is caused by a bad belt.


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