John Deere snowblower wobble solved (balanced)

[JCByrd24]

I recently did a custom front mount of the very common 47" John Deere quick-hitch snowblower on my Yanmar 186D. In doing some research on this snow blower I found a few references to vibration issues, some from the excessive u-joint angles that Deere corrected with a CV shaft and others clearly related to the augers, a side to side wobble most noticeable when the blower was raised. Given that, and my previous project balancing my rear mount blower, I decided it wouldn't be much work and would be worth while to take the blower apart and balance everything, change the gear oil, check on all the bearings and overall condition of the used blower.

It was a good thing I did. I found all the bearings were less than perfect and one on the end of the auger shaft was loose and the inner race had been spinning on the shaft and had worn it about a 32nd of an inch. I did a weld build up on the shaft and chucked it up in the lathe and turned it back down. It was my first time turning something 4' long, so I made a bushing for the far end of the headstock to keep the shaft from whipping around, worked great.

To get to the point, what I found on balancing the augers made perfect sense. Basically the impellers may have been designed to be statically balanced when combined but each is grossly imbalanced opposite of each other. When spinning the ends vibrate opposite of each other and the thus the wobble. The shaft spins slow so it's not really a big deal but the bearings have to go through the cyclic loading unnecessarily. I only took a pic of one of the augers, this one is the longer one (the impeller is off center). You can see in this pic about 3" of 2"x3/8" flat bar added onto the stock counterweight. There was roughly 2" more on the back side of the counterweight that you can't see.


The other impeller the counterweight was in the totally wrong place. I could've cut it off, but instead I just added some weight to a flighting support on the opposite side, about as much as the other.

Here's a closeup of my balancing rig, well half of it. A couple of common small bearings pressed into larger aluminum discs to reduce friction. Seals and grease removed from bearings and replaced with a light oil. Needs a shaft to fit whatever you are balancing. All the Deere stuff is 1" so had it laying around. Could've used the Deere shaft itself but it was a little pitted and had keyways cut out of it. Ignore all the grease. Previous owner apparently loved grease fittings and anti-seize but didn't know how to take care of bearings.


This method on my impeller can pick up pretty small changes in weight. A 1/4" nut placed on one of the impeller blades after it was balanced would cause rotation. The impeller by the way had some vibration for sure but nothing too bad. The blades were just stitch welded to the hub plate so first I filled in between the welds on the light blade. That wasn't quite enough so I added a couple of inches of weld on the opposite side as well.

 

[Dave M7040]

Please don稚 mistake my comments for criticism as I welcome your reaction to my comments.

In the 1950痴 and 60痴 we motorcycle riders would balance our British bike痴 wheels and tires using a similar method. You would get them unto a low friction support or a level support where it rotated on its own bearings which were free of lube, spin the wheel and note where it stopped. If it repeatedly stopped in the same place you assumed the bottom of the wheel was the heavy spot and would add weight to the opposite side. You repeated the process until the wheel stopped in random spots.

For my cars, I had a bubble balancer where the tire and wheel assembly were placed on a horizontal pivoting hub with a bubble level in the center. You would add weights as necessary to get the bubble centered.

In both these instances the third dimension of what you were balancing was not considered. i.e. the balancing was not dynamic. Usually the result of the balancing of either the motorcycle or the car was far from perfect.

Trucks are frequently having their frames lengthened or shortened after they leave the factory to accommodate various boxes and mixers. This necessitates lengthening or shortening the driveshaft.
As you would know, the driveshaft on a truck is a long rotating shaft. These shafts have to be dynamically balanced. Weights have to be added along the length of the shaft to accomplish this.

I was doing some simple calculations to see how fast the typical snow blower auger rotates. I assume on your blower the gearbox is between the two halves of the auger where larger blowers have a bevel gear box behind the fan. I am certain that the basic dynamics of either two stage style are the same when it comes to fan and auger speed.

The main bevel gear box is a 1 to 1 to 1 gear ratio. The input turns once, the fan turns once and the sprocket to drive the chain which drives the auger turns once.
The sprocket driving the auger has 12 teeth and the sprocket on the auger has 50 teeth. Therefore the auger will turn at a ratio of 4.25 rpm slower than the pto.

For a pto speed of 540, which is the typical operating rpm of the tractor pto, the auger will be turning at 540/4.25=127 rpm

For comparison consider a car with 205 55R16 tire and wheel assembly. That tire will rotate 811 revolutions per mile. At 60 mph the car is traveling one mile each minute. Therefore the tire and wheel assembly is rotating at 811 rpm.
If we move forward from the tire and wheel assembly to the differential, a typical rear drive differential has a ratio of 3.25. Therefore the 811 rpm of the wheel becomes 3.25 x 811= 2635 rpm of the driveshaft.

What I have done is to convince myself that the rotating speed of the snowblower auger at 127 rpm is so slow that balancing is not critical.

Are you balancing the fan which would be rotating at 540 rpm?

As you are randomly picking a spot along the length of the auger to add weights to achieve a static balance, do you think you could be creating a dynamic imbalance as the location of the added weight could be completely wrong.

I wish I knew how to operate a lathe!

Dave M7040

 

[JCByrd24]

Dave, thanks for your interest and no offense taken. I think both I and JD would agree that this balance of the augers is not critical. Your guess was close, by spec the augers spin around 250 rpm IIRC. What has been a common compliant on the newer models is the side to side wobble, and as mentioned what I found is what you describe...that being, the augers appear have been designed to be somewhat statically balanced when combined, but each end individually was grossly out of balance in an opposing manner. I would concur with you that my static balance was not anywhere near the end result of a dynamic balance, but I expect when I get my bearings in the mail and reassemble I will have solved the side to side wobble as at the very least I have halved the error by balancing two individual sections of auger instead of 1 long assembly. In other words, I think I proved that my blower was already in the situation you described and my symptom of the side to side wobble will be reduced.

With regard to the impeller, this front mount blower by spec spins at 950 rpm, and I'm running it more like 1050 rpm so we are in 100% agreement that this is where things are really critical. As mentioned I had much less work to do in this area and only added 3" or so of weld bead. The impeller is much less shaft like then the auger, so I think the static balance will prove quite effective. It did on my rear snowblower, which while designed to run at 540 rpm I ran at 1000 rpm for a few seconds just to test the balance and it ran as smooth as silk. I think even 1000 rpm in small shafting is not considered high speed with regard to the need for precision balancing.