Excessive vibration/shudder with flail mower

[super55]

My Mott SHD88 flail shudders only when it's bogging under load. I slip the shuttle into neutral and let the mower digest the clippings that are balling up under it. This only happens first mowing on a brushy field. Second mowing of the season never.
#2 on slow speed is critical in thick growth. We have a grass here in Mass called June Grass, thick and fine and hard to cut with ANY implement. Sickle, rotary, scythe, clippers.
Does your Mott have the 4-5" diameter drum the knives mount to? The 88 does and it looks like a beast to handle out if the machine.
Good luck and let us know how you make out.
Jim

Yeah it has the that 4-5" diameter solid steel shaft and the ends where the bearings are it tapers down about 2" I would guess. If the shaft I can about guarantee it is right on the end where it tapers down to fit inside the bearings.

Mine shudders terribly when I hit thick stuff even at a crawl speed and then as long as I keep the RPMS up around 540 it will keep shuddering and the tension pulley will be "donkey Kicking" until I drop the RPMs. After that I can bring the RPMs back up and be on my way but not usually too far before it happens again. The stuff I'm working in isn't terribly thick stuff either just about waist high grass but it has a tendency to like to wrap itself around the shaft. I thought maybe the grass was keeping the knives from flailing so I cleaned it all out but it really hasn't solved the issue.

I bought this because I heard everybody say flails were the way to go and I had heard Motts were pretty stout machines but I'm beginning to think I may have bought somebody else's problems instead.


Thanks for everybodys' input on this and giving me some directions on where to look.

 

[super55]

Found a few related thread in the similar post section. Ironically they were all Mott mowers that had the same exact problem. None of the threads had replies on what the culprit was.

Back to the topic. Where would a person go to get a shaft balanced and straightened? Do auto parts stores that have machine shops such as NAPA usually carry a lathe or something that can test balance and trueness or a machine shop that actually does metal fabrication needed? Does anybody have a ballpark on what such a service might cost?

Just by looking at the drum I can tell it is probably a pretty pricey part so if I had to get one from the manufacturer.

 

[leonz]

Hello super55,


Take the Mower to a car wash and make it spotless.

The Motts and others did have welded plate weights attached to the flail Mower rotors-
case in point my mathews has welded plate weights attached to the flail mower rotor,

The only ones with solid rotors are the forestry mowers which general;y have to have a
very heavy solid shaft for the carbide blades and the hammers welded to the rotor.

NOW your Mott flail mower rotor should be like everyone elses-HOLLOW with welded
end discs like mine.

Check to make sure that your bearings are locked in place and are not shifting from side to
side as that could also be an issue



It takes a lot to damage a flail mower rotor and that is why I want you to clean it up first before you get any further.

When bearings go bad with flailmower they will act like yours as the remaining ball bearings/worn ball bearings will settle into the bottom of the bearing race and when the rotor starts to spin up the bearings the rotor is being rotated by the belt and pulley and the stub shafts will spin on what remains of the ball bearings and a slower spin speed means less vibration of course.

if all the bearings are not in the race the end shaft will want to go where there is no support/ bearing balls.

DONT YELL,

remove the side slicers-all of them and the pins and then turn the Power Take Off on and spin it up to 540 rpm and see if you have the same vibration. if the same thing occurs the bearings are the usual suspect.


ANY big machine shop will know where you can have your rotor balanced on a high speed balancer. Your local power company could probably tell you right away who has a high speed balancer right away as the turbine rotor must be balanced using a high speed balancer.

if you have a good 4 foot steel ruler that is not warped you will be able to tell if the rotor is bent quickly but I still suspect its the bearings.

Dont lose heart yet throw the mower on its back, wash it and check it with the steel ruler or a good piece of solid square stock 1/2 inch by 1/2 inch if you do not have a 4 foot steel ruler.

 

[super55]

Leonz,

Beat you to on testing the mower without the knives on it. I checked it after I had to remove all the knives that were too big and slapping the housing. Ran it at full RPM and there didn't seem to be any issues with excessive vibration.

Actually even with the deck raised and running it at full RPMs there doesn't seem to be an issue. No vibration nothing but as soon as I put it down and start to go to work it starts to shudder. Knives aren't hitting the dirt so thats not the issue. What it really feels like is as soon as the knives breakaway when mowing grass and such that it is throwing the shaft way out of balance.

Bearings seem like a good first start. Im guessing that since these rotors work on centrifugal force that if there is a bad spot in the bearings or races that the rotor will drop right in it and stay there until I drop the RPMs down.

 

[bandaidmd]

Can you take off the belt and check the balance by gravity? If theres a heavy spot the drum will find it, its also a good way to fell how smoth the bearings are.

 

[leonz]

Hello super55,


Humor me a bit,


I would like you to remove several of the new side slicers 2 dozen or so, and find a place with an accurate scale digital or gram etc., and get back to me about it. If the knives are the same weight the bearings must be bad as that s the only plausible conclusion where several balls are missing in one or both bearings.

If you know any one with a dial indicator that is friendly or bribable with coffee and doughnuts perhaps they can come by and use the magnetic base mount dial indicator while the flail mower is on its back to check the trueness of the shaft stubs if they can be reached with the dial indicator arm. One or two slow rotations of the rotor will scream out that the bearings are either good or bad or the rotor is actually bent after you check the stub shafts UGH.

Be sure to check the bearing(s) locking collars if you have time, both of my bearings have lock ing collars on them.

 

[super55]

Im pretty sure the knives are all the same weight. I recently replaced all 140 of them with the same brand and size and they came in batches of 50.

When I put all the knives on the rotor I grabbed and tugged, pulled, pushed and rotated the rotor and the bearings felt stout and usually you can feel a grind. Had none of that.

Think I will turn this into a winter project and just slowly and meticulously try to go through everything. From the vibrations the seals on the gearbox are leaking (It still has fluid but leaks bad). There is also some cracked welds on the housing. The gearbox doesn't seem to be flexing from what I see but at this point who knows.

First thing will be checking trueness of the shaft though. My dad has a friend that owns his own tool and die shop I might see if they can see and give me a quote on checking trueness and balance of the shaft.

Once and if I can get this thing fixed I'll go ahead and post what I find out. Unfortunately just got too much going on right now with work so this project is going to get shelved for a few months.

 

[leonz]

Hello super55,




The more I think about this its the bearings for the following reason,
when we lost our first set of bearings on our Mathews the mower shuddered
and shook before it siezed after 30 years of use with regular greasing when in use.


No as far as the leaking gearbox issue is concerned you will have to decide whether
to purhcase a new gear box or simply replace the seals after you remove the cover
plate for the gearbox. It would be a good idea to change both seals in the input and
output side as a matter of good maintenance.

Once you remove the cover plate you will be able to determine the condition of the gear set
and decide whether you want to replace it or change the seals only after you have repaired
the bad steel with new steel and welds.

If I have asked you this before pardon the repeat question, does youe mower have the trash
doors that can be removed to improve the mowers ability to mow heavy brush and high grass?

 

[super55]

Thanks for all you help in the Leonz,

I think the bearings are a safe bet as well. Its at least a good place to start and go from there. The mower has no trash doors on it. Just a guard for the drive belt but I took that off when I was trying to diagnose what the problem was.

The gearbox never empties completely just to the point where there input and output seals are and I just fill it up before I use it but it's so easily accessible and such a quick job pending the seals aren't stuck I figured I'd knock it out of the way. It might wait until after I fix the main problem first though

 

[TXMF135]

Did you say it was a Mott/Alamo?
Go to the Alamo-Industrial website and download the OPERATOR's MANUAL.
When you have read that publication completely, determine what RPM the natural shudder will occur.
Remember to read the part about not operating your machine in the raised position as the PTO drive actually speeds up and slows down the shaft twice per revolution when the shaft is at an extreme bend.
Flailmaster.com has a replacement shaft if yours is bent. 88 is around $1700 +