Flail Mower Mott 72" Flail Mower bearing replacement & drive pulley spacing

[def38]

I have not had any experience with your application (Mott mower) but BMW motorcycles have a large bearing (called the crown wheel bearing) in the single sided swing arm rear drive system (called Paralever by BMW). This bearing is preloaded during assembly and rides in GL5 gear oil. In order to accurately assemble and preload this bearing, mechanics heat the bearing in an oven and chill the housing in a refrigerator. This allows the bearing to fully seat to zero clearance (bottom) without hammering or pressing. You might try chilling the shaft and heating the bearing before assembly.

 

[Jack Yuan]

Good Evening. I have an old Mott 72 flail which needed to have the cutter shaft bearings replaced. I ordered a pair of the M-702408 bearing + housing combos from Flailmaster. Housing itself looks the very similar to the old one, with three bolt holes that line up great and grease zerks on the housing face. However, the face that mates with the pulley sits proud compared to the old bearing.

This first picture shows the original bearing & housing:
View attachment 549421

And the new one mounted to the flail on the drive pulley side.
View attachment 549420

And the step of the process where I realized I had a problem. The shaft itself no longer goes all the way through the pulley:
View attachment 549422

I'm sure it's something I've done. Before I took it apart the shaft was pretty much dead flush with the outer edge of the pulley.

The cutter shaft doesn't seem to be shifted left to right. The first set of knives on each side are spaced evenly from the mower sides.

The bearings are supposed to come fully pressed in, but I suppose I don't know if its actually bottomed out against something in the housing.
Really wrenching down the bolt that holds the pulley might gain me smidge, but I don't imagine it'll be enough for the shaft to go fully through the pulley.

Any advice is much appreciated!

According to the third photo, this mower shaft end use key to mount the pulley. So after some years working, this area shape should have been changed. It is metal fatigue, quite usual. I suggest you use ruller to check if it is still perfect round, I guess its outer diameter has been changed, so you cannot insert this old shaft into a new pulley.

If it is not round, then cut somewhere if necessary.

I suggest you to get help from Mott engineer, manufacturer engineer should know what wrong it is.

 

[Zumdahl]

I'm putting the same pulley back onto the old shaft. Only change is the bearing and housing behind the pulley. Without the new assembly, the pulley sits flush with the end of the shaft and the let for fine. The new bearing assembly stops the pulley from going far enough on to sit properly.

 

[whirly]

I'm going to go out on a limb BUT have you mic'd the old bearing housing?

#1 in the drawing below looks more like the bearing I have on my Mott 72.

 

[whirly]

Check the bearing PN in the parts manual and you will see that it is 102792. I think they put the wrong bearing in the right housing. You could get by with the grease fitting on top.

 

[leonz]

Hello Mr. Yuan,

Please accept my apology for not posting about your earlier posting, the steel discharge guards that are the mounted on your flail mowers and other brands of flail mowers are the an excellent way to prevent accidental discharge of material to the front of a flail mower.

The mounting of these individual discharge guards/baffles/plates allows the discharge guards/baffles/plates to follow the ground contour ahead of the flail mower rotor to reduce the chance of having an accidental uncontrolled discharge of material.

I agree with you complete;y that link chains are a very poor way to control the potential accidental discharge of mowed material or an object contacting the flail knives or the spinning flail mower rotor.


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The longer hub that is in the bearing set that was sent to Zumdahl for his Mott Flail Mower is the incorrect open bearing and bearing flange mounting for his flail mower and that is why the gap occurs on his driven pulley.

Added to that the resulting gap will prevent the V belt drive from running true/linearly as the "True" center line of the drive and driven pulleys "X" axis will no longer exist.


They sent Zumdahl the wrong bearings in the wrong housings. The open bearing sets are a slip fit bearing that are restrained by the end bolt on each stub of the flail mower rotor in combination with the bearing washer that compresses against the inner race of the open flange bearing that are bolted to the side weldments of the flail mower.

The stepped hubs of the flail mower rotor act in concert with the inner races of the open bearings nesting together to hold everything in place once the bolts are torqued into tension and held with Blue Loctite.

Mr. Yuan, I again apologize to you for the tardiness of my reply to you.


They need to exchange them with him at no charge.

 

[Jack Yuan]

Hello Mr. Yuan,

Please accept my apology for not posting about your earlier posting, the steel discharge guards that are the mounted on your flail mowers and other brands of flail mowers are the an excellent way to prevent accidental discharge of material to the front of a flail mower.

The mounting of these individual discharge guards/baffles/plates allows the discharge guards/baffles/plates to follow the ground contour ahead of the flail mower rotor to reduce the chance of having an accidental uncontrolled discharge of material.

I agree with you complete;y that link chains are a very poor way to control the potential accidental discharge of mowed material or an object contacting the flail knives or the spinning flail mower rotor.


-----------------------------------------------------------------------------------------------------------------------------------------------------------


The longer hub that is in the bearing set that was sent to Zumdahl for his Mott Flail Mower is the incorrect open bearing and bearing flange mounting for his flail mower and that is why the gap occurs on his driven pulley.

Added to that the resulting gap will prevent the V belt drive from running true/linearly as the "True" center line of the drive and driven pulleys "X" axis will no longer exist.


They sent Zumdahl the wrong bearings in the wrong housings. The open bearing sets are a slip fit bearing that are restrained by the end bolt on each stub of the flail mower rotor in combination with the bearing washer that compresses against the inner race of the open flange bearing that are bolted to the side weldments of the flail mower.

The stepped hubs of the flail mower rotor act in concert with the inner races of the open bearings nesting together to hold everything in place once the bolts are torqued into tension and held with Blue Loctite.

Mr. Yuan, I again apologize to you for the tardiness of my reply to you.


They need to exchange them with him at no charge.

Hi Leonz,

Aha, it is mistake because of wrong parts, that's reasonable. It is always a big point to deal with so many parts.
There were nearly 50K different parts when I came to manage my business. After several years' effort, I cut down most of the old product line, now I only have nearly 10000 different parts numbers. I always believe it is wrong to expand product line too fast before you make it good enough.

Managing parts system is always a difficult work. Customers will never know how difficult it is. It is a team work from suppliers--->factory inside management --->seller, a long chain related to too many people. If there is any mistake happen in this system, the final result is that customer receive wrong parts, like Zumdahl.

 

[Zumdahl]

I've sent a note to Flail Master asking to swap out the bearings.

In the mean time, and now that we're on the topic of on discharge guards... The mower I'm in the process of playing with doesn't have either the front deflector shield, or the rear trash deflector. I've run it the mower for a few years now, really just to clean up the pasture two or three times each year. I'm not super worried about the quality of the cut. Other than having a tendency to get wound up with long grass it seemed to work fine. Taking a partial cut off the top mostly fixed that.

I've been thinking about attaching 'something' around the place as a rear shield. Extra EPDM roofing, old carpet, etc. but it looks like you can get replacement rubber deflector on ebay for $66 shipped.
Would a rear deflector improve the operation? Better cut quality etc? Or is it more of a safety thing to prevent rocks getting tossed out the back?

Looking at the parts diagram, there is also a large metal front deflector which I didn't even realize was an option. Anyone an opinion on if installing one would make a material improvement in how well the mower operates?
And if so, have a potential source for the part or ballpark of how expensive they are? 6' of steel can't be cheap, or inexpensive to ship. That piece may just be a pipe dream for something I'm using once or twice a season.

 

[whirly]

If you don't have any problems ... don't fix it.

I have an old Mott 72 with a rubber dam on the back. It works just fine in low grass but the heavy stuff doesn't move out the back as well as without the dam. I wind up having to slow way down to get through heavy/thick stuff.

No I didn't remove the dam. It was a great excuse to get an HST tractor.

 

[leonz]

Hello Zumdahl,

you can purchase the front foot guard and the rear trash deflector for your flail mower from flail master.

My catalog has old prices so it would only give you a ballpark figure the complete rear trash deflector package with mounting hardware for model 88 is 41.49

The front foot guard for the model 88 is $218.97 you need to purchase the bolts and washers and some blue or red loctite to
secure the bolts and nuts.