Kubota Letter/Cracked fenders/battery cover

[DickS]

Just installed the replacement part for the battery box/radiator cover. WOW! What a difference! I remember when I purchased the BX 24 my dismay over the poor fit and strength of the afore mentioned part. The Kubota dealer replaced it to my satisfaction.

On the issue of the broken fender, I have not experienced the problem and weigh 300#. Having said that, has anyone been proactive in engineering something which will reduce the potential for breakage. Perhaps some simple support in the weak area would be helpful. If there is a good home remedy, might as well take the precaution now rather than get into a taffy pull 5 years from now with a waranty claim.

 

[MessickFarmEqu]

Just installed the replacement part for the battery box/radiator cover. WOW! What a difference! I remember when I purchased the BX 24 my dismay over the poor fit and strength of the afore mentioned part. The Kubota dealer replaced it to my satisfaction.

On the issue of the broken fender, I have not experienced the problem and weigh 300#. Having said that, has anyone been proactive in engineering something which will reduce the potential for breakage. Perhaps some simple support in the weak area would be helpful. If there is a good home remedy, might as well take the precaution now rather than get into a taffy pull 5 years from now with a waranty claim.

There is more action happening at Kubota on this issue. I am not sure exactly what we're going to see, but its probably going to be in the form of a campain on all BX's. There is an additional kit that reinforces the old fenders with metal plates. From what I heard they are prefering this over the new fender design and even are considering these plates on the new fenders. Its all talk at this point, somthing should become offical shortly after the new year.

 

[Harry c]

Fender issue:

First: My company does not make plastic parts!!! No conflict here, just providing info!!

I've done lots of plastic work and designed molds for a variety of parts.
The fact that only some of the fenders crack indicates that the design is probably not the major culprit. The design might be less forgiving or robust than would be desirable but how much safety factor are you willing to shell out cash for? Overdesign costs $$

Likely, the real problem is that the plastic molding process has been inconsistent. As the molten plastic is forced into the mold it flows in different directions. The flow of the plastic is a huge part of designing the mold itself. Many computer programs exist to simulate this flow and allow the mold designer to adjust sprues and gates to control the flow. In a part of this size and complexity it is a serious task and "it don't always do what it should". As the plastic flows, several "fronts" are moving simultaneously. These fronts collide and the molten plastic must "knit" together to form a solid homogeneous surface. This knitting of the material is critical to the strength of a structural part. It can be inhibited by a number of processing factors such as temperature of the mold, temp of the melt, low injection pressure and presence of mold release just to list a few. If the material is at the wrong temp when it collides it will not knit. Injection pressure must be right or the material will not be compacted properly. Mold release is required to allow the part to come out of the mold. If improperly applied it can actually push in front of the flowing material and prevent the material front from knitting. The problem is likely not a part design problem as much as a processing problem. Companies like Kubota do not make these parts. They are purchased from suppliers that specialize in plastic molding. Kubota does not design the mold or the processing parameters. These companies have their problems just like every other company. Odds are that some fenders will crack immediately, others will last indefinitely. Just depends on the particular shot, etc.

As for the battery cover, mine was a poor molding job. It was likely ejected from the mold too soon resulting in warpage. Its questionable whether or not the mold was built to the right dimensions. Maybe the guy that designed the part just "blew it" on a dimension or missed an engineering change to related parts. That happens unfortunately. The new one is a more forgiving design and fits great.

Keep in mind Kubota is ultimately responsible for the quality and performance of the tractor. They've probably been hammering the supplier to get their act together since the first occurrence. The new fender design is probably an effort to overdesign the problem area so process variations don't result in breakage. Or possibly, just a mod to allow a visual identification of parts produced after some process change.

By the way, right now I'm working with Komatsu on a project for their newest BHL. Much larger machine of course. Interestingly, it uses plastic fenders, curved loader arms, curved BH boom...

 

[Dusty]

You likley would still be covered. They are really lax about the warrenty dates when it comes to known issues. Now if it where at 5 years, thats probably a different story.

Are they still covering broken air cleaner brackets? I have replaced 3 so far, and I just noticed that the present one is broken. Two were covered under warranty, and I bought the last one, since my machine was out of warranty. A known defect should be repaired or replaced for the life of the machine or until they fix the problem. They haven't ever fixed the air cleaner bracket problem, so what is the excuse ? Can't they engineer a air cleaner bracket that will stand the test of time??
Dusty

 

[Danilo]

Fender issue:


I've done lots of plastic work and designed molds for a variety of parts.
The fact that only some of the fenders crack indicates that the design is probably not the major culprit. The design might be less forgiving or robust than would be desirable but how much safety factor are you willing to shell out cash for? Overdesign costs $$

Likely, the real problem is that the plastic molding process has been inconsistent. As the molten plastic is forced into the mold it flows in different directions. The flow of the plastic is a huge part of designing the mold itself. Many computer programs exist to simulate this flow and allow the mold designer to adjust sprues and gates to control the flow. In a part of this size and complexity it is a serious task and "it don't always do what it should". As the plastic flows, several "fronts" are moving simultaneously. These fronts collide and the molten plastic must "knit" together to form a solid homogeneous surface. This knitting of the material is critical to the strength of a structural part. It can be inhibited by a number of processing factors such as temperature of the mold, temp of the melt, low injection pressure and presence of mold release just to list a few. If the material is at the wrong temp when it collides it will not knit. Injection pressure must be right or the material will not be compacted properly. Mold release is required to allow the part to come out of the mold. If improperly applied it can actually push in front of the flowing material and prevent the material front from knitting. The problem is likely not a part design problem as much as a processing problem. Companies like Kubota do not make these parts. They are purchased from suppliers that specialize in plastic molding. Kubota does not design the mold or the processing parameters. These companies have their problems just like every other company. Odds are that some fenders will crack immediately, others will last indefinitely. Just depends on the particular shot, etc.

As for the battery cover, mine was a poor molding job. It was likely ejected from the mold too soon resulting in warpage. Its questionable whether or not the mold was built to the right dimensions. Maybe the guy that designed the part just "blew it" on a dimension or missed an engineering change to related parts. That happens unfortunately. The new one is a more forgiving design and fits great.

Keep in mind Kubota is ultimately responsible for the quality and performance of the tractor. They've probably been hammering the supplier to get their act together since the first occurrence. The new fender design is probably an effort to overdesign the problem area so process variations don't result in breakage. Or possibly, just a mod to allow a visual identification of parts produced after some process change.

By the way, right now I'm working with Komatsu on a project for their newest BHL. Much larger machine of course. Interestingly, it uses plastic fenders, curved loader arms, curved BH boom...

The problem with the fenders IS a bad SUPPORT design. Look under the deck and see the deck suported by the plastic fenders. No way that will hold properly regardless of the "mold". Plastic fenders are ok as long as they are not providing support for a 200# and in some cases 300# people stepping up on them. Easy fix though while there are already holes in the deck and all that is needed is a piece of angle iron welded to the frame. We'll see if Kubota steps up or not. The "reinforced" fender will no doubt break again unless something is done.

 

[MessickFarmEqu]

Easy fix though while there are already holes in the deck and all that is needed is a piece of angle iron welded to the frame. We'll see if Kubota steps up or not. The "reinforced" fender will no doubt break again unless something is done.

This is exactly what the next remedy for the BX's is. From what I recall it will not require welding and will be field installable. Its alot easier and cheaper to do this than wait for the rest of the fenders to break.

 

[Dusty]

I always find it interesting that a person that has knowledge about how a part is manufactured, can describe the manufacturing process, along with a detailed explanation of how and why, is berated by someone that has a their own ideas, but doesn't provide any background to support their theory. America is a wonderful place where freedom of speech takes over for reasonable and intelligent thought processes. Throw enough iron at the problem and it will be resolved. Harry, you have my utmost respect for correctly describing the problem and the resolution of the problem.
Dusty

 

[TractorTodd]

America is a wonderful place where freedom of speech takes over for reasonable and intelligent thought processes. Throw enough iron at the problem and it will be resolved. Dusty

I wonder which thought process will be used by Kubota.

What is thought to be "reasonable and intelligent" by Dusty, or "Throw enough iron at the problem and it will be resolved" ?

To be continued........................

 

[swines]

Harry C has the facts on the problem. I owned a plastic injection molding machine that was used for "precision plastic parts" (almost an oxymoron). The maximum charge it would throw was 4 ounces - and we had trouble getting the molds correct for that machine specifically because of all of the problems he outlined.

This was long before CAD programs that would help you design the molds. We had to do everything by trial-and-error and rely on the experience of the mold maker. It was setup in part of my machine shop, and we found that even things like ambient temperature and humidity could affect the parts. Compensation was through changing the mold temperature, plastic temperature, and injection rate.

Now, you get into roto-molding of large parts - and that's another whole bag-o-worms...rotation speed, rotation direction, mutiple injection points, amount of material injected through each point, timing the injections....etc.

Makes punching metal parts on press + die look almost easy.

 

[jhr]

Any news on the brace kit? Anyone have one or seen one? I'd like to know for sure Kubota is really going to fix this prior to buying one of the new BX's. Thanks.