Interesting personal email from Kubota

[torch]

The cuts you see in the bolts are not "to weaken them" it's to provide a clean break that prevents a portion from getting bent out of shape and wedged in the slot.

Yes and no. You are correct that the purpose is to provide a shear line where they will break. The reason they will break there is because that is the weakest point. A grooved bolt is no stronger than a bolt of the groove's diameter, but an ungrooved bolt is stronger than a grooved bolt of the same diameter.

So, for example, if the manufacturer determined that a 1/4" Gr.5 bolt was required, the manufacturer could safely utilize 5/16" Gr. 5 bolts grooved to 1/4" to control the shear line location. However, if someone was to subsequently replace those with ungrooved 5/16" Gr.5 bolts then the force required to shear the bolt would be higher and could lead to damage elsewhere.

 

[Daren Todd]

It's very likely that it is a valid email.

I would be leary of getting an email from that address as well. Especially unsolicited. I've used similar links a couple different times for customer service issues. Would get an immediate reply from a an email listed as Customerservice@buisiness.com saying do not respond, we received your email, and someone will respond shortly. Here's your confirmation number. Follow up was always from an address with Personsname@buisiness.com.

Just randomly showing up in my inbox, addressed the way it was for the OP, would make me really leary if I didn't email them first.

 

[tcrote5516]

Following, and trying to figure out why your so upset Tom???
I don't find any of the subject misleading or wrong?
Tom, do you want to explain to me the problem?
If you want you can do it in a PM.

I assure you, I'm not remotely upset and hopefully my last post explained why I feel he is misleading. Going after product quality because the wrong components were used (no matter how they were acquired) simply doesn't make any sense.

Proactively bad mouthing a company's product or claiming the design is sub par when the problem stemmed from one persons mistake misleads other forum members who are just looking at their options. For example the person who wanted to know the differences between the 3pt and front mount that Dave recently posted his presentation on.

I'm just trying to balance his opinion with what I see as reality as an owner of that product. Dave seems like a very helpful guy but whether it's this issue or telling people tractors have brake lights he's human, we all make mistakes myself included.

 

[Mark15]

Yes and no. You are correct that the purpose is to provide a shear line where they will break. The reason they will break there is because that is the weakest point. A grooved bolt is no stronger than a bolt of the groove's diameter, but an ungrooved bolt is stronger than a grooved bolt of the same diameter.

So, for example, if the manufacturer determined that a 1/4" Gr.5 bolt was required, the manufacturer could safely utilize 5/16" Gr. 5 bolts grooved to 1/4" to control the shear line location. However, if someone was to subsequently replace those with ungrooved 5/16" Gr.5 bolts then the force required to shear the bolt would be higher and could lead to damage elsewhere.

This is true, but only to the extent if the shear force is applied over the groove. For example if a bolt is placed in double-shear (imagine placing a bolt across the end of two boards, spaced one inch apart, and then trying to force a 3rd board through the bolt, down between the other two). If the groove is outside of where the shear force is being applied, it will not weaken the bolt.

BTW: I'm new to the forum and learning lots already. Thanks!

 

[sheepfarmer]

Thanks for your Thanks!!
Would you mind posting a picture of the fan shear bolt area on your machine which has been trouble free. If we assemble a number of images of trouble free designs, those owners with problems will know where they need to alter their machines to start having your experience.

Dave M7040

I have the Kubota B2782B 63" snowblower, manual for serial no. 21503940 and up. It is different from the one in your picture. It calls for the fan shear bolt to be grade 5, part no. 70060-00726, 5/16 NC X 1 1/2 gr. 5 and lock and nut. The long shear bolt s for the augers are also grade 5. The ones in the blower are covered with orange paint but I think they also have the 3 lines on the head to designate grade 5. All of the dealer supplied fan shear bolts are grade 5.

As far as mine being a good example of trouble free, it is, but we have only had 3 snowstorms of 6-10 inches, that were worth getting it out to snow blow, and I was pretty careful with it because replacing a shear bolt would be difficult for me.

I'll add photos shortly.

 

[torch]

This is true, but only to the extent if the shear force is applied over the groove. For example if a bolt is placed in double-shear (imagine placing a bolt across the end of two boards, spaced one inch apart, and then trying to force a 3rd board through the bolt, down between the other two). If the groove is outside of where the shear force is being applied, it will not weaken the bolt

True, we have been assuming the grooves are aligned with the shaft/collar interface. If the grooves are in the wrong spot then it won't adequately limit the forces just as if there were no grooves.

 

[tcrote5516]

True, we have been assuming the grooves are aligned with the shaft/collar interface. If the grooves are in the wrong spot then it won't adequately limit the forces just as if there were no grooves.

It's tough to tell and way to cold to sit out there with caliper but I backed off the nut and it appears that the slot sits just inside the inner shaft. That makes sense because you want to maintain the bolt strength while insuring the inner section has a clean break point at the intersection of the two parts.

If it was aligned in the middle of the two assemblies then the worst that would happen is it would break at a lower force. Not great but it sure beats the alternative!

 

[sheepfarmer]

Just looking at the spare bolts and the auger shear bolts in place, it looks like the groove is as you say, at the junction. See pics added above.

The fan shear bolt has an ungrooved unthreaded section and a threaded section and it is less clear where that junction lies, but close to where those flanges would slide. Am slowly catching on to this discussion.

 

[sagor]

Yes and no. You are correct that the purpose is to provide a shear line where they will break. The reason they will break there is because that is the weakest point. A grooved bolt is no stronger than a bolt of the groove's diameter, but an ungrooved bolt is stronger than a grooved bolt of the same diameter.

So, for example, if the manufacturer determined that a 1/4" Gr.5 bolt was required, the manufacturer could safely utilize 5/16" Gr. 5 bolts grooved to 1/4" to control the shear line location. However, if someone was to subsequently replace those with ungrooved 5/16" Gr.5 bolts then the force required to shear the bolt would be higher and could lead to damage elsewhere.

You are correct. The other thing to remember is that these grooves are located exactly where the shear occurs, between the two planes of shear. That is, they are located at the point where the two rotating metal rods/shafts intersect.
Both my GR8 and GR5 shear bolts for my BX2750D are grooved down to approximately 0.26" and 0.23" respectively (close to 1/4") on 5/16" bolts. The shear strength is approximately 60% of the tensile strength of the cross section of the bolt where it shears.
And, like others have said, the shearing itself deforms some of the metal sideways, and having the grooves allows the deformation room to happen without exceeding the actual hole width. That is, the 5/16" bolt with a 1/4" area at the grove will shear sideways and still keep the sheared material within the 5/16" area so one can punch out the bolt without too much effort. It's all engineered this way on purpose.

 

[sagor]

Just looking at the spare bolts and the auger shear bolts in place, it looks like the groove is as you say, at the junction. See pics added above.

The fan shear bolt has an ungrooved unthreaded section and a threaded section and it is less clear where that junction lies, but close to where those flanges would slide. Am slowly catching on to this discussion.

I've measured the GR8 bolts in my BX2750D fan, and the thread itself is located at a shear point, but "just" for a 2-1/4" bolt. That is another reason they use 2-1/4" bolts. The inside diameter (narrowest point) of the thread is close to the same as the groove near the head, about 0.26". Thus, the thread itself provides the same effect as a necked down bolt for shearing purposes. The GR5 bolts are still machined down because the groove is about 0.23", and the thread narrowest point is probably closer to 1/4" or even 0.26" like the GR8 bolts. Seems the design of the GR5 auger bolts requires a bit less cross section area, hence they are grooved at the thread end as well to match.
Other shear bolts may rely on the threaded portion to provide the proper shear point thickness.

PS: All measurements are approximately what I remember, give or take a bit. The issue is, the narrowed down areas are different between the Gr8 and Gr5 bolts, and I'm sure are different for other shear bolts for other equipment. One can make their own shear bolts if you narrow down the same size and grade bolts at the same locations and at the same depth. The groove can be a bit wider, but should not be too narrow...

 

[Mark15]

Speaking of making your own grooved shear bolts. I saw a trick recently on YouTube that I am looking forward to my next opportunity to try. They called it a poor mans lathe.

Basically chucked the material into a drill press (or a drill clamped to a work surface). Turn on the drill press at a decent rpm, and then used a dremel type tool with a cut-off wheel to "lathe" the part. The Dremel was running as well, so it actually did the cutting, but the spinning part kept all the cuts symmetrical, kind of like clay on a pottery wheel. Looked like it actually worked extremely well!

Would probably work great for creating a grooved shear bolt if one needed to make one in a pinch.

 

[sagor]

Speaking of making your own grooved shear bolts. I saw a trick recently on YouTube that I am looking forward to my next opportunity to try. They called it a poor mans lathe.

Basically chucked the material into a drill press (or a drill clamped to a work surface). Turn on the drill press at a decent rpm, and then used a dremel type tool with a cut-off wheel to "lathe" the part. The Dremel was running as well, so it actually did the cutting, but the spinning part kept all the cuts symmetrical, kind of like clay on a pottery wheel. Looked like it actually worked extremely well!

Would probably work great for creating a grooved shear bolt if one needed to make one in a pinch.

Also an angle grinder with a thin cut off wheel will work in place of a Dremel tool. Bit more bulky of course. Or, mount the cutoff wheel on a bench grinder (if it can fit), and put the bolt on a cordless hand drill. Spin both until complete... (measure regularly)

 

[Dave_eng]

If anyone feels it is inappropriate for me to be on this forum making reference to the other popular forum which, although it has a segment for Kubota, covers all brands of tractors, please let me know here in public and I wont do it again. Since the specific shear bolt problem was the same but some information different, it seemed a way to gain more insight and hopefully a solution for those owners who are seeking answers.

I have been involved with this same topic on the other forum.
The thread was started by a guy having repeated shear bolt failures.

It has now been confirmed that the fan shear bolt being sold to him in a Kubota bag by his dealer is clearly a Grade 8 bolt with a deformed lock nut to keep it secured.

It has also been confirmed that he has the latest fan flange style shear bolt so in short, he has the newest design, is being sold Grade 8 bolts and is having repeated failures. He has been given suggestions on avenues to pursue

On the Kubota lawn and garden forum, there is a guy with a GR2100 who just recently managed to talk to a technical guy at RAD.

Again his comments might be informative to some.

The GR2100 owner has posted info on parts and upgrades being sold for Bercomatic Blowers. He says Bercomaatic and RAD have some history together so perhaps this an alternative parts and upgrade source.

Because I don't know how to direct you straight to these two threads I will provide screen shots which more skilled than I can use to find these.

Dave M7040

 

[Tooljunkie]

Breaking bolt story,not shear bolts but curious nonetheless.
Towtruck owner was breaking 5/8 grade 8 bolts on the wheel lift. Bought them by the boxful. I asked what he was using them for and why he was breaking them. So he showed me. Rais lift and lock it in place. Bolts were just long enough to grab the nut. I suggested a longer bolt so shank went through bracket and nut bottoms out. No threads in shear area. Didnt have a grade 8 long emough but he would try a grade 5. It worked. Bolt would distort but not pop and fall out.

Moving shear area away from threads utilizes the full strength of any bolt.

Understanding the headmarks to identify bolt strength is important, as already pointed out and grooving in shear area to prevent bolt locking in hole makes a lot of sense. Im getting the impression kubota has their shear bolt hardness all over the map, which can cause damage if dealt the wrong parts.

Customer buys parts expecting hes getting what he asks for. Parts guy walks in back and grabs what he thinks is correct and sells them without looking them up not realizing there is a multitude of shear bolts.

So find your part number,buy bolts that are engineered for your machine, and if dealer substitites he should be liable.

Parts technician note-its quicker/easier to grab what he thinks is correct than looking it up.

 

[Dave_eng]

Now that I knew the CustomerService email I received which started this thread was legit, I got brave and opened it.
See below:
Dave M7040


Good afternoon David,

We've received the following message from Radtech regarding your concerns with the shear bolts in your snowblower. We'd like to review further but would require a bit of additional info - namely the serial number of the product if possible, the name of your Kubota dealer and a phone number to reach you at.


Your company, who appears to make blowers for various tractor manufacturers, has produced a product being repeatedly talked about on tractor forums for having excessive shear bolt failures under normal operation. Now we have discovered, quite by accident, that a design change or update appears to have been done. I have posted pictures of the shear bolt details at the fan hub showing the difference.
Can you advise if this is a product upgrade available to customers who are having to change 5 or 6 shear bolts when blowing snow on their own property with no sign of and obstruction such as a rock which could have caused the failure.


Thank you,


Scott Johnson
Customer Service Representative / Représentant de Service à la Clientèle
Kubota Canada Ltd, 5900 14th Avenue, Markham, ON, L3S 4K4
NEW Toll Free Customer Service Line ***61479;1-800-405-6916
***61482;customerservice@kubota.ca***61472;***61496;www.kubota.ca

 

[torch]

Because I don't know how to direct you straight to these two threads I will provide screen shots which more skilled than I can use to find these.

Your first thread is here: http://www.tractorbynet.com/forums/.../372559-going-through-second-stage-bolts.html

Your second thread is here: http://www.tractorbynet.com/forums/kubota-lawn-garden/373235-kubota-gr2100-pto-speed.html

FWIW: I have a similar exposed gear box front-mount blower that came with my tractor with close to 20 years of use on it. The sheetmetal was lacework, rusted right through in many places, and the impeller fan blades were dinged and bent but the gear box is still intact.

 

[Dave_eng]

Your first thread is here: http://www.tractorbynet.com/forums/.../372559-going-through-second-stage-bolts.html

Your second thread is here: http://www.tractorbynet.com/forums/kubota-lawn-garden/373235-kubota-gr2100-pto-speed.html

FWIW: I have a similar exposed gear box front-mount blower that came with my tractor with close to 20 years of use on it. The sheetmetal was lacework, rusted right through in many places, and the impeller fan blades were dinged and bent but the gear box is still intact.

Any idea of what may be different between your blower and these whose owners are unable to get solved?

Did you note the comment by the GR1200 owner who said RAD told him the upgrade involved a new gearbox?

Who made the blower you have had great luck with for Kubota?

Would you please post a few pictures of it and do you have the owners manual with a parts page you could also post.

Dave M7040

 

[torch]

Who made the blower you have had great luck with for Kubota?

It is a B2550, c. 1994. I can't say for certain, but it appears very similar to the RAD unit pictures you posted.

Would you please post a few pictures of it and do you have the owners manual with a parts page you could also post.

The rebuild is not yet complete, but I have been photographing the process. You can see the uncommented photos here: https://picturehosting.verhey.org/Kubota/B2550/

I have the original owner's manual with parts diagrams. It's 37 pages and one of these days I will scan it and upload it to kubotabooks.com. In the meantime, the parts diagrams are freely available on Kubota's website.

The manual calls for "Bolt (1/4"NC x 1", grade 5, shear - with nylon lock nut) 70060-01075" for the impeller fan and "Bolt (5/16"NC x 2 1/4", shear - with lockwasher & nut) 70060-01338" for the augers. The impeller fan bolt is a plain ungrooved bolt protecting a single flange joint. The auger bolts are grooved to protect a shaft within the auger drive tube. I happen to have samples of each that are yet to be installed, you can clearly see they are both Gr. 5:

The impeller collar is affixed to the shaft with a 5/16" x 2" Gr. 8 bolt. There is no part number, just "OL" for "obtain locally", in the manual. It is clearly not intended as a shear bolt.

Also, the shear bolt part numbers and profiles are featured on a label affixed to the snowblower itself, so I don't know why anyone would get the wrong ones.

 

[North Idaho Wolfman]

Tractor by net references, Oh my what is OTT coming to!

If you want a good laugh, go to TBN and read the responses to the Brake light on a Tractor thread, it made me cringe, and nobody ever really answered his question.
Talk about drama!

I find this thread very interesting.

Torch, not that I'm disagreeing with you, but from my advantage point of the photo, those don't look like grade 5 bolts to me?

Would you take another picture of the heads strait on?

 

[torch]

from my advantage point of the photo, those don't look like grade 5 bolts to me?

Maybe because they are cad plated and shiny? A nice touch for use in a potentially salt-laden application.

Would you take another picture of the heads strait on?

Better?

Does anybody want a picture of them holding today's newspaper?