torch
Well-known member
Equipment
B7100HSD, B2789, B2550, B4672, 48" cultivator, homemade FEL and Cab
I was having great fun digging holes when suddenly boom operation became rhythmically jerky. In my experience, sudden changes in operating characteristics never bode well, so I shut it down and started investigating.
I soon found most of a broken bolt lying underneath the PTO pump. Sure enough, it seems to have been securing the PTO adapter to the pump shaft. Once that fell out, the adapter started slipping on the pump shaft, causing the rhythmic action under load. And warming the adapter due to friction!
It's a socket cap head (ie: Allen head) machine screw, either 5/16" or 8mm (threads are gone so I'm not certain which). Harder than a grade 8 bolt, anyway. I'm not sure why it broke, but the rust vs the shiny bit on the broken end shows it was cracked most of the way through for some time before it failed completely, so maybe it was overtightened. It is not grooved like a shear bolt, and did not shear off at the shaft, it seems to have broken off at the nut.
I had some 1/4" gr. 5 bolts as spare shear bolts for my 3ph snowblower in the tool kit, so I threw one of them in there temporarily and finished up my hole.
The IPL on the Kubota website does not show the bolt. It shows a machine key on that pump shaft. I don't know if the bolt was missed on the drawing or the result of a design revision. I assume that at one point, the hydraulic relief valve was considered adequate protection, but have no way of knowing if the bolt was the revision, or the key. I would hope that Kubota has the latest version on the website, but who knows?
So my question is: should I replace the bolt with a grooved shear bolt?
I soon found most of a broken bolt lying underneath the PTO pump. Sure enough, it seems to have been securing the PTO adapter to the pump shaft. Once that fell out, the adapter started slipping on the pump shaft, causing the rhythmic action under load. And warming the adapter due to friction!
It's a socket cap head (ie: Allen head) machine screw, either 5/16" or 8mm (threads are gone so I'm not certain which). Harder than a grade 8 bolt, anyway. I'm not sure why it broke, but the rust vs the shiny bit on the broken end shows it was cracked most of the way through for some time before it failed completely, so maybe it was overtightened. It is not grooved like a shear bolt, and did not shear off at the shaft, it seems to have broken off at the nut.
I had some 1/4" gr. 5 bolts as spare shear bolts for my 3ph snowblower in the tool kit, so I threw one of them in there temporarily and finished up my hole.
The IPL on the Kubota website does not show the bolt. It shows a machine key on that pump shaft. I don't know if the bolt was missed on the drawing or the result of a design revision. I assume that at one point, the hydraulic relief valve was considered adequate protection, but have no way of knowing if the bolt was the revision, or the key. I would hope that Kubota has the latest version on the website, but who knows?
So my question is: should I replace the bolt with a grooved shear bolt?