B7800 front axle ball bearing question

[TheOldHokie]

You are not wrong in anything you have said.

But Kubota USA may be the one sourcing the replacement parts. And if some bean-counter gets an offer of 5,000 NSK badged bearings at $9 each instead of $10 each (s)he may well not be too picky about investigating the supply chain closely.

Again, I'm not saying that's what happened, just that it has been known to happen. Google "Counterfeit NSK bearing" produced reports of seizures of tens of thousands of counterfeits. Those are just the ones that got caught.

I know all about the counterfeit bearing problems. And for that very reason Kubota is not going to buy their radial ball bearings from a third party. The procurement guys not the bean counters will go straight to the OEM.

What the parts man in a Case/New Holland/Kubota/ dealership might do is another matter. But that bearing will not be in a Kubota package.

All that aside this is a case of servicing worn, damaged, and now user modified OEM parts. I would be really surprised if they are all "good" and one of the new bearings is "bad".

Dan

 

[TheOldHokie]

 

[TheOldHokie]

Looking at the parts diagram I would expect both bearings #40 abd #50 to be a press fit on the shaft as follows:

1. Assemble seal to axle and install in outer case half
2. Press bearing #50 onto shaft and into slip fit in case using shims as needed to eliminate endplay while make bearing flush with groove for shaft retaing collars.
3. Install retaing collars in groove on shaft and slide gear onto splined portion of shaft.9
4. Press 6305 bearing #40 onto end of shaft to retain gear and shaft collars.
5. Slide completed assembly into outer case with bearing #40 a slip in internal hub.
6. Bolt halves together locking everything down

That checks all of the normal design practice boxes.

 

[torch]

Looking at the parts diagram I would expect both bearings #40 abd #50 to be a press fit on the shaft as follows:

1. Assemble seal to axle and install in outer case half
2. Press bearing #50 onto shaft and into slip fit in case using shims as needed to eliminate endplay while make bearing flush with groove for shaft retaing collars.
3. Install retaing collars in groove on shaft and slide gear onto splined portion of shaft.9
4. Press 6305 bearing #40 onto end of shaft to retain gear and shaft collars.
5. Slide completed assembly into outer case with bearing #40 a slip in internal hub.
6. Bolt halves together locking everything down

That checks all of the normal design practice boxes.


View attachment 159787

I thought he was referring to the bearing at the bottom of "G120XX":

The bottom bearing had completely disintegrated and bits of the ball cage were going through the bottom gears.

Which is not to say it couldn't be a press fit too, but looking at diagram G1200, there is no retaining circlip for the bottom bearing, suggesting it was possibly press fit into the housing. The upper bearing is retained by an external circlip to the shaft below the bearing and an internal circlip to the housing above -- suggesting neither was a press fit. It's possible that the lower bearing was similarly a slip fit both internally and externally, given that design philosophy. I don't have a FSM for the B7800.

 

[TheOldHokie]

I thought he was referring to the bearing at the bottom of "G120XX":

Which is not to say it couldn't be a press fit too, but looking at diagram G1200, there is no retaining circlip for the bottom bearing, suggesting it was possibly press fit into the housing. The upper bearing is retained by an external circlip to the shaft below the bearing and an internal circlip to the housing above -- suggesting neither was a press fit. It's possible that the lower bearing was similarly a slip fit both internally and externally, given that design philosophy. I don't have a FSM for the B7800.

That was my first thought but that bearing is a 6304. The only 6305 I can find anywhere is #40 in the other diagram.

The outer ring of all of these bearings are presunably clearance fits in the housings to allow for assembly. Its the inner ring to shaft fit thats the question. In the case of Figures G120x and G125x I would expect the bottom bearing to be an interference fit to the shaft and the bearing and shaft would be installed/removed as a unit.

L

 

[Donystoy]

Interesting thread! When I overhauled both spindles on my B7200 I obtained all parts including bearings from the dealer. Nothing was press fit.

 

[TheOldHokie]

Interesting thread! When I overhauled both spindles on my B7200 I obtained all parts including bearings from the dealer. Nothing was press fit.

Yeah, I have that WSM and its an altogether different design with lots of very obvious sbap rings.

But your post prompted me to check the WSM for my L3901. That axke is very similar to the B7800. See the WSM page for the L3901 front axle below. As you can see the bearing retains all of the sliding components on the shaft and keeps the split collars that retain the axle captive inside the recess in the bevel gear.

 

[TheOldHokie]

Nobody will ever accuse Kubota of consistency. That hub design has been in use for at least 25 years and all of the older manuals have the same set if puctures and simply say "remove the bearing" with no mention or picture of of the puller.

I suppise engineering could have changed the fit in later years or maybe the WSM editors decided they needed to explain how

Dan

 

[torch]

Nobody will ever accuse Kubota of consistency.

So far in this thread:

B7200: not press fit.
L3901: press fit
B7800: one of each.

 

[TheOldHokie]

So far in this thread:

B7200: not press fit.
L3901: press fit
B7800: one of each.

How do you get one of each?

Dan

 

[torch]

How do you get one of each?

Dan

I was being facetious. The right bearing was a sliding fit but the left bearing is smaller.

 

[TheOldHokie]

I was being facetious. The right bearing was a sliding fit but the left bearing is smaller.

And that completes the circle.

The OEM parts on the left and right sides are the same. They cannot be different fits unless the engineers botched the fit calculation or one or more of the parts is damaged.

Dan

 

[Neil]

First, the new NSK bearing from the Kubota dealer did come in the plastic wrapper like the bearing shown above.

Yesterday, I set both hubs on the bench side by side and measured back and forth several times. The NSK side runs a solid 0.0002 smaller than the Koyo side with free fits that "feel" the same. Neither bearing just drops on. They both require some jiggling and fiddling, but they do bottom out without force.

These are bearings 040 on the parts diagram. Bearings 050 are a very free fit, just dropping onto the shaft. They are a light press fit into the aluminum housing. The two little retaining clips 060 also fit freely and are captured by a recess in the back of the ring gear when everything is assembled.

While I agree that calibrating the mic would be necessary if I needed absolute values, here I'm only looking for the relative difference between two extremely similar parts. I fail to see how calibration would improve this measurement.

 

[torch]

While I agree that calibrating the mic would be necessary if I needed absolute values, here I'm only looking for the relative difference between two extremely similar parts. I fail to see how calibration would improve this measurement.

It doesn't. The calibration is really only an issue if comparing to a published spec or value or if using two different instruments, such as an internal mic on the bore vs external mic on the shaft.

Dan wanted to compare your shaft diameter to the published spec of the bearing bore so of course to do that requires an accurately calibrated instrument.

Keeping in mind (I'd say "bearing" in mind, but I already used that pun) that even a calibrated instrument is subject to the conditions of calibration. Temperature (of both the instrument and the standard) in particular can throw things off a few tenths. For maximum accuracy the instrument and the part should be heat soaked at the calibration temperature for several hours and then held in one's hand for the minimum possible time when taking the measurement.

In reality, at the small diameters we are talking about in this thread, close is close enough. Even if the temperature difference was tens of degrees, the difference in accuracy is likely going to be less than 5 tenths. More of an issue if you were heating up the part during turning then trying to hit a finished dimension while the part was still hot.

 

[TheOldHokie]

Yesterday, I set both hubs on the bench side by side and measured back and forth several times. The NSK side runs a solid 0.0002 smaller than the Koyo side with free fits that "feel" the same. Neither bearing just drops on. They both require some jiggling and fiddling, but they do bottom out without force.

These are bearings 040 on the parts diagram. Bearings 050 are a very free fit, just dropping onto the shaft. They are a light press fit into the aluminum housing. The two little retaining clips 060 also fit freely and are captured by a recess in the back of the ring gear when everything is assembled.

While I agree that calibrating the mic would be necessary if I needed absolute values, here I'm only looking for the relative difference between two extremely similar parts. I fail to see how calibration would improve this measurement.

Calibration wont improve the comparitive measurement. I wanted absolute dimensions to try and determine whether bearung fit is supposed to be clearance or interference.

I believe that question is now moot - its supposed to be interference. If new bearings are not an interference fit the axles are worn/damaged and undersize. You can replace them or cross your fingers and hope to get by as is. New axles are readily available @ $265 each. A bottle of Loctite sleeve and bearing retainer is about $25. There are various Loctite formulations with different strengths and gap fill capabilities. You will need an absolute measurement to determine what size gap you are filling. ID tolerance of the bearings is 25.000/24.999 mm. Or you can just go big with 660.

End of story.

 

[torch]

View attachment 159860

Neat chart. I wasn't aware they had a product that would fill a 20 thou gap! That must be a diameter measurement, not radius, right?

 

[TheOldHokie]

Neat chart. I wasn't aware they had a product that would fill a 20 thou gap! That must be a diameter measurement, not radius, right?

Gap fill is diametral clearance. 660 is a paste and not something I would use. 680 is what's on my shelf.

Dan