hydraulic pump drive shaft fitting, sliding or press fitting?

[ErwinPWP]

Hi,

I have to replace the main hydraulic pump of my 3CX White Cab.
It was a pain to remove the drive shaft yoke from the pump drive shaft (Hamworthy, single type 1 1/4" diam. shaft).
I had to hollow the grub screw, disassembling the universal joint near to the pump and then pulling the yoke by a big pulley puller tool. After 30 years of mud and water, there was rust between the yoke and pump shaft.

I completely cleaned the yoke and now I'm able to slide it over the shaft of the new pump (by hand). It's not 'falling' but sliding.
Once the yoke has been fit over the new pump shaft there is a very very small amount of play. After tightening the new grub screw (which I've had to enlarge to M8 size) this play is gone.

Does anybody has experience with this fitting? Is the coupling between the pump drive prop shaft and the pump shaft meant to be a sliding fit or a press fit?

See attached pdf file (which I found on this forum). The yoke I mean is item 7 on the drawing.


Cheers

[Jeremy Rowland]

Hi Erwin; I would have thought that you could drill and tap another grub screw hole at 180 degrees to the one that is already in the coupling, you could also (assuming the shaft has not been hardened), carefully drill a small location for the grub screw to prevent any chance of anything falling off.
I would have thought that would be a sufficient method for securing the coupling, there are of course other methods that are shall we say less tactful.

Jeremy

[essexpete]

If the grub screw is ok and holding you might be ok but I would guess there should not be too much play sans the grub screw otherwise that will have to do a lot of work. Do I understand that you have increased the grub screw size?

[FOWLER MAN]

Hi Erwin,
The yoke is certainly not a press fit on the pump shaft.
It would be a tight push fit with the grub screw to secure it. The grub screw should be opposite the key, so perhaps not such a good idea to move it. Better to oversise it.
Use an allen socket screw if you can, a bolt head may be enough to un-ballance the shaft and cause vibration.
If you are worried that it is not a tight enough fit on the shaft use some Loctite bearing fit.
Fred.

[philwheelton]

If it slides on it should be ok as long as the grub screw grips they all are a pain to remove after a few years.

[Jeremy Rowland]

Hi Erwin,
The yoke is certainly not a press fit on the pump shaft.
It would be a tight push fit with the grub screw to secure it. The grub screw should be opposite the key, so perhaps not such a good idea to move it. Better to oversise it.
Use an allen socket screw if you can, a bolt head may be enough to un-ballance the shaft and cause vibration.
If you are worried that it is not a tight enough fit on the shaft use some Loctite bearing fit.
Fred.

Ahh I did not mean move the grub screw; I meant fit an additional grub screw which is something we often do here on some worn couplings which we repair at work.
I should have worded that a little better.

Jeremy

[ErwinPWP]

Hi All,

Thanks for your comments.

Just to be clear. I have over sized the original grub screw to metric M8 size. So my new grub screw (I use an allen screw) is on the same location as the old one just a little bit bigger.
Yes it was a pain to remove the original one. Due to a rusted head, my allen wrench had no grip on it ---> had to hollow/bore.
Hmmm to my opinion the original size is too small for it's application. Especially when you combine it with the bad environmental conditions like water and mud. Within a few years the small head is already ruined by rust!

The fitting I have now is an almost tight push fitting (is not freely sliding but once the yoke is over the shaft, there is a very very small amount of play).
I'll follow the advise of Fred to put some Loctite bearing fit to have a tighter fit. Just to be sure to avoid that the marginal play I have now will increase after xxxx operating hours. So just on top of the fixation by the grub screw because this screw pushes only at one point on the pump shaft.

[modelman093]

Fred's advice is spot on because what you are trying to do is eliminate fretting (movement between) the yoke and the shaft/key and a tight grub screw opposite the key plus Loctite will achieve this. Loctite bearing Fit has the added advantage of taking up any space between yoke and shaft and not only eliminating movement but also preventing the entry of rust producing moisture and air and hopefully making disassembly easier in the future. If the gap is not great and the job is being done in cold conditions Bearing Fit can be quite sticky and get wiped back during assembly - if this is a problem, assemble dry and with the grub screw removed and the hole upwards inject Loctite Penetrating Adhesive through the hole - it will work its way around the shaft.
As an aside the same goes for using appropriate grade of Loctite on threaded components - doesn't just prevent them working loose but fills the voids around the threads and prevents corrosion.
No connection with Loctite - just been a user of various grades since "discovering" it as a Caterpillar branded product in the late 70s!

[essexpete]

Fred's advice is spot on because what you are trying to do is eliminate fretting (movement between) the yoke and the shaft/key and a tight grub screw opposite the key plus Loctite will achieve this. Loctite bearing Fit has the added advantage of taking up any space between yoke and shaft and not only eliminating movement but also preventing the entry of rust producing moisture and air and hopefully making disassembly easier in the future. If the gap is not great and the job is being done in cold conditions Bearing Fit can be quite sticky and get wiped back during assembly - if this is a problem, assemble dry and with the grub screw removed and the hole upwards inject Loctite Penetrating Adhesive through the hole - it will work its way around the shaft.
As an aside the same goes for using appropriate grade of Loctite on threaded components - doesn't just prevent them working loose but fills the voids around the threads and prevents corrosion.
No connection with Loctite - just been a user of various grades since "discovering" it as a Caterpillar branded product in the late 70s!

Thank you for that useful advice, the rest of us may benefit from that!.