Broke Hydrostat twice? Why?

[dfkrug]

By the way, the hydraulics on my Korean-built Kioti tractor are made by Mita Oleodynamica of Italy.
I do not know if that includes the HST.

 

[dfkrug]

Could the worn/ eroded parts be made by a machine shop? If so it seams like you could
make it a working unit again and have a spare.

I would think about adding a temperature gauge to monitor the oil temp as well as a way to keep that lever from
accidentally moving to a position to cause the hydro to go into bypass.

Sadly, TYM is one of those companies who refuse to sell any HST subassemblies. I think this HST
would work fine if you just replaced the valve plates. They are a soft bronze-type material, and easily
scratched with a fingernail. Make one? Perhaps, but what material would you use?

My experience with JD and Kubota has been that they WILL sell HST subassemblies, but I do not
know if that includes all tractors. McCormick (Landini) would sell nothing inside their HST for my GX50H.

My Kioti parts book lists parts separately inside the HST, but I have not tried to buy any. Kioti
has a reputation for requiring excessive lead times for unusual parts, however.

 

[oldnslo]

And here is our problem.

Looking at the pump's valve plate, you can see erosion of the metal next to one of
the ports. This is the area where oil is pumped by the pistons at maximum pressure
into the forward port. The reverse port would have sustained the same pressures,
but it got used far less than the forward port, so it was not damaged.

My conclusion is that the oil overheated and boiled at the place where you see the
metal erosion. This was likely caused by the AUX detent valve being ON for an
extended period (perhaps minutes), which forced the full output of the implement
pump through the system relief valve.

DFkrug,
The oil going over the relief would also tend to aerate the oil which leads to cavitation which will erode metal just like in the picture. This would also explain the score marks on the motor since trash from the pump goes into the motor.

nice work and great right up

 

[dfkrug]

DFkrug,
The oil going over the relief would also tend to aerate the oil which leads to cavitation which will erode metal just like
in the picture. This would also explain the score marks on the motor since trash from the pump goes into the motor.

nice work and great right up

Yessir, that's a good point. Indeed, if you look closely, the surface of the wear area looks like inverted craters.

Thanks for contributing, OnS.

 

[Coyote machine]

So what about the broken spline, what does that indicate? Any part of cause and effect on this particular HST, or is the manufacturer rebuilding used/broken/returned under warranty, HSTs and selling them as replacement units, possibly?
Are you saying the reverse gearing did not get scalded by the excessively hot fluid from the AUX valve being on accidentally, without the OP's knowledge, and thus did not sustain the level of damage the forward gearing did?

It may be me, but I don't see the wear you refer to on the port(s) etc. I do see subtle scratches on some metals you showed and some darkening of the metal discs in others. Can you possibly circle the exact areas you're referring to, if not too much trouble, for us feeble minded older guys?:confused3:

 

[aczlan]

Are you saying the reverse gearing did not get scalded by the excessively hot fluid from the AUX valve being on accidentally, without the OP's knowledge, and thus did not sustain the level of damage the forward gearing did?

I would guess that foward got used more than reverse while the aux valve was on and that caused the wear (think of it as holding the plate in front of a sandblaster when this was happening, foward got held in front of it longer than reverse, so it wore worse).
This is the reason I really don't like idea of a detented aux valve...

It may be me, but I don't see the wear you refer to on the port(s) etc. I do see subtle scratches on some metals you showed and some darkening of the metal discs in others. Can you possibly circle the exact areas you're referring to, if not too much trouble, for us feeble minded older guys?:confused3:

Look at: http://www.tractorbynet.com/forums/...434394364-broke-hydrostat-twice-why-hst_6-jpg
Follow the right hand groove toward the left hand groove and there is an indentation/depression that is not there on the other side.

Aaron Z

 

[dfkrug]

I would guess that foward got used more than reverse while the aux valve was on and
that caused the wear (think of it as holding the plate in front of a sandblaster when this was happening,
foward got held in front of it longer than reverse, so it wore worse).

Yes, that's right. Depending on your usage, FWD may see 10x or 20x the action
that reverse does. Bob reports what may have been a gradual deterioration in
performance.

This is the reason I really don't like idea of a detented aux valve...

There is nothing wrong with detented AUX valves....I need them for running
a backhoe, or a hyd PHD, or hyd concrete mixer. Mine is very hard to
accidentally engage. That's really the issue.

On my first tractor, an old L2550 Kubota, the 3-point lever was easy to accidentally
put into relief at the top of its travel, and the range shift was super-easy to
knock into neutral when getting on/off the tractor. In the first case, you could
really hear the engine struggle. In Bob's case, not so much.

 

[aczlan]

There is nothing wrong with detented AUX valves....I need them for running
a backhoe, or a hyd PHD, or hyd concrete mixer. Mine is very hard to
accidentally engage. That's really the issue.

Perhaps they need a lockout so you have to push to the side in addition to forward or back to lock them in...
The idea just worries me with some of the drivers we have and their lack of attention to things like the sound of a relief valve bypassing.

Aaron Z

 

[MHarryE]

To me that cavitation erosion looks like the result of low charge pressure or air entrapped in the oil. The port plate wear shown in an earlier picture does look like lack of lubrication probably caused by oil getting too hot; however, my book on "Applied Failure Analysis" says overheated oil causes ash residue on the surfaces and I don't see that in the pic. I tried linking to an illustration of cavitation erosion but it linked to a purchase document rather than to the picture.

 

[Leejohn]

Sure was cavitation, I was going ask how it was getting air but Roy posted the reason. Thanks for taking the time to do this for us. It's very interesting and helpful. I almost forgot to thank Bob for getting the unit to you, Thanks Bob!!