Kubota KX41 revs dropping when hydraulics are activated

JerryMT

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Kubota M4500, NH TD95D,Ford 4610
Jun 17, 2017
528
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The Palouse - North Idaho
Yes it occurs on all hydraulic functions but to varying degrees depending on the load - eg. raising arm drops RPM more than lowering arm, pushing the bucket drops RPM more than pulling the bucket.

Suction and return filters were both changed. Both were terribly clogged. Return was so clogged that it had pulled apart from the pressure. But replacing them hasn't made any difference.

I'm still trying to get hold of a pressure gauge.

Can anyone confirm that the steel block standing up at the end of the control block, which is connected to the return channel to the tank, is the relief/check valve? (see image). looks like the one in the manual.
The diagram in a previous post shows several relief valves; a1, a2, b1, b2, b3, b4, etc plus the relief ahead of the return filter. Getting a gauge on the return line as well as the high pressure line would also be helpful for diagnostics.

How long between hydraulic filter changes? What's the OEM recommended change period. What was the material on the filters?

Is the oil cooler functioning? is it hotter at the inlet line than at the outlet line? Using a laser thermometer, what is the temperature of the cooler inlet flow and the outlet flow temperature?

I'm starting to think the that you may have a contaminated hydraulic system. Maybe a clogged cooler is causing the hydraulic oil to overheat and break down but it depends on what material you have on the old filters and the temperature you measure at the oil cooler.
 

JerryMT

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Kubota M4500, NH TD95D,Ford 4610
Jun 17, 2017
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Fuel is premium diesel. Probably just a difference in colour between US and Australian standards.
Pre-IP return to the tank is definitely free flowing. It pours in there pre-startup.
"Pre-IP return to the tank is definitely free flowing. It pours in there pre-startup."

What about the return to tank from the IP/injectors itself?
 

GodHungry777

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Kubota KX41 with D1105 engine
Dec 23, 2022
35
5
8
Australia
"Pre-IP return to the tank is definitely free flowing. It pours in there pre-startup."

What about the return to tank from the IP/injectors itself?
Here's the flow from the top of the IP which runs up to the return line along the injectors and out the other end down to a T-junction that returns it and the pre-IP return back to the tank.
 

GreensvilleJay

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One ugly idea, I don't think has been posted, is the posibilty that the actual hydraulic pump IS damaged. Maybe it can't supply the necessary GPM at the PSI needed when asked ??

if the machine 'ran fine when parked', it probably has good compression, so not an engine problem. Considering how FILTHY the hy oil was...I'm leaning towards a real 'hydraulic system' problem.
 

GodHungry777

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Kubota KX41 with D1105 engine
Dec 23, 2022
35
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8
Australia
Update: Uncoupled Hydraulic Motor

OK, I've uncoupled the hydraulic motor to remove any effect of the hydraulics on the revs.
See video.
In my introduction I say that uncoupling the motor had stabilised the revs but then my test on camera completely disproved that as the RPMs were all over the place.
  • It still over-revs at even half throttle (WSM has Max Revs at 2400RPM)
  • It still takes for ever to increase or decrease RPM when the throttle is adjusted.
So, while we may still have a hydraulic issue, I think we need to sort out this unstable RPM issue first.

Here's what I've done so far:
  • emptied and cleaned fuel tank (had water, rust and gunk)
  • replaced fuel filters (clogged with water and gunk from tank)
  • replaced fuel lines (lines were brittle) -
  • tested injector pump - pumping fuel evenly from all three pumps. Tested straight from outlets and through injectors.
  • Tested fuel slider rail. Full and free movement.
  • had injectors tested - tested ok
  • bled injector lines
  • replaced engine oil and oil filter
  • replaced thermostat and coolant (thermostat was stuck open)
  • air filter had already been replaced - exhaust is clear
  • checked governor spring, forks and flyweight. Worn but nothing broken or missing. All free moving.
  • cleaned and flushed hydraulic tank, replaced both filters (both filters were very clogged), filled with new oil.

 
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GreensvilleJay

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Greensville,Ontario,Canada
I'm pleased you disconnected the pump ! though my back is still hurting just THINKING about HOW you managed to do that !!!
Engine sounds 'ok', but it has to be a 'governor' problem. 'slow to respond', 'overshooting' ,'lagging' all point to the guv control Perhaps the guv springs are 'worn' or the wrong ones ?
Any chance there's a missing 'guv to throttle' spring ? Something like the 'return to idle' spring on gas carb engines ? I'd lookup that engine online to see how it's all connected. Post the engine model number and I'll try to see it online.
 

GodHungry777

Member

Equipment
Kubota KX41 with D1105 engine
Dec 23, 2022
35
5
8
Australia
I'm pleased you disconnected the pump ! though my back is still hurting just THINKING about HOW you managed to do that !!!
Engine sounds 'ok', but it has to be a 'governor' problem. 'slow to respond', 'overshooting' ,'lagging' all point to the guv control Perhaps the guv springs are 'worn' or the wrong ones ?
Any chance there's a missing 'guv to throttle' spring ? Something like the 'return to idle' spring on gas carb engines ? I'd lookup that engine online to see how it's all connected. Post the engine model number and I'll try to see it online.
The engine in mine is a D1105-BH.

The heavy spring is the 'Governor Spring'.
The light spring is the return to full throttle 'Start Spring'.
 

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North Idaho Wolfman

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So you've had the front of the motor (gear case) apart?
 

GodHungry777

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Kubota KX41 with D1105 engine
Dec 23, 2022
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Australia
So you've had the front of the motor (gear case) apart?
Correct. Front all has to come off to remove the governor shaft.

This was from a few weeks ago when I pulled it out to inspect it. It's all back together now but no drama to pull it back out to replace if you're confident it is causing the issue.

 
Last edited:

JerryMT

Active member

Equipment
Kubota M4500, NH TD95D,Ford 4610
Jun 17, 2017
528
156
43
The Palouse - North Idaho
Update: Uncoupled Hydraulic Motor

OK, I've uncoupled the hydraulic motor to remove any effect of the hydraulics on the revs.
See video.
In my introduction I say that uncoupling the motor had stabilised the revs but then my test on camera completely disproved that as the RPMs were all over the place.
  • It still over-revs at even half throttle (WSM has Max Revs at 2400RPM)
  • It still takes for ever to increase or decrease RPM when the throttle is adjusted.
So, while we may still have a hydraulic issue, I think we need to sort out this unstable RPM issue first.

Here's what I've done so far:
  • emptied and cleaned fuel tank (had water, rust and gunk)
  • replaced fuel filters (clogged with water and gunk from tank)
  • replaced fuel lines (lines were brittle) -
  • tested injector pump - pumping fuel evenly from all three pumps. Tested straight from outlets and through injectors.
  • Tested fuel slider rail. Full and free movement.
  • had injectors tested - tested ok
  • bled injector lines
  • replaced engine oil and oil filter
  • replaced thermostat and coolant (thermostat was stuck open)
  • air filter had already been replaced - exhaust is clear
  • checked governor spring, forks and flyweight. Worn but nothing broken or missing. All free moving.
  • cleaned and flushed hydraulic tank, replaced both filters (both filters were very clogged), filled with new oil.

Per your hydraulic schematic, there are three pumps; P1,P2,and P3. Did you disconnect all of them?
I'll take your word that the rpm is fluctuating because I don't see it on your video. If that's true, I'd suspect the IP governor is the problem.
 

JerryMT

Active member

Equipment
Kubota M4500, NH TD95D,Ford 4610
Jun 17, 2017
528
156
43
The Palouse - North Idaho
Update: Uncoupled Hydraulic Motor

OK, I've uncoupled the hydraulic motor to remove any effect of the hydraulics on the revs.
See video.
In my introduction I say that uncoupling the motor had stabilised the revs but then my test on camera completely disproved that as the RPMs were all over the place.
  • It still over-revs at even half throttle (WSM has Max Revs at 2400RPM)
  • It still takes for ever to increase or decrease RPM when the throttle is adjusted.
So, while we may still have a hydraulic issue, I think we need to sort out this unstable RPM issue first.

Here's what I've done so far:
  • emptied and cleaned fuel tank (had water, rust and gunk)
  • replaced fuel filters (clogged with water and gunk from tank)
  • replaced fuel lines (lines were brittle) -
  • tested injector pump - pumping fuel evenly from all three pumps. Tested straight from outlets and through injectors.
  • Tested fuel slider rail. Full and free movement.
  • had injectors tested - tested ok
  • bled injector lines
  • replaced engine oil and oil filter
  • replaced thermostat and coolant (thermostat was stuck open)
  • air filter had already been replaced - exhaust is clear
  • checked governor spring, forks and flyweight. Worn but nothing broken or missing. All free moving.
  • cleaned and flushed hydraulic tank, replaced both filters (both filters were very clogged), filled with new oil.

Per your hydraulic schematic, there are three pumps; P1,P2, and P3. Did you disconnect all of them?
I'll take your word that the rpms are fluctuating because I don't see that on your video. If that is so, I'd suspect the governor mechanism in the IP.
 

GodHungry777

Member

Equipment
Kubota KX41 with D1105 engine
Dec 23, 2022
35
5
8
Australia
Per your hydraulic schematic, there are three pumps; P1,P2,and P3. Did you disconnect all of them?
I'll take your word that the rpm is fluctuating because I don't see it on your video. If that's true, I'd suspect the IP governor is the problem.
3in1

Instability is probably the wrong description. You're right that it's stable once it reaches the throttle setting. What I'm referring to is that when you set the throttle, it takes so long for the revs to get up or down to where you've set it that you need to keep make adjustments once it gets there to try get it to set at 2300RPM.
A good chunk of the 2 minute video is me adjusting the throttle just trying to get it to 2300RPM.
 

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North Idaho Wolfman

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Thanks for the video, it might explain what happened!
You pulled the gear off the fuel cam!
That gear should not have been removed!
Did it go back on the same exact way.
And when it went back on did you reline all three or 4 timing marks?
It sounds like it changed the timing of the fuel cam!

If you aligned it to only the gear next to it it almost certainly off.
These motors have a funny timing aspect is that all three or 4 marks only align every ~288 some odd rotations (I don't remember the exact number), any rotation in the middle of the cycle will not align the marks.
 
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GodHungry777

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Kubota KX41 with D1105 engine
Dec 23, 2022
35
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Australia
Thanks for the video, it might explain what happened!
You pulled the gear off the fuel cam!
That gear should not have been removed!
Did it go back on the same exact way.
And when it went back on did you reline all three or 4 timing marks?
It sounds like it changed the timing of the fuel cam!

If you aligned it to only the gear next to it it almost certainly off.
These motors have a funny timing aspect is that all three or 4 marks only align every ~288 some odd rotations (I don't remember the exact number), any rotation in the middle of the cycle will not align the marks.
Yes. Here's the video of when I got to that and started head-scratching. I concluded that they only lined up on certain rotations and marked them all at the point they were in this moment and reinstalled the same way they were prior to me pulling them off. I only removed the IP camshaft pulley, as it is all that was needed to access the governor shaft.
The issue we're chasing was the same before and after this exercise. I'm confident all went back in the way it came out.

Any thoughts on the condition of the governor shaft and flyweight movement from the video above?

 
Last edited:

North Idaho Wolfman

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Yes. Here's the video of when I got to that and started head-scratching. I concluded that they only lined up on certain rotations and marked them all at the point they were in this moment and reinstalled the same way they were prior to me pulling them off. I only removed the IP camshaft pulley, as it is all that was needed to access the governor shaft.
The issue we're chasing was the same before and after this exercise. I'm confident all went back in the way it came out.

Any thoughts on the condition of the governor shaft and flyweight movement from the video above?

Ok you didn't say, did you line up all the marks and make sure it was in time?
The bottom mark ( crank ) will be under the collar on the crank, slide it forward to see the mark.

The governor looks / sounds right.
 

GodHungry777

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Kubota KX41 with D1105 engine
Dec 23, 2022
35
5
8
Australia
Ok you didn't say, did you line up all the marks and make sure it was in time?
The bottom mark ( crank ) will be under the collar on the crank, slide it forward to see the mark.

The governor looks / sounds right.
I made sure it went back the same as how it came off.
Other research shows that the timing markings only line up correctly every 200ish revolutions or something so I wasn't going to start mucking around with that kind of complexity.
I only removed the IP camshaft gear (Top left) and replaced it how it was on reassembly.
I didn't remove the idler gear (center), valve camshaft gear (top right) or crankshaft gear (bottom). So none of them needed to be realigned.
 

North Idaho Wolfman

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Ok you didn't say, did you line up all the marks and make sure it was in time?
The bottom mark ( crank ) will be under the collar on the crank, slide it forward to see the mark.

The governor looks / sounds right.
I made sure it went back the same as how it came off.
Other research shows that the timing markings only line up correctly every 200ish revolutions or something so I wasn't going to start mucking around with that kind of complexity.
I only removed the IP camshaft gear (Top left) and replaced it how it was on reassembly.
I didn't remove the idler gear (center), valve camshaft gear (top right) or crankshaft gear (bottom). So none of them needed to be realigned.
I don't think your understanding what I'm saying.

How do you know they are right if you didn't align them?

It's possible that they were set wrong and you just put them back in that wrong alinement

It's run like this since you got it right?
So is it possible?
 

GodHungry777

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Kubota KX41 with D1105 engine
Dec 23, 2022
35
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8
Australia
I don't think your understanding what I'm saying.

How do you know they are right if you didn't align them?

It's possible that they were set wrong and you just put them back in that wrong alinement

It's run like this since you got it right?
So is it possible?
Theoretically possible but not likely in my mind.
But my assumption is that it can only be made out of time by human intervention. A gear isn't going to 'slip' a tooth is it? If that assumption is wrong, I'm happy to reconsider.
I can't imagine that the previous owner has had the front end off. It requires complete removal of all the ROPS, body work, radiator, etc.
All evidence so far suggests that the previous owner had not even changed the oil, fuel or hydraulic filters, so I can't imagine they've been this deep in.
Yes it's had the problem since I got it.
 

North Idaho Wolfman

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Ok, that's what I was going to ask was if it looks like some has gotten in there.
So that's a no, and your right no it's not going to jump time on it's own.

I've lost my place on this issue, so from the top:
Have you done a compression test?
This will tell a lot.

Have you had the injection pump and injectors professionally tested?
Because just because it put out fuel, it does not mean it's putting it out at the right psi.

I would safely say you have eliminated the hydraulics as any part of the issue as disconnecting it didn't make the engine run normally.

The slow rise in RPM and the drop in RPM when loaded are pointing to either the injection pump or the Governor.
Let me dig into the governor specs and adjustments and see if anything pops out, but I'm really leaning to the issue being in the injection pump or injectors.

Have we bottle feed the injection pump just to rule out any diesel supply flow possibilities?