Kubota R520 Compact Wheel Loader Intermittent LOUD Engine(?) Knocking Sound When Turning

[sae8425]

I hope some MUCH more diesel savvy forum members will be able to provide me with some much needed advice on this issue.

This compact wheel loader makes an intermittent noise that sounds like a LOUD engine KNOCK.

This VERY audible knock only lasts for perhaps 1.5 seconds (it is VERY brief – say half a dozen knocks or so).

The knocking sound ONLY occurs on tight turns (in both directions) at very slow speeds.

The knocking sound ONLY occurs once during a turn – turning circles continuously does NOT cause additional knocking sounds.

The knocking sound occurs when the loader is cold and when it is at operating temperature.

The loader makes NO abnormal mechanical noises or knocking sounds otherwise.

There is NO slop in ANY of the articulation or loader arms pivot points.

The LST seems to function properly, and without any lag.

The loader seems to have normal digging, lifting, etc. power.

The auxiliary hydraulic system works as it should (but it is only powering the quick attach coupler currently).

The machine doesn't overheat.

There are no fluid leaks and all fluids are at their correct levels.

The machine has about 4300 hours on it.


In NEUTRAL, using a stethoscope, I can't detect ANY inconsistent sounds emanating from any area of the engine at any rpm.

As the knocking noise ONLY happens briefly on tight turns, "live" troubleshooting might prove to be called for.

On the old Kubota compact wheel loaders, the driver's seat is attached to the top of the engine cover.

The engine cover would need to be removed to troubleshoot with a stethoscope while the machine was moving.

The seat would need to be attached to a support framework that would allow driving and troubleshooting at the same time.

To do the actual troubleshooting, the stethoscope would need an extended bendable probe that was 3 to 4 feet long.

Given the complexities of this process, live troubleshooting might be best done by a driver AND a listener (who sits where?).


I have NOT yet tried to look inside the engine/LST with my bore-scope.

Nor have I checked to see if the engine/LST mounting bushings are in good order (but nothing appears to be moving around).


I've thought perhaps the knock is fuel injection related, but wouldn't a fueling issue manifest itself at all times and RPM's?


I've owned plenty of cars with mechanical lifter cams and forged pistons with larger than normal cylinder wall clearances.

I KNOW what valve-train clatter, piston slap, and rod knock sounds like – at least in high performance gasoline engines.


What has me stumped is the intermittent nature of this knock, and it ONLY occurring on tight turns and for a VERY brief instant.

The internet is not being of any assistance in pointing me in any direction to do more troubleshooting.

I can certainly rig up a 2-seat troubleshooting system, but perhaps forum knowledge could make all this palaver unnecessary.


So; what do forum members suspect this abnormal mechanical knock is being caused by, and/or is a symptom of?

MANY thanks to any forum member who takes the time to share their knowledge about abnormal diesel engine(?) noises.

 

[The Peej]

Are you sure it's an engine noise? Have you checked the drive shaft universal joints? Only making noise when turning doesn't seem like an engine problem

 

[HarleyHappy]

Does this Kubota have the driveshaft that goes through a tunnel in the oil pan? If so, have you checked the shafts-joints and looked for rubbing or contact at the oil pan.
The front end could be worn at those hours and causing a shift, when turning tight.
With all your information and scope work, it should be relatively easy to determine whether this is motor or hydrostatic related or drivetrain.

 

[sae8425]

Many thanks for the comments and guidance.

No, I'm NOT sure the knock is coming from the engine; it's just a mechanical noise that jives with my gas engine experiences.

No, I haven't checked the driveshaft and/or universal joint(s).

No, the Kubota the driveshaft to the front section doesn't pass through the oil pan – and I don't recall seeing a tunnel/guard.

My experience with driveshafts and their joints is VERY limited – touch wood (my HEAD) I've had almost zero issues with either.

But, the VERY brief knock ONLY during tight turns does fit with the symptom of a likely driveshaft/joint/support bearing issue.

We're in the grip of a cold and snowy spell in NW PA currently, so it will take me a while to do any further troubleshooting.

However, I WILL update this thread after learning more, as I HATE threads that fail to include the outcomes/resolutions!

 

[InsleyGuy]

I don't have answer for you, but I do have a R420s. I would bet the issue is in the drivetrain, U-joints or splines. I'm puzzled that the noise doesn't follow through the hard turn.

 

[Tones]

Also check that the universals are correctly aligned (in phase). This can be easily corrected by slipping the spline section out and rotating to the correct position, if it's not to far gone.

 

[HarleyHappy]

^^^^^^ Please elaborate more on the “phase” of a u-joint.
I don’t believe I have ever heard the term regarding u-joints but think I know what you are referring too.

 

[Tones]

Here ya go

Avoid These Five Mistakes When Installing U-Joints | GMB Blog

Join Us As We Explore Five Of The Most Common Mistakes Or Difficulties Encountered When Installing U-Joints

gmb.net

 

[sae8425]

Again, many thanks for the further comments and advice.

Yes, the VERY short-lived loud knocking, which starts and stops during a hard turn, is what has me baffled as well.

These "hard turns" are not full on 42-degree maximum angle turns either, so the machine is not on its turn angle stops/limiters.

While I have heard failing u-joints in road vehicles, I have almost no experience with u-joints in off-road equipment.

My assumption is the brief motion of the worn part(s) redistributes the lubricant, which then stops the metal-on-metal contact.

Guess it is time to buy a factory workshop manual for the beast to better understand the suspected component layouts, etc.

I will check to see if the driveshaft is phased properly (this is a requirement that I do know about).

Weather is warming up in western PA and the show is melting off – perhaps I will be able to further troubleshoot later this week.

 

[B&B]

Again, many thanks for the further comments and advice.

Yes, the VERY short-lived loud knocking, which starts and stops during a hard turn, is what has me baffled as well.

These "hard turns" are not full on 42-degree maximum angle turns either, so the machine is not on its turn angle stops/limiters.

While I have heard failing u-joints in road vehicles, I have almost no experience with u-joints in off-road equipment.

My assumption is the brief motion of the worn part(s) redistributes the lubricant, which then stops the metal-on-metal contact.

Guess it is time to buy a factory workshop manual for the beast to better understand the suspected component layouts, etc.

I will check to see if the driveshaft is phased properly (this is a requirement that I do know about).

Weather is warming up in western PA and the show is melting off – perhaps I will be able to further troubleshoot later this week.

If you put a load on the front end can you get it to make the noise without driving, just turning the wheel?

 

[sae8425]

Good question!

I can't recall if turning the wheel from lock to lock when not moving forwards or backwards resulted in the knock occurring.

If the knock DOESN'T happen when ONLY the frame is articulated that further indicates a driveshaft related issue – correct?

I didn't try making a turn with the bucket full of dirt (moving or stationary).

It makes NO noise when digging straight ahead, or when raising a full bucket to maximum height while moving in a straight line.

Knocks when turning going forwards or backwards.

When I can do more troubleshooting, I will turn the wheel from lock to lock when not moving and listen for the outcome.

I will also fill the bucket with dirt and see if carrying a load makes any difference while turning (both moving and stationary).

Is there any other type of loading scenario that I should try to further troubleshoot this very brief knock?

 

[B&B]

Good question!

I can't recall if turning the wheel from lock to lock when not moving forwards or backwards resulted in the knock occurring.

If the knock DOESN'T happen when ONLY the frame is articulated that further indicates a driveshaft related issue – correct?

I didn't try making a turn with the bucket full of dirt (moving or stationary).

It makes NO noise when digging straight ahead, or when raising a full bucket to maximum height while moving in a straight line.

Knocks when turning going forwards or backwards.

When I can do more troubleshooting, I will turn the wheel from lock to lock when not moving and listen for the outcome.

I will also fill the bucket with dirt and see if carrying a load makes any difference while turning (both moving and stationary).

Is there any other type of loading scenario that I should try to further troubleshoot this very brief knock?

What is the model of machine? If applicable you can use the bucket to lift the front wheels off the ground and see if there's any play in the front end or spin them and see if there's any noise

 

[B&B]

Good question!

I can't recall if turning the wheel from lock to lock when not moving forwards or backwards resulted in the knock occurring.

If the knock DOESN'T happen when ONLY the frame is articulated that further indicates a driveshaft related issue – correct?

I didn't try making a turn with the bucket full of dirt (moving or stationary).

It makes NO noise when digging straight ahead, or when raising a full bucket to maximum height while moving in a straight line.

Knocks when turning going forwards or backwards.

When I can do more troubleshooting, I will turn the wheel from lock to lock when not moving and listen for the outcome.

I will also fill the bucket with dirt and see if carrying a load makes any difference while turning (both moving and stationary).

Is there any other type of loading scenario that I should try to further troubleshoot this very brief knock?

I had a john deere loader making a similar noise and it ended up being the driveshaft slip yolk was seized and it eventually wore the front pinion out. Articulating causes the shaft to extend and retract so that could be a place to look

 

[sae8425]

Loader is a Kubota R520 (not the "S" variant – I've read the R520S was simply the R520 with soundproofing (i.e. the "S" moniker) under the engine cover – which is also the seat support panel on all the earlier Kubota compact wheel loaders). Weighs 9,000 lbs.

I do know that the bucket will lift the front wheels off the ground, but I'm not sure the front and rear sections will stay straight when I get off to troubleshoot without preventing the steering wheel from moving (guess I'll have to bring some rope with me).

I've never had a driveshaft slip yoke seize up, nor lost an axle pinion, so I will CLOSELY examine the complete driveshaft system!

Assuming nothing is bound up/seized, come spring I will remove the driveshaft, fully clean all the bearing/sliding surfaces and replace the universal joints with ones that incorporate a Zerk fitting (no idea if the Kubota OEM joints have Zerk fittings).

And if the slip joint doesn't also have a Zerk fitting, I will drill and tap the yoke to add a Zerk fitting there as well.

Hopefully the factory workshop manual I ordered yesterday will be here soon (although I assume driveshaft slip yokes and universal joints are so generic that any WSM would hardly be necessary for diagnosis and troubleshooting purposes).

 

[HarleyHappy]

I really wouldn’t start taking stuff off and doing anything, until you actually find out what the issue is.
You may very well end up with something simple, no need to work on 5 different things and “hope” it fixes it.
Some people end up doing more damage than good sometimes.
Seeing your work, I will assume everything you do, is excellent.
Stay in the lane.

 

[sae8425]

Eons ago, while stationed in Europe in the military, I was involved with rallying – built Mini Cooper's (the REAL ones!).

I learned that preventative maintenance was MUCH better than towing broken down cars out of forests on rainy/snowy nights.

I fully intend to FIRST establish what is causing the very brief loud knock that only happens at the beginning of hard turns.

"HOPE" doesn't enter this process – I will methodically troubleshoot to find out PRECISELY what is wrong before doing ANYTHING.

Then I intend to take all APPROPRIATE steps necessary to ensure that the underlying issue(s) can be mitigated in the future.

If the issue is ONE failing universal joint, I will replace BOTH of them – and the replacements damn well WILL have a Zerk fitting.

If the issue is a sticking/seized slip yoke, properly cleaning out the splines requires removing the driveshaft.

If the slip yoke doesn't have a Zerk fitting it would be prudent to add one during the clean out, examination, and re-greasing process.

If the driveshaft has to be removed, replacing BOTH (20-year-old?) universal joints at that juncture would also seem to be prudent.

The "LANE" is not suffering preventable machinery maladies – "wear" happens, but it IS reasonably foreseeable and resolvable.

 

[HarleyHappy]

Okay then.

 

[sae8425]

Well; the Kubota Service & Parts Manuals have arrived, and I've been able to do some more troubleshooting.

I ran every test suggested by forum members to no avail.

ONLY difference was with 30-degree warmer weather the knocking during turns was replaced by knocking when going straight!

So; out came the tarps, foam pads, and LED floodlights to illuminate the drivetrain and dirt/mud covered underside. BINGO!

The problems appear to be the rear differential output yoke (Kubota calls this a "Clamp") and the corresponding universal joint.

This universal joint is shot (but I've seen LOTS worse). Rectifying this issue is straightforward (assuming removal is trouble free).

The FAR bigger problem however is radial movement (perhaps .025") of the transmission/rear differential output yoke.

Based on illustrations in the Parts Manual (the Service Manual doesn't cover ANY of this), the movement could be due to –

Worn yoke splines

Worn pinion splines

Worn seal in the transmission case behind (around?) the yoke

Worn taper roller bearings supporting the pinion shaft

A loose fastener (there is at least 1 bolt & 1 nut directly involved in the pinion/yoke assembly), PLUS some washers (I think).

And I guess it's always possible that the movement has caused some wear in the differential/transmission cases/housings.

So; it's off to Kubota armed with the part numbers (and a foam pad to fall on if I faint due to "price shock").

Obviously, I now need to start dismantling, and do a fair bit of cleaning, to determine the full extent of the wear/damage.

I'd rather be dealing with an engine knock than have to delve into this drivetrain! Sucks to be me right now.

Any further advice or comments regarding these issues would be welcomed.

As I stated earlier, I will continue to update this thread as/when I learn more.

Again, MANY thanks to the forum member who have taken the time to share their knowledge.

Oh yes; any forum member know of a Kubota R510/520 being stripped for parts anywhere? This includes outside the States.

 

[HarleyHappy]

While I wouldn’t expect it to be too bad but likely if it were a bearing or seal, it should probably be leaking.
Not sure but 25 thou of movement doesn’t sound that bad, might be as simple as tightening a nut to the spline.
Yokes do wear out though, I have had to replace quite a few yokes on driveshafts over the years, especially on shaker tables.
They tend to go through u-joint quite a bit.

 

[Simon C]

Even some main bearings can have up to 0.010 clearance so for a yoke to move up and down 0.025 is probably still going to work. As Harley Happy said might be able to tighten the yoke securing bolt or nut.
Simon C