Ghost in the Machine? BH77

[bbxlr8]

Hi all - Need advice on my BH77. Not sure what is going on or if I have a real problem or not.
Read all previous threads I could find and none seem to have this issue without a lot of hours etc.

Last Sunday out of the blue the BH boom would not hold and visibly, sagged, losing pressure when running. Did it consistently over the course of 2 hours run. Would operate fine but drooped. If I estimate, it was about an inch every 20 seconds or so. Never any issue before. Oh, $h)# !!

Here is the background:

• L2501 with 190hrs prob about 60% BH time if I had to guess.
• Did 50hr maint. with full hyd change for my own peace of mind (conservative). Used K filters & fluid.
• Use it pretty hard as I have rocky ground and a few major grading projects over time. To that end, had the BH on/off several times in succession over the last two months using rake & BB.
• Always careful about contamination & cleaning connectors.
• H. Fluid is in the middle of the sight glass.

Read about it in archives - could possibly be the cylinder leaking, the pressure valve or the lever spring adjustment. Specs are supposedly 2" per hour leak down (@ normal hyd relaxing). Got that deep pit of the stomach sinking feeling as I just hit the 2-year mark and ironically filled out the Kubota Co. survey on Saturday (you can't make this up!)

MON morning I called service @ my dealer where I bought it to ask. Was told it was out of warranty on Friday, but to bring it in and he would try to see what he could do (no promises but fair). I don't have a trailer and $300 transport and they have"weeks" backlog. Looked at uhaul specs w/car ramps a @ 41" min.

Go out to measure the tire track (knowing it wouldn't fit) , pull tractor out and check it again - It showed NO signs of doing so even at low idle or off - left the lock off and came back 30 min later - nothing!!
I saw some had this issue intermittently where they theorized that some particle or contaminant gets caught in the valve and then flushes out...

WTH...is there really a ghost in the BH or just a fluke? Common sense says move on. I used it for another few hours Tuesday and all good. But, I don't want to be stupid if I should get it into the dealer now rather than sticking my head in the sand and have expensive repairs soon after. Have lots of work planned in the next several weeks before Memorial Day.

What do you all think?

 

[nbryan]

Common sense says.... carry on.

The only thing I'm curious about is if there's any difference in that boom sag occurrence, frequency or rate with the hydraulics cold vs hot?

Pop off the control valves cover plate and look at the cleanliness, tightness, clearances, and alignment of the control linkages now its been worked seriously for a while. Any tightness or binding resulting from loose or misaligned control linkages could cause your issue.

My BH77 valve linkages had pins loose and some binding going on, causing major sloppiness in operation. I also found the levers were actually hitting the cover plate before full valve motion, too. Left the rubber boots on but the plate off now permanently. No sagging occurrences yet that I've noticed.

 

[TheOldHokie]

Hi all - Need advice on my BH77. Not sure what is going on or if I have a real problem or not.
Read all previous threads I could find and none seem to have this issue without a lot of hours etc.

Last Sunday out of the blue the BH boom would not hold and visibly, sagged, losing pressure when running. Did it consistently over the course of 2 hours run. Would operate fine but drooped. If I estimate, it was about an inch every 20 seconds or so. Never any issue before. Oh, $h)# !!

Here is the background:

• L2501 with 190hrs prob about 60% BH time if I had to guess.
• Did 50hr maint. with full hyd change for my own peace of mind (conservative). Used K filters & fluid.
• Use it pretty hard as I have rocky ground and a few major grading projects over time. To that end, had the BH on/off several times in succession over the last two months using rake & BB.
• Always careful about contamination & cleaning connectors.
• H. Fluid is in the middle of the sight glass.

Read about it in archives - could possibly be the cylinder leaking, the pressure valve or the lever spring adjustment. Specs are supposedly 2" per hour leak down (@ normal hyd relaxing). Got that deep pit of the stomach sinking feeling as I just hit the 2-year mark and ironically filled out the Kubota Co. survey on Saturday (you can't make this up!)

MON morning I called service @ my dealer where I bought it to ask. Was told it was out of warranty on Friday, but to bring it in and he would try to see what he could do (no promises but fair). I don't have a trailer and $300 transport and they have"weeks" backlog. Looked at uhaul specs w/car ramps a @ 41" min.

Go out to measure the tire track (knowing it wouldn't fit) , pull tractor out and check it again - It showed NO signs of doing so even at low idle or off - left the lock off and came back 30 min later - nothing!!
I saw some had this issue intermittently where they theorized that some particle or contaminant gets caught in the valve and then flushes out...

WTH...is there really a ghost in the BH or just a fluke? Common sense says move on. I used it for another few hours Tuesday and all good. But, I don't want to be stupid if I should get it into the dealer now rather than sticking my head in the sand and have expensive repairs soon after. Have lots of work planned in the next several weeks before Memorial Day.

What do you all think?

Based on your narrative I am leaning towards a sticky port relief. As in you actuste the relief during the normal course of operation and it hangs open rather than closing as it should. Could be a sticky poppet or something lodging in the seat.

Dann

 

[bbxlr8]

Thanks- no difference between cold/hot when it occurred.

• Not sure what you mean by the sticky port relief - infer it is a valve/port assembly where it opens & closes to control the pressure?
• Will check the linkages asap

 

[TheOldHokie]

Thanks- no difference between cold/hot when it occurred.

• Not sure what you mean by the sticky port relief - infer it is a valve/port assembly where it opens & closes to control the pressure?
• Will check the linkages asap

Port reliefs are on the individual work ports so you dont overload the cylinders with digging forces. Not sure whats on this particular machine but the parts breakdown of the boom valve section should tell you.

Dan

 

[nbryan]

These valve consist of a valve housing, spool, load check valve, overload relief valve, etc.
I'd guess it's the load check valve for the boom lift cylinder that's misbehaving, hopefully stops doing so.

 

[TheOldHokie]

These valve consist of a valve housing, spool, load check valve, overload relief valve, etc.
I'd guess it's the load coiheck valve for the boom lift cylinder that's misbehaving, hopefully stops doing so.

Port relief not load check. Load check is blocked when spool is in neutral.

Dan

 

[nbryan]

Port relief not load check. Load check is blocked when spool is in neutral.

Dan

Ok, I'm confident you're right, so the load check does what? So there's no pressure on it at all when spool in neutral? Be nice to know more about how these work, and terminology! Load check to me intuitively meant check back pressure when cylinder under load. Obv I dunno!

 

[TheOldHokie]

Ok, I'm confident you're right, so the load check does what? So there's no pressure on it at all when spool in neutral? Be nice to know more about how these work, and terminology! Load check to me intuitively meant check back pressure when cylinder under load. Obv I dunno!

Your intuuition is right about the name but not the exact way they work. In a nutshell:

1. When a spool is shifted the first thing that happens is the center core is blocked causing the pressure in the parallel "power core" to increase. It is the power core not the center core that feeds pressurized oil to the spool. I have marked that power core path in red on the BH77 schematic you so kindly provided.
2. The load check is located in the power core pressure inlet port of each work section as I indicated in the schematic. When a spool is shifted there is an initial lag as pressure builds in the power core. If the work port that has been connected is under pressure from a raised load there is a potential for that pressure to be higher than the pressure building in the power core. That would cause a momentary reverse flow and the load can drop. The purpose of the load check is to prevent that reverse flow until the pressure in the power core rises enough to support any work port load and push the load check off its seat. The only time the load check is connected to the work port is when the inlet port is open. In neutral the load check and power core inlet is blocked by the spool.
3. The port reliefs if present are located in the load side of a work port and are conncted to the tank port. If some external force is applied to the actuator sufficient to cause a dangerous pressure spike in the work circuit they unload that presssure to tank. They are always in the circuit and if they leak for any reason the actuator can drift.

Any questions?

Dan

 

[beckmurph]

I would suggest removing the spool valves and take it to your local hydraulic shop for testing.

Three years ago they were $3700 at Kubota.

Both times I had this problem it was the spool valve.

 

[Runs With Scissors]

Common sense says.... carry on.

The only thing I'm curious about is if there's any difference in that boom sag occurrence, frequency or rate with the hydraulics cold vs hot?

Pop off the control valves cover plate and look at the cleanliness, tightness, clearances, and alignment of the control linkages now its been worked seriously for a while. Any tightness or binding resulting from loose or misaligned control linkages could cause your issue.

My BH77 valve linkages had pins loose and some binding going on, causing major sloppiness in operation. I also found the levers were actually hitting the cover plate before full valve motion, too. Left the rubber boots on but the plate off now permanently. No sagging occurrences yet that I've noticed.

100% agree with trying this first!!!

Paul

 

[TheOldHokie]

I would suggest removing the spool valves and take it to your local hydraulic shop for testing.

Three years ago they were $3700 at Kubota.

Both times I had this problem it was the spool valve.

Help me out here. The control valve is a sectional valve. Did you take the entire stack to the shop and what did they determine was wrong with the valve?

The boom work section costs $1200 and does not include the port relief cartridges

Not sure which port relief holds the boom but the low port relief cartridge is $450 and the high port relief cartridge is $720.

Failure of the relatively inexpensive port relief cartridge is a known cause of this problem and R&R is real easy. R&R of the entire stack not so much.....

Dan

 

[beckmurph]

Help me out here. The control valve is a sectional valve. Did you take the entire stack to the shop and what did they determine was wrong with the valve?

The boom work section costs $1200 and does not include the port relief cartridges

Not sure which port relief holds the boom but the low port relief cartridge is $450 and the high port relief cartridge is $720.

Failure of the relatively inexpensive port relief cartridge is a known cause of this problem and R&R is real easy. R&R of the entire stack not so much.....

Dan

I took the entire valve kit to the shop.
It was easier to let them disassemble it and not worry about leaks.

R&R the valve is not too bad.
I was proud of myself for not having
left over parts or unused hoses.

 

[bbxlr8]

Holy moly and thank you for the tutorial - I really want to understand what is going on and how it is supposed to operate.

Level-up questions:

1. Most have this problem at higher hours right?
2. What would cause this in a low-hour unit and why on earth did it not appear in 2 years of use if there was a base problem from the manufacture?

 

[TheOldHokie]

Holy moly and thank you for the tutorial - I really want to understand what is going on and how it is supposed to operate.

Level-up questions:

1. Most have this problem at higher hours right?
2. What would cause this in a low-hour unit and why on earth did it not appear in 2 years of use if there was a base problem from the manufacture?

I dont see anything that would mske me think there is s manufacturing problem.

The port relief valves are designed to cushion shocks and unload pressures that can occur in normal usage. They WILL occassionally open and close in most usage.

The frequency with which the reliefs operate is dependent on the operator and type of usage.

Oil cleanliness is also a factor

In other words its a highly variable situation with unpredictable failures.

In your case Iwould say do as others have suggested. Make sure the oil is clean and continue to use the machine in the hopes it was a one off event. If the problem reappears you can deal with it then. Its typically more a nusance problem and does not prevent you from using the machine.

Dan

 

[bbxlr8]

Super thanks Dan - suspected that but is counterintuitive based on the fact that I changed out the full case H Fluid & filter @ 50 hours JIC. Meaning it is super clean, should be flushed out from break-in etc. but you never know...