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Kubota BX24, BX25, BX25D - BT601 backhoe

Kubota BX24, BX25, BX25D - BT601 backhoe Hydraulic Valve

Inlet - This section has P and T ports. The P port is connected to the OUTLET port of Kubota BX24, BX25, BX25D tractor connected by the quick coupler. The T port is connected to the transaxle case by the quick coupler. Control Valve Section - The control valves are of 3 positions, 6 connections, no detent, spring center type. These valves have A and B ports and control oil flow to each cylinders. These are consisting of a valve housing, spool, load check valve, overload relief valve, etc.

Outlet Section - This section has P.B. port which is connected to the INLET port of hydraulic block or front loader control valve. Pressure-fed oil from the hydraulic pumps are delivered into P port in the inlet section. As the load check valves are kept closed in the neutral position. oil flows along the notched section of the spools to the P.B port through the neutral passage. Then the oil is fed to the front loader valve or transaxle case and pipe from the P.B port.

Bucket (Roll-back) - When the dipperstick and bucket lever is moved to the left to set to the "ROLL-BACK" position, the spool of the bucket control valve moves to the right. which forms oil passage between bridge passage and B1 port, and between A1 port and T port. The pressure-fed oil from the P port opens the load check valve and flows to B1 port to extend the bucket cylinder. Return oil from the bucket cylinder returns to the transmission case through the A 1 port. low pressure passage and T port.

Bucket (Dump) - When the dipperstick and bucket lever is moved to the right to set to the "DUMP" position, the spool of the bucket control valve moves to the left, which forms oil passage between bridge passage and Ai port, and between B1 port and T port. The pressure-fed oil from the P port opens the load check valve and flows to A1 port to retract the bucket cylinder. Return oil from the bucket cylinder returns to the transmission case through the B1 port, low pressure passage and T port.

Boom (Up) - When the boom and swing lever is pulled to the backward to set to the "UP" position, the spool of the boom control valve moves to the left, which forms oil passage between bridge passage and B5 port, and between A5 port and T port. The pressure-fed oil from the P port opens the load check valve and flows to B5 port to retract the boom cylinder. Return oil from the boom cylinder returns to the transmission case through the AS port, low pressure passage and T port.

Boom (Down) - When the boom and swing lever is pulled to the forward to set to the "DOWN" position, the spool of the boom control valve moves to the right, which forms oil passage between bridge passage and AS port, and between B5 port and T port. The pressure-fed oil from the P port opens the load check valve and flows to AS port to extend the boom cylinder. Return oil from the boom cylinder returns to the transmission case through the B5 port, low pressure passage and T port.

Kubota BX24, BX25, BX25D - BT601 backhoe Overload Relief Valve

Overload relief valve in this control valve is a combination valve combining a relief operation and anticavitation operation. Relief Operation - When the control valve is in the neutral position, both cylinder ports of control valve are blocked by the spool. If an external load is imposed on the cylinder, pressure builds in the circuit. When the pressure exceeds the set level of the overload relief vale, the relief valve opens and the oil returns to tank. In this way, the hydraulic circuit and actuator are protected from excessive pressures.

Anti-cavitation Operation - Overload relief valve also has anti-void function. If a negative pressure takes place in the circuit, the oil is fed from the tank to eliminate the negative pressure. When the actuator port pressure is lower than the setting - The cylinder port HP is applied to the seat B in the following route: first through the throttle a of the piston poppet (1) built in the relief valve poppet, second through the spring chamber A, and then through the circular clearance between the adjusting screw and the piston poppet. This cylinder port HP works to open the pilot poppet. Because the piston spring has not reached the set pressure, however, the valve stays shut. In this way the seat remains intact and the relief valve poppet stays shut.

Kubota BX24, BX25, BX25D - Mounting Pin and Mounting BT601 Backhoe

Make sure both hoses are firmly connected before starting the engine. Start the engine. Stand beside the rear wheel. Move the boom to fully raising position and raise Kubota BT601 backhoe by operating the stabilizers until the mount bar on the backhoe main frame are slightly higher than the tractor main frame support hooks. If the support hooks are not parallel to the mount bars, adjust with the stabilizers. Move Kubota BX24, BX25, BX25D tractor backward until the support hooks on the tractor main frame are just beneath the mount bar on the backhoe main frame. Lower the mount bar onto the support hooks by operating the stabilizer and boom control levers.

Move the boom slowly to the lowering position, and engage the guide plates of the main frame to the bosses of sub frame. Then raise the rear wheels slightly by operating the boom to the lowering direction. Shut off the engine. Reinstall the mounting pins, and insert the slide bar of the mounting pins to the hole of the main frame. Be careful not to catch the hydraulic hoses between backhoe frame and tractor while mounting the backhoe. Move Kubota BX24, BX25, BX25D tractor loader backhoe to an open area and cycle all backhoe functions. This will check their operation and flow oil back through the system, filtering it and refilling each circuit. Check the hydraulic oil level before putting the backhoe into full operation.

Disassembling Kubota BT601 backhoe

Bucket - Remove the bucket from the dipper stick.

Dipperstick and Bucket Cylinder - Bucket, dipperstick, boom, swing, and stabilizer cylinder consists of cylinder head, piston rod, cylinder tube, piston and other parts. They are single-rod double acting cylinders in which the reciprocating motion of the piston is controlled by hydraulic force applied to both of its ends. Remove the pins and remove the bucket link and guide link. Disconnect the hydraulic hoses and remove the bucket cylinder. Remove the pins and remove the dipperstick. To prevent from the damage of hydraulic hoses, set the wooden block etc. between dipperstick cylinder and boom. Lock the locking nuts to setting bolts at position where the setting bolt may still be rotated. Replace the spacers at their original position.

Dipperstick Cylinder, Boom, Boom Cylinder and Hoses - Disconnect the hydraulic hoses and remove the dipperstick cylinder. Remove the pins and remove the boom cylinder. Remove the pin and remove the boom. Remove the hydraulic hoses from the control valve. Lock the locking nuts to setting bolts at position where the mounting bolt may still be rotated. Connect the hydraulic hoses at their original positions and be sure to connect the hose angle as indicated table below.

Swing Frame - Disconnect the swing cylinder rods from swing frame. Remove the swing frame from main frame. Lock the locking nuts to setting bolts at position where the setting bolt may still be rotated. Reinstall the thrust washers at their original positions.

Swing Cylinder - Remove the swing cylinder bottom pin. Disconnect the hydraulic hoses. Remove the swing cylinder.

Stabilizers and Stabilizer Cylinder - Remove the pins and remove the stabilizer cylinder with hydraulic hoses. Remove the pin and remove the stabilizer. Lock the locking nuts to setting bolts at position where the setting bolt may still be rotated.

Lever Support and Valve - Remove the cover. Disconnect the control lever rods of valve side. Remove the lever support with control levers. Disconnect the hydraulic hoses. Remove the control valve. Connect the hydraulic hoses at their original portions and be sure to connect the hose angle as indicated table below.

Backhoe Main Frame and Hydraulic Hose - Hoist the backhoe main frame and remove the mount pins. Remove the three hydraulic hoses. Separate the main frame from Kubota BX24, BX25, BX25D tractor frame.

Kubota BT601 backhoe - Servicing specifications (Clearance)

Boom Cylinder Rod Pin to Cylinder Bushing - 0.060 to 0.185 mm / 0.002 to 0.007 in.
Boom Support, Oipperstick Fulcrum Pin to Bushing - 0.140 to 0.180 mm / 0.006 to 0.007 in.
Oipperstick Cylinder Rod Pin to Cylinder Bushing - 0.060 to 0.185 mm / 0.002 to 0.007 in.
Bucket Fulcrum Pin, Bucket Cylinder Pin, Bucket Guide Link Pin to Bushing - 0.204 to 0.315 mm.
Boom Fulcrum Pin to Swing Frame Bushing - 0.140 to 0.180 mm / 0.006 to 0.007 in.
Main Frame Fulcrum Pin to Bushing - 0.070 to 0.130 mm / 0.003 to 0.005 in.
Swing Cylinder Rod Pin to Cylinder Bushing - 0.108 to 0.259 mm / 0.004 to 0.010 in.

Kubota BT601 backhoe troubleshooting

All functions inoperative (Front loader is OK) - Quick coupler disconnected.

All functions including front loader, are inoperative - Insufficient transmission fluid. Relief valve spring damaged. Hydraulic pump malfunctioning. Oil filter clogged.

Hydraulic oil overheats - Continuous operation against relief. Transmission fluid improper brand and viscosity. Relief valve mis-adjusted. Insufficient transmission fluid. Oil filter clogged.

Individual cylinder circuit weak or inoperative (Others OK) - Valve spool not moving fully. Valve spool stick (especially when warm). Overload relief valve mis-adjusted. Piston seal ring worn or damaged. Cylinder tube worn or damaged. Oil leaks from joint. Hydraulic hose damaged. Dust in overload relief valve.

Excessive cylinder movement - Piston seal ring worn or damage. Excessive valve spool to bore tolerance. Hydraulic hose or fitting damaged. Hydraulic hose or fitting loose. Cylinder tube worn or damaged.

Insufficient cylinder speed - Engine rpm too low. Hydraulic pump malfunctioning. Relief valve pressure too low. Insufficient transmission fluid.