Specifications, Service and Repair of Farm and Lawn Tractors

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Kubota BX23, BX23S, BX24, BX25, BX25D hydraulic system - Adjusting and servicing

Kubota BX23, BX23S, BX24, BX25, BX25D - Mower linkage

The mower rear link and the lift arm are linked with the mower lift arm, the lift upper boss and the lift lower boss. As the hydraulic control lever moves to lift position, lift arm is raised and the lift bracket is pulled to pull the lift links to the rearward. As a result, mower rear link is lifted. The cutting height adjusting dial adjusts cutting height of mower by rotating the adjusting cam. The position of mower rear link is adjusted by changing the length of the adjusting bolt.

Adjusting mower lift linkage

Check the lift arm free play. Loosen the adjusting nut and start the engine. Move the hydraulic control lever to Lift position until the relief valve operating (Uppermost position). Adjusting bolt until the clearance between stopper and mower rear link L.H. Clearance (Kubota BX23, BX23S, BX24, BX25, BX25D) - 0 to 0.5 mm / 0 to 0.01 in. Secure the lock nut.

Disassembling mower linkage

Remove the clevis pin and remove the lift link rear L.H. Remove the pin and remove the mower rear links. Remove both side of boss and remove the lift link rear R.H. Remove the cutting height adjusting dial knob. Remove the nut and remove the adjusting cam and cutting height adjusting rod. Removing mower linkage and wire harness - Disconnect the mower linkage. Remove the wire harness clamp and wire harness from the hydraulic cylinder block.

Kubota BX23, BX23S, BX25, BX25D - Hydraulic cylinder

Checking hydraulic cylinder bore

Check the cylinder internal surface for scoring or damage. Measure the cylinder I.D. with a cylinder gauge. If the measurement exceeds the allowable limit, replace the hydraulic cylinder block. Cylinder I.D - 80.05 to 80.15 mm / 3.152 to 3.155 in. Checking hydraulic arm shaft bushing - Hydraulic arm shaft O.D. L.H - 31.925 to 31.950 mm / 1.2569 to 1.2578 in. R.H - 29.925 to 29.950 mm / 1.1782 to 1.1791 in. Visually inspect the DX bushings for signs of wear or damage. The DX bushing tends to show concentrated wear. If the DX bushing is worn beyond the alloy thickness, replace it. Hydraulic arm shaft bushing Alloy thickness - 0.57 mm / 0.022 in.

Removing hydraulic cylinder block

Remove the hydraulic hose. Remove the hydraulic cylinder block mounting bolts. Remove the hydraulic cylinder block. Hydraulic cylinder block mounting bolt - 40 to 44 Nm / 29 to 32 lbf-ft. Removing lift rod and lower link - Remove the top lin. Remove the stopper pin and remove the check chain plate. Move the bushes to inside. Move the shaft to right side and remove the lower link as a unit. Removing hydraulic piston - Inject the compressed air into the hydraulic cylinder, and remove the hydraulic piston. Apply transmission fluid to the O-ring. Replace the O-ring if it is damaged, worn or scratched, which may cause oil leakage. Removing lowering speed adjusting valve - Remove the internal snap ring and remove the lowering speed adjusting shaft. Remove the ball and spring.

Kubota BX23, BX23S, BX24, BX25, BX25D - Hydraulic pump

Checking hydraulic pump oil flow

Disconnect the power steering controller hose (inlet) from the power steering pipe. Cap the power steering pipe with plug. Remove the hydraulic pipe behind the hydraulic cylinder and fix the flow meter hose and the flow (meter) inlet. Remove the transmission fluid filling plug, then fix the flow meter hose and the flowmeter (outlet). If the flow volume is insufficient, replace the pump. Pump oil flow (Hydraulic pumpdelivery at no pressure) - 24.9 L/min. After measuring the flow volume, remove the flow meter then reassembling the hydraulic pipe to the original position.

Removing lift rod and lower link

Remove the top link. Remove the stopper pin and remove the check chain plate. Move the bushes to inside. Move the shaft to right side and remove the lower link as a unit. Removing hydraulic pump - Disconnect the mower linkage. Remove the lift arm L.H. Remove the hydraulic pipes. Remove the hydraulic pump. Since the mounting bolt is installed through the transaxle case to the transmission oil tank, seal the sealing tape to the mounting bolt securely. Hydraulic pump mounting bolt (M6) - 7.9 to 9.3 Nm / 5.8 to 6.8 lbf-ft. Hydraulic pump mounting bolt (M8) - 18 to 20 Nm / 13 to 15 lbf-ft.

Checking clearance between tip of gear tooth and casing

Measure the gear O.D. with an outside micrometer. Gear O.D (Kubota BX23, BX23S, BX24, BX25, BX25D) - 33.520 to 33.530 mm / 1.3197 to 1.3200 in. Measure the casing I.D. with a cylinder gauge and calculate the clearance. Case I.D - 33.570 to 33.577 mm / 1.3217 to 1.3219 in. If the clearance exceeds the allowable limit, replace the assembly. Clearance between tip of gear tooth and casing - Allowable limit 0.15 mm / 0.0059 in.

Checking clearance between bushing and shaft

Measure the gear shaft O.D. with an outside micrometer. Shaft O.D - 14.970 to 14.980 mm / 0.58937 to 0.58976 in. Measure the bushing I.D. with a cylinder gauge and calculate the clearance. Bushing I.D - 15.000 to 15.061 mm / 0.59056 to 0.59295 in. If the clearance exceeds the allowable limit, replace it. Clearance between bushing and shaft - 0.020 to 0.091 mm / 0.00079 to 0.0035 n. Checking side plate thickness - Measure the side plate thickness with an outside micrometer. If the thickness is less than the allowable limit, replace it. Side plate thickness - 2.48 to 2.50 mm / 0.0977 to 0.0984 in.

Kubota BX23, BX23S, BX24, BX25, BX25D - Control valve

Removing control valve

Remove the control valve. Remove the internal snap ring and draw out the spool. Removing control valve lever - Pull out the pin. Remove the control valve lever and arm. Removing lift arm, hydraulic arm shaft and hydraulic arm - Remove the external snap rings and remove the lift arms. Draw out the hydraulic arm shaft. Align the alignment marks of the hydraulic arm and hydraulic arm shaft. Align the alignment marks of the lift arms and hydraulic arm shaft. Apply grease to the right and left bushings and O-rings. Removing control valve (Front loader) - Disconnect the hydraulic hoses. Disconnect hydraulic pipes. Disconnect the rods. Remove the control valve from the valve stay. After reassembling a valve, check for oil leakage by starting up engine.

Disassembling front loader control valve

Remove the load check valve assemblies. Remove the detent plug assemblyand plug. Remove the bucket spool with parts from the valve body. Remove the boom spool with parts from the valve body. Clean all parts with a suitable solvent, and dry with a lint-free cloth or air. Visually inspect all parts for damage. When installing the spools into the valve body, be careful not to damage the O-rings.

Checking relief valve setting pressure

Disconnect the hydraulic hose from the right side of the transaxle. Install the hydraulic hose and adaptor with pressure gaug. Start the Kubota BX23, BX23S, BX24, BX25, BX25D engine and set at maximum speed. Engine speed / Oil temperature Maximum 45 to 55C / 113 to 131F. Move the control lever all way up to operate the relief valve and read the gauge. If the pressure is not within the factory specifications, adjust with the adjusting shim. Relief valve setting pressure - 12.3 to 12.7 MPa / 1780 to 1840 psi. Thickness of shim - 0.1 mm / 0.004 in. 0.2 mm / 0.008 in. 0.4 mm / 0.02 in. 0.269 MPa (39.0 psi) pressure is increased whenever the thickness of adjusting shim is increased by 0.1 mm (0.004 in.).

Function of loader control valve

The control valve assembly consists of one casting block and four major sections. The boom control valve is of 4-position, 6-connection, detent, spring center type, consisting of a mono block valve housing, spool, load check valve, etc. This valve has A1 and B1 ports and controls oil flow to the boom cylinder. The bucket control valve is of 3-position, 6-connection, no detent, spring center type, consisting of a mono block valve housing, spool, load check valve, etc. This valve has A2 and B2 ports and controls oil flow to the bucket cylinder. The P port is connected to the outlet port of hydraulic block by the hydraulic pipe. The T port is connected to the tank port of hydraulic block by the hydraulic pipe. Power beyond (PB port) - This section has PB port which is connected to the inlet port of hydraulic block by the hydraulic hose, and feeds oil to the three point hydraulic control valve.

Loader control lever in neutral position - When the loader control lever is set at neutral position, the hydraulic oil enters from P port (P), flows through the boom spool valve and the bucket spool valve, and exits at PB port (PB).

Loader control lever in up position - When the loader control lever is set at up position, the boom spool valve moves outward. This creates an oil passage between the boom spool valve and the front loader control valve. The pressured oil from the pump port (P) enters to this oil passage. The pressured oil is delivered to the boom cylinder through 1B port (1B). This extends and raises the boom cylinder. When the boom spool valve moves outward, a passage between the boom spool valve and 1A port (1A) is created. The return oil from the boom cylinder enters 1A port (1A), flows through the bucket spool valve and exits to PB port (PB).

Loader control lever in down position - When the loader control lever is set at down position, the boom spool valve moves inward. This creates an oil passage between the boom spool valve and the front loader control valve. The pressured oil from the pump port (P) enters to the newly opened passage. The pressured oil is delivered to the boom cylinder through 1A port (1A). This retracts and lowers the boom cylinder. When the boom spool valve moves inward, a passage between the boom spool valve and 1B port (1B) is created. The return oil in the boom cylinder enters 1B port (1B), flows to the bucket spool valve, and exits to the PB port (PB).

Loader control lever in floating position (Kubota BX23, BX23S, BX24, BX25, BX25D) - When the loader control lever is set to floating position, the boom spool valve moves further inward. This creates oil passages at 1A port (1A) and 1B port (1B), as well as a passage between the boom spool valve and the front loader control valve. The low pressured oil from the pump port (P) flows through the bucket spool valve, and exits to the PB port. The low pressured return oil in the boom cylinder enters 1A port (1A), flows through the boom spool valve, andgoes to the tank port (T). The other low pressured return oil in the boom cylinder enters 1B port (1B), flows through the boom spool valve, and goes to the tank port (T). As a result, the boom is floating.

Loader control lever in roll-back position - When the loader control lever is set at roll-back position, the bucket spool valve moves outward. This creates oil passages at 2A port (2A) and 2B port (2B). The pressured oil from the pump port (P) flows through 2B port (2B) to the bucket cylinder. The low pressured return oil from the bucket cylinder enters 2A port (2A), flows through the front loader control valve, and goes to the tank port (T). As a result, the bucket moves to roll-back position.

Loader control lever in dump position - When the loader control lever is set to the dump position, the bucket spool valve moves to the right. This creates an oil passage at 2A port (2A). The passage between 2B port (2B) and T port (T) is also opened. The pressure-fed oil from P port (P) flows to the neutral passage through the boom control section. As the passage to the PB port (PB) is closed by the bucket spool valve, the arriving oil opens the load check valve and flows to 2A port (2A) through the notched section of the bucket spool valve. This extends the bucket cylinder. Return oil from the bucket cylinder enters 2B port (2B) and travels throughout the valve to go to the transmission case through T port (T).

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