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Disassembly and assembly the Orbitrol steering unit 160/125 cm3

- Remove the steering unit from the Massey Ferguson 6460, 6499, 6497 Tractor.

- Place the steering unit in a vice fitted with plastic jaws.

- Take out the screws (1). Carefully mark the location of the screw (2) and then remove it.

- Remove the cover plate (4), O'ring (5), stator (6) and O'ring (8).

- Remove the spacer (10), the rotor (9), the distributor plate (29) and the O'ring (28).

- Take out the splined link shaft (11).

Fig.33. Parts list

(23) Suction valves (24) Bush (25) Spool valve (26) Non-return valve (27) Sleeve (28) O’ring (29) Distributor plate (1) Screw (2) Screw (3) Seal (4) Closing plate (5) O’ring (6) Stator (7) Cotter pin (8) O’ring (9) Rotor (10) Spacer (11) Link shaft (12) Washer (13) Centring springs (14) Needle bearing (15) Bush (16) Washer (17) O’ring (18) Relief valve (19) Seal (20) Shock valve (21) Orbitrol steering unit (22) Non-return valve

- Unscrew the threaded bush and recover the ball from the non-return valve (22).

- Take out the two axle pins and the balls from the suction valves (23) of the Massey Ferguson 6460, 6499, 6497 Tractors steering unit.

- Extract the sleeve (27) and spool valve (25) assembly by pushing it out while checking that the pin (7) lies along the horizontal axis.

- Remove the washers (12) (16), the needle bearing (14) and the bush (24) from the sleeve and spool valve assembly. Remove the pin (7), and the centring springs (13) by pressing on their ends. Separate the sleeve (27) from the spool valve (25).

- Unscrew the plug from the relief valve (18). Using an 8 mm Allen wrench, disassemble the threaded bush and remove the seal, the spring and the valve (the crimped seat cannot be removed).

- Unscrew the two plugs from the shock valves (20) and remove the seals. Using a 6 mm Allen wrench, remove the threaded bushes and take out the springs and valve balls from their seats (the crimped seats cannot be removed).

- Extract the seal (19), the bush (15) and the O'ring (17).

- Disassemble the non-return valve (26).

- Check and clean all components. Replace any defective parts. Lubricate the components with clean transmission oil.

- Reassemble the non-return valve (26).

- Install the seal (19), the O'ring (17) and the ring (15).

- Place the valve balls and springs in the recesses of the shock valve (20). Screw in the threaded bushes, fit the seals and tighten the plugs.

- Install the valve and spring in the recesses of the relief-valve (18), screw in the threaded bush. Fit the seal and tighten the plug to a torque of 40 - 60 Nm.

- Insert the MF 6460, 6499, 6497 Tractor spool valve (25) into the sleeve (27). Position the centring springs (13) and insert the pin (7).

- Position the bush (24) on the sleeve and spool valve assembly so that the chamfer facilitates assembly in the steering unit.

- Place the washers (12) (16), the chamfer of washer (12) towards the centring springs (13), by inserting the needle bearing (14) between them.

- Install the sleeve and spool valve assembly in the steering unit by oscillating it slightly. Check that the pin (7) is held horizontally.

- Install the two valve balls and the two pins in the recesses of the suction valves (23).

- Install the valve ball in the recess of the non-return valve (22) and screw in the threaded bush. Position the splined link shaft (11).

- Install the O'ring (28) and the distributor plate (29).

- Install the rotor (9) so that the two concave depressions C lie along the axis of the slot in the splined link shaft (11). Refit the spacer (10).

- Place the O'rings (5 )(8) on the stator (6).

- Align the stator (6) fitting holes with those of the Massey Ferguson MF 6499, 6497, 6460 Tractor steering unit. Refit the stator on the steering unit without moving the rotor (9). Install the cover plate (4).

- Install the screw (2) (in the same location as marked during disassembly) and the screws (1) fitted with their seals (3). Tighten opposing screws to a torque of 30 - 35 Nm.

- Using a test-bench or a suitable fixture, check the adjustment and correct operation of the steering unit.

- Install the steering unit on the tractor. Check the oil tightness of the hydraulic unions.

Manual steering (engine stopped)

When the pump is no longer operating or the available pressure is too low the rotor is no longer hydraulically driven. It is no longer power assisted. In this case, action on the steering wheel compresses the centring springs.

The angular clearance between the pin and the sleeve is reduced to zero resulting in mechanical rotation of stator and rotor.

The MF 6460, 6499, 6497 Tractor steering unit then operates in the same way as a hand pump. The oil arriving from steering ram passes through the non-return valve and supplies the metering device.

The pressure generated is proportional to the torque applied to the steering wheel. A great effort is therefore required to turn the wheel in order to steer the tractor.

Fig.34. Legend

A - Double acting steering ram, BP - Priority block(s), L - LH hydraulic port of the steering ram, LS - Signal, P - Pressure, R - RH hydraulic port of the steering ram, T - Return.