Specifications, Service and Repair of Farm and Lawn Tractors

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Kubota D902 - Cooling system

Kubota D902 - Cooling system components

The cooling system cools the engine while it operates to prevent overheating and keep a proper operating temperature. Kubota D902 engines for BX2370, BX2380, BX2230, BX2350, BX2360, BX23, BX23S, BX24, BX25, BX25D tractors are used pressurized forced-circulation type. This system consists of a radiator, water pump, cooling fan, thermostat and coolant temperature sensor (some models). The coolant is cooled through the radiator core, and the fan set behind the radiator pulls cooling air through the core to improve cooling.

When the coolant in the engine is at a low temperature, the thermostat valve is closed so that the coolant is circulated in the engine through the bypass pipe. When the temperature of the coolant becomes the valve opening temperature of thermostat, the thermostat opens the valve to return the heated coolant to the radiator. The water pump sucks the cooled coolant, forces it into the cylinder block and draws out the hot coolant. Some engines employ the bottom bypass system to improve the cooling performance of radiator and the three step valve opening type thermostat to reduce thermal shock radically.

Water pump - The water pump circulates the coolant through the system. If the pump fails to circulate the coolant, heat is not removed from the engine and overheating damage may occur. Kubota engines use a centrifugal type, and is driven by the crankshaft via a fan belt. It is compose of a pump body, impeller, mechanical seal and bearing unit.

Function of radiator - The radiator is one of the major components of coolant cooling system. The radiator is one of the major components of coolant cooling system. It is here that heat in the coolant is released to the atmosphere. The radiator core consists of water carrying tubes and fins at a right angle to the tubes. Kubota D902 engine (BX2370, BX2380, BX2230, BX2350, BX2360, BX23, BX23S, BX24, BX25, BX25D tractors) use corrugated fin type core which has a right weight and high heat transfer rate. Radiators are usually made of copper or brass. Recently, however, aluminum-made radiators are introduced for their light weight.

Radiator cap - The radiator cap keeps coolant from boiling out or evaporating. The pressure system permits operating the engine at a higher temperature without boiling the coolant or losing it by evaporation. The radiator cap consists of a pressure valve, vacuum valve, valve springs, gasket, and has two functions. Pressure valve open - The pressure valve in the cap permits the escape of coolant or steam when the pressure reaches a certain point (88 kPa, 0.90 kgf/cm2, 13 psi). Vacuum valve open - The vacuum valve in the cap opens to prevent a vacuum in the cooling system.

Kubota D902 Cooling system - Checking and adjusting

Checking fan belt tension

Measure the deflection, depressing the belt halfway between the fan drive pulley and alternator pulley at specified force. If the measurement is not within the factory specifications, loosen the alternator mounting screws and relocate the alternator to adjust. Depressing fan belt Specified force - 98 N / 22 lbf. Deflection - 7.0 to 9.0 mm / 0.28 to 0.35 in.

Checking fan belt damage and wear

Check the fan belt for damage. If the fan belt is damaged, replace it. Check if the fan belt is worn and sunk in the pulley groove. If the fan belt is nearly worn out and deeply sunk in the pulley groove, replace it. Checking radiator cap air leakage - Set a radiator tester and an adapter on the radiator cap. Apply the specified pressure. Specified pressure - 88 kPa / 13 psi. If the measurement is less than the factory specification, replace the radiator cap.

Checking radiator water leakage

The pressure of the leak test is different from each radiator specification. Thus, do the leak test referring to the test pressure of each radiator specification. Pour a specified amount of water into the radiator. Set a radiator tester and an adaptor and raise the water pressure to the specified pressure. Check the radiator for water leaks. For water leak from the pinhole, repair with the radiator cement. When water leak is excessive, replace the radiator.

Checking thermostat valve opening temperature

Suspend the thermostat in the water by a string with its end inserted between the valve and seat. Heating the water gradually, read the temperature when the valve opens and leaves the string. Continue heating and read the temperature when the valve opens. If the measurement is not within the factory specifications, replace the thermostat. Thermostat's valve opening temperature (Kubota D902 engine for BX2370, BX2380, BX2230, BX2350, BX2360, BX23, BX23S, BX24, BX25, BX25D tractors) - 69.5 to 72.5C / 157.1 to 162.5F. Temperature at which thermostat completely opens - 85C / 185F.

Kubota D902 Cooling system components, removing and installing

Removing thermostat assembly

Remove the thermostat cover mounting screws, and remove the thermostat cover. Remove the thermostat assembly. Apply a liquid gasket (Three Bond 1215 or equivalent) only at the thermostat cover side of the gasket.

Removing fan drive pulley

Secure the flywheel to keep it from turning. Remove the fan drive pulley screw. Draw out the fan drive pulley with a puller. Install the pulley to crankshaft, aligning the mark on them (D902 engine). Apply engine oil to the fan drive pulley retaining screw. And tighten it. Fan drive pulley screw - 118 to 127 Nm / 86.8 to 94.0 lbf-ft.

Draining coolant and removing outer engine parts

Connect the engine stands to the crankcase. Open the radiator drain plug, and remove radiator cap to completely drain the coolant. After all coolant is drained, close the drain plug. Loosen the inlet hose band and the radiator hose bands, and remove the radiator with the radiator hoses and the air cleaner. Loosen the fan belt. Remove the alternator, the starter motor, the fan and the fan belt. Remove the heat proof cover, the muffler and the exhaust manifold. Tank Capacity - 2.7 L.

Separating 902 engine

Removing battery - Remove the under panel. Disconnect the negative cable from the battery. Disconnect the positive cable from the battery and remove the battery. Removing bonnet - Remove the front guard. Open the bonnet. Disconnect the headlight harness from the headlights and bonnet. Disconnect the bonnet guide rod from the bonnet. Disconnect the L.H. and R.H. bonnet brackets from the frame. Remove the bonnet.

Disconnecting wiring harness and ground cables - Disconnect the starter connector and cable, oil pressure switch, alternator connector and cable and coolant temperature switch. Disconnect the stop solenoid and glow plug wire. Disconnect the ground cables. Tightening torque: Engine mounting nut - 24 to 27 Nm / 18 to 20 lbf-ft. Disconnecting accelerator wire - Disconnect accelerator wire from speed control lever. Disconnecting propeller shaft assembly - Disconnect the propeller shaft assembly from the propeller spacer. Tightening torque: Propeller shaft assembly bolt - 24 to 27 Nm / 18 to 20 lbf-ft.

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