Specifications, Service and Repair of Farm and Lawn Tractors

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Kubota D902 - Lubricating system

Kubota D902 Lubricating system - Function and Components

Lubricating system (Kubota D902 engine for BX2370, BX2380, BX2230, BX2350, BX2360, BX23, BX23S, BX24, BX25, BX25D tractors) consists of oil strainer, oil pump, relief valve, oil filter cartridge and oil pressure switch. The oil pump sucks lubricating oil from the oil pan through the oil strainer and the oil flows down to the filter cartridge, where it is further filtered. Then the oil is forced to crankshaft, connecting rods, idle gear, camshaft and rocker arm shaft to lubricate each part. Some part of oil, splashed by the crankshaft or leaking and dropping from gaps of each part, lubricates these parts: piston, cylinders, small ends or connecting rods, tappets, push rods, inlet and exhaust valves and timing gears.

Function of oil strainer - The oil strainer strains large particles from the oil. The strainer has a mesh screen suitable for straining large particles from the oil and yet passes a sufficient quantity of oil to the inlet side of the oil pump. The strainer is located so all oil entering the pump from the oil pan must flow through it.

Function of oil pump - The oil pump circulates engine oil under pressure to the rotating bearings, the pistons and the camshaft. The oil pump sucks lubricating oil from the oil pan through the oil strainer and the oil flows down to the oil filter. The rotor pump is driven from the crankshaft. This oil pump has an inner rotor and an outer rotor. The inner rotor, which is driven by crankshaft, rotates the outer rotor in the same direction. The inner rotor has one less lobe than the outer rotor, and they are eccentrically engaged with each other.

Function of oil filter - The oil filter is responsible for filtering impurities from the oil. In the filtration system, there is only one oil flow from the oil pump to the oil filter cartridge. After filtering, the oil goes to the lubricating portion, and is returned to the crankcase. When the filter cartridge is new, there is very little pressure drop through the filter element. However, if the filter gets clogged, the resulting pressure (the oil pressure in inlet line builds up by 98 kPa (1.0 kgf/cm2, 14 psi) more than the outlet line) will open the bypass valve and allow unfiltered oil to bypass to the lubricating portion.

Relief valve - The relief valve prevents the damage of the lubricating system due to high oil pressure. The valve is closed when the spring tension is greater than the oil pressure at the inlet. The spring tension holds poppet securely in position. The valve opens when the oil pressure at the inlet exceeds that of the spring. This pushes the poppet off the inlet hole and oil flows through the valve.

Oil pressure switch - The oil pressure switch activates the oil warning light when the oil pressure falls below specified value. The oil pressure switch is mounted on the cylinder block and is led to the lubricating oil passage. When the oil pressure falls below the specified value, the oil pressure-warning lamp lights. At the proper oil pressure - When the engine is started and as the proper oil pressure builds, the diaphragm is pushed up. This separates the contact rivet and breaks the circuit, causing the lamp to go out. At lower oil pressure - If the oil pressure drops, the resulting deflection of the diaphragm will close the contact rivet and again complete the circuit. The lighted lamp warns that the pressure of the lubricating system has dropped below the pressure setting.

Kubota D902 Lubricating system - Checking and servicing

Checking engine oil pressure

Remove the engine oil pressure switch, and set an oil pressure tester. Start the engine. After warming up, measure the oil pressure of both idling and rated speeds. If the oil pressure is less than the allowable limit, check the following. Engine oil insufficient. Oil pump damaged. Oil strainer clogged. Oil filter cartridge clogged. Oil gallery clogged. Excessive oil clearance. Foreign matter in the relief valve. Relief valve spring length. D902 engine oil pressure (Kubota BX2370, BX2380, BX2230, BX2350, BX2360, BX23, BX23S, BX24, BX25, BX25D tractors). At idle speed More than - 49 kPa / 14 psi. At rated speed -- 197 to 441 kPa / 28.5 to 64.0 psi. Allowable limit - 147 kPa / 21.3 psi. After checking the engine oil pressure, tighten the engine oil pressure switch to the specified torque. Oil pressure switch - 15 to 19 Nm / 11 to 14 lb-fft.

Oil pump Checking

Checking rotor lobe clearance - Measure the clearance between lobes of the inner rotor and the outer rotor with a thickness gauge. If the clearance exceeds the factory specifications, replace the oil pump rotor assembly. Rotor lobe clearance - 0.030 to 0.14 mm / 0.0012 to 0.0055 in. Checking clearance between outer rotor and pump body - Measure the clearance between the outer rotor and the pump body with a thickness gauge. If the clearance exceeds the factory specifications, replace the oil pump rotor assembly. Clearance between outer rotor and pump body - 0.070 to 0.15 mm / 0.0028 to 0.0059 in. Checking clearance between rotor and cover - Put a strip of plastigauge onto the rotor face with grease. Install the cover and tighten the screws. Remove the cover carefully, and measure the amount of the flattening with the scale and get the clearance. If the clearance exceeds the factory specifications, replace oil pump rotor assembly. Clearance between rotor and cover - 0.0750 to 0.135 mm / 0.00296 to 0.00531 in.

Checking relief valve

Remove the oil filter base. Check the relief valve for dirt, and the seat and ball for damage. If damaged, replace. Check the free length of spring. If less than the allowable limit, replace. Relief valve spring (Kubota D902 engine for BX2370, BX2380, BX2230, BX2350, BX2360, BX23, BX23S, BX24, BX25, BX25D tractors) - 32 mm / 1.26 in. Tightening torque - 40 to 49 Nm / 29 to 36 lbf-ft.

Kubota D902 Lubricating system - Removing and install

Removing oil pan and oil strainer

Remove the oil pan mounting screws. Remove the oil pan. Remove the oil strainer. Scrape off the old adhesive completely. Wipe the sealing surface clean using waste cloth soaked with gasoline. Now apply new adhesive thick all over the contact surface. Apply the adhesive also on the center of the flange as well as on the inner wall of each screw hole. New adhesive Apply Thickness - 3.0 to 5.0 mm (0.12 to 0.19 in.). Cut the nozzle of the "liquid gasket" container at its second notch. Apply "liquid gasket" about 5.0 mm (0.19 in.) thick. Within 20 minutes after the application of fluid sealant, reassemble the components. Wait then for about 30 minutes, and pour oil in the crankcase. Liquid gasket Apply Thickness - 5.0 mm / 0.19 in. After cleaning the oil strainer, check to see that the filter mesh in clean, and install it. Visually check the O-ring, apply engine oil, and install it. Securely fit the O-ring to the oil strainer. To avoid uneven tightening, tighten oil pan mounting screws in diagonal order from the center.

Draining engine oil

Start and warm up the engine for approx. 5 minutes. Place an oil pan underneath the engine. Remove the drain plug to drain oil. After draining, reinstall the drain plug. Never mix two different type of oil. Use the proper SAE Engine Oil according to ambient temperature. Fill the engine with the new engine oil through the oil inlet to the upper line on the dipstick (3). Engine oil Capacity - 3.1 L. Tightening torque: Drain plug with copper gasket (M12, 1.25) - 33 to 37 Nm / 24 to 27 lbf-ft.

Separating Kubota 902 engine

The rear engine mounting nuts secure ground cables to the L.H. and R.H. engine supports. If the rear engine mounting nuts have already been removed from a previous step, just remove the front engine mounting nuts. Securely attach the lifting chain to the engine hooks. Remove the L.H. and R.H. engine supports (4). Cushion mounting nut - 24 to 27 Nm / 18 to 20 lbf-ft. Engine support mounting screw - 48 to 55 Nm / 36 to 41 lbf-ft.

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