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Kubota D902 - Fuel system

Kubota D902 Fuel system - Function and Components

Fuel from the fuel tank passes through the fuel filter, and then enters the injection pump after impurities such as dirt, water, etc. are removed. The fuel pressurized by the injection pump to the opening pressure (13.7 to 14.7 MPa, 140 to 150 kgf/cm2, 1990 to 2133 psi), of the injection nozzle is injected into the combustion chamber. Part of the fuel fed to the injection nozzle lubricates the moving parts of the needle valve inside the nozzle, then returns to the fuel tank through the fuel overflow pipe from the upper part of the nozzle holder. Function of fuel filter (Kubota D902 engine for BX2370, BX2380, BX2230, BX2350, BX2360, BX23, BX23S, BX24, BX25, BX25D tractors) - The fuel filter filters impurities from the fuel. In-line filter is installed in the fuel line with an electromagnetic fuel feed pump and is used to filter impurities such as dirt, water, etc.

Fuel feed pump

An electromagnetic fuel feed pump is used when a fuel tank is set below the pump of the engine. An electromagnetic fuel feed pump uses a transistor that causes the pump to start pumping fuel when the main switch is turned to the ON position. Therefore, fuel is supplied to the injection pump regardless of engine speed. This pump is driven by the battery. It can therefore be operated even with the engine being stopped.

Injection nozzle

Uses as E-TVCS system, the small-sized DENSO made OPD mini nozzle is of a flat-cut-provided double throttle type. This type of nozzle is designed to control the injection quantity when the lift rate is low at start of the injection, and to cut down on the knocking sound caused by excessive fuel injection by giving the needle valve section more taper than before to prevent the rapid increase in the injection quantity when the initial injection turns into the full-force injection. Also, employed to prevent the injection quantity loss in the throttle section caused by carbon, the flat cut provided at the needle valve section helps the throttle withstand long use and reduce as much knocking sound as when it was new. The heat seal is employed to improve the durability and reliability of the nozzle.

Kubota D902 Fuel system - Checking and adjusting

Checking injection timing

The liquid gasket is not required for assembling. Shims are available in thickness of 0.20 mm (0.0079 in.), 0.25 mm (0.0098 in.), 0.30 mm (0.012 in.) and 0.175 mm (0.00689 in.). Combine these shims for adjustments. Addition or reduction of shim (0.05 mm, 0.002 in.) delays or advances the injection timing by approx. 0.009 rad (0.5 deg). In disassembling and replacing the injection pump, be sure to use the same number of new shims with the same thickness. The 0.175 mm thick shim is coated only on the lower face. Therefore, do not use the 0.175 mm thick shim as the top shim of the combination (injection pump side), because this can cause oil leakage.

Remove the injection pipes

Remove the engine stop solenoid. Turn the flywheel counterclockwise (viewed from flywheel side) until the fuel fills up to the hole of the delivery valve holder for No. 1 cylinder. After the fuel fills up to the hole of the delivery valve holder for No. 1 cylinder, turn back (clockwise) the flywheel around 1.6 rad (90 deg). Turn the flywheel counterclockwise to set at around 0.44 rad (25 deg) before T.D.C. Slowly turn the flywheel counterclockwise and stop turning when the fuel begins to come up, to get the present injection timing. Check to see the degree on flywheel. The flywheel has mark “1TC”, “10” and “20” for the crank angle before the top dead center of No. 1 cylinder. If injection timing is out of adjustment, readjust the timing with shims. Injection timing (Kubota D902 engine for BX2370, BX2380, BX2230, BX2350, BX2360, BX23, BX23S, BX24, BX25, BX25D tractors) - 0.3360 to 0.3621 rad (19.25 to 20.75 deg) before T.D.C.

Checking fuel tightness of pump element

Remove the engine stop solenoid. Remove the injection pipes and glow plugs. Install the injection pump pressure tester to the injection pump. Install the injection nozzle jetted with the proper injection pressure to the injection pump pressure tester. Set the speed control lever to the maximum speed position. Run the starter to increase the pressure. If the pressure cannot reach the allowable limit, replace the pump with new one. Fuel tightness of pump element Allowable limit - 13.73 MPa / 1991 psi.

Checking fuel tightness of delivery valve

Remove the engine stop solenoid. Remove the injection pipes and glow plugs. Set a pressure tester to the fuel injection pump. Install the injection nozzle jetted with the proper injection pressure to the injection pump pressure tester. Run the starter to increase the pressure. Stop the starter when the fuel jets from the injection nozzle. After that, turn the flywheel by the hand and raise the pressure. Now turn the flywheel back about half a turn (to keep the plunger free). Keep the flywheel at this position and clock the time taken for the pressure to drop. Measure the time needed to decrease the pressure. If the measurement is less than allowable limit, replace the pump with new one. Fuel tightness of delivery valve 10 seconds - 13.73-12.75 MPa / 1991-1849 psi. Checking nozzle spraying condition - Set the injection nozzle to a nozzle tester, and check the nozzle spraying condition. If the spraying condition is damaged, replace the nozzle piece.

Checking fuel injection pressure

Pressure variation difference of adjusting washer thickness. Set the injection nozzle to a nozzle tester. Slowly move the tester handle to measure the pressure at which fuel begins jetting out from the nozzle. If the measurement is not within the factory specifications, replace the adjusting washer in the nozzle holder to adjust it. Fuel injection pressure (Kubota D902 engine for BX2370, BX2380, BX2230, BX2350, BX2360, BX23, BX23S, BX24, BX25, BX25D tractors) - 13.73 to 14.70 MPa / 1992 to 2133 psi.

Checking valve seat tightness

Set the injection nozzle to a nozzle tester. Raise the fuel pressure, and keep at specified pressure for 10 seconds. Valve seat tightness (No fuel leak at) - 12.75 MPa / 1849 psi. If any fuel leak is found, replace the nozzle piece.

Checking nozzle holder

Secure the nozzle retaining nut with a vise. Remove the nozzle holder, and remove parts inside. Assemble the nozzle in clean fuel oil. Install the push rod, noting its direction. After assembling the nozzle, be sure to adjust the fuel injection pressure. Tightening torque: Nozzle holder - 35 to 39 Nm / 26 to 28 lbf-ft, Overflow pipe retaining nut - 20 to 24 Nm / 15 to 18 lbf-ft, Nozzle holder assembly - 49 to 68 Nm / 37 to 50 lbf-ft.

Kubota D902 Fuel system - Removing and Installation

Removing injection pump

Disconnect the start spring on the thrust lever side. Align the control rack pin with the notch on the crankcase, and remove the injection pump. Remove the injection pump shims. In principle, the injection pump should not be disassembled. Addition or reduction of shim delays or advances the injection timing. In disassembling and replacing, be sure to use the same number or new gasket shims with the same thickness. When installing the injection pump, insert the control rack pin firmly into the groove of the thrust lever of fork lever.

Removing injection pipes

Loosen the screws to the pipe clamp. Remove the injection pipes. Send compressed air into the pipes to blow out dust. Then, reassemble the pipes in the reverse order. Injection pipe retaining nut - 25 to 34 Nm / 18 to 25 lbf-ft.

Removing nozzle holder assembly and glow plug

Remove the overflow pipe. Remove the nozzle holder assemblies. Remove the copper gasket and heat seal. Remove the lead from the glow plugs. Remove the glow plugs. Replace the copper gasket and heat seal with new ones. Overflow pipe retaining nut - 20 to 24 Nm / 15 to 18 lbf-ft. Nozzle holder assembly - 49 to 68 Nm / 37 to 50 lbf-ft. Glow plug - 7.9 to 14 Nm / 5.8 to 10 lbf-ft.

Removing nozzle heat seal

Use a plus (phillips head) screw driver that has a diameter which is bigger than the heat seal hole. Drive screw driver lightly into the heat seal hole. Turn screw driver three or four times each way. While turning the screw driver, slowly pull the heat seal out together with the injection nozzle gasket. If the heat seal drops, repeat the above procedure. Heat seal and injection nozzle gasket must be changed when the injection nozzle is removed for cleaning or for service. Disconnecting fuel hoses - Disconnect fuel return hose and fuel supply hose from engine. Disconnect fuel filter from engine.