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Kubota D902 Engine body - Disassembling and assembling

Kubota D902 - Cylinder head and valves

Kubota D902 engines are mainly used for BX23, BX24, BX25D, BX2370, BX2380, BX2230, BX2350, BX2360 tractors.

Cylinder block

The cylinder block is the main housing of engine and supports the other main parts. The cylinder block is usually of integrated cast iron construction, and includes complete passages for coolant and lubricating oil. Closed breather - Closed breather system has been adopted to prevent the release of blow-by gas into the atmosphere. After its oil content is filtered by oil shield, the blow by gas in fed back to the intake manifold through breather valve to be used for re-combustion. Half-floating head cover - The half-floating head cover helps reduce noise coming from the cylinder head. Rubber packing is fitted in to keep the cylinder head cover 0.5 mm (0.02 in.) or so off the cylinder head. Removing cylinder head cover - Disconnect the breather hose. Remove the cylinder head cover nuts. Remove the cylinder head cover. Check to see if the cylinder head cover gasket is not damaged.

Removing cylinder head and cylinder head gasket

Loosen the pipe clamps, and remove the water return pipe. Remove the cylinder head screw in the order of (n) to (a) and remove the cylinder head. Remove the cylinder head gasket. Do not use O-ring on the pin pipe. It is not necessary to retighten the cylinder head screw and to readjust valve clearance after engine warmed up. Replace the cylinder head gasket with a new one. When mounting the gasket, set it to the pin pipe holes. Be careful not to mount it reversely. The cylinder head should be free of scratches and dust. Install the cylinder head, using care not to damage the gasket. After applying engine oil to the thread of screws, tighten them in several steps and specified sequence (a) to (n). Cylinder head screw (Kubota D902 engine for BX2370, BX2380, BX2230, BX2350, BX2360, BX23, BX23S, BX24, BX25, BX25D tractors) - 38 to 42Nm / 28 to 31 lbf-ft. Removing tappets - Remove the tappets from the crankcase. Visually check the contact between tappets and cams for proper rotation. If problem is found, replace tappets. Before installing the tappets, apply engine oil thinly around them.

Removing valves

Remove the valve caps. Remove the valve spring collet, pushing the valve spring retainer by valve spring replacer. Remove the valve spring retainer, valve spring and valve stem seal. Remove the valve. Wash the valve stem and valve guide hole, and apply engine oil sufficiently. After installing the valve spring collets, lightly tap the stem to assure proper fit with a plastic hammer.

Kubota D902 - Piston and connecting rod

Piston

The piston creates the forces for the suction, compression, power and exhaust cycles. The reciprocating motion of a piston in the engine cylinder creates the forces for the suction, compression, power and exhaust cycles. The piston's skirt is coated with molybdenum disulfide which reduces the piston slap noise and thus the entire operating noise. The molybdenum disulfide improves the fit of the piston with the cylinder and helps to prevent scorching. This material helps resist metal wears even with little lube oil.

Piston ring

Piston rings are classified as compression and oil control rings. Diesel engine has two or three compression rings around the piston head and one oil ring just below them. The compression rings prevent gases from leaking by the piston during the compression and expansion strokes. They seal by expanding out against the cylinder wall. The rings expand by their own tension and also by combustion pressure behind the rings during the expansion stroke. The compression rings are split for easy assembly on the piston.

The piston rings are usually made of hardened cast iron. To reduce the wear on the ring, they are often plated with chrome on their contact faces, or are coated their contact faces with molybdenum disulfide. The top compression ring is a keystone type ring to get durability against heavy load. The second compression ring is an undercut ring to prevent shortage of oil. The main job of the oil control ring is to wipe the excess oil from the cylinder walls. This oil is fed through slots in the rings to holes in the piston groove, where it returns to the crankcase. For better oil control, spring expanders are often used under the oil control ring.

Connecting rod and crankshaft

The connecting rod connects the piston to the crankshaft. The connecting rod must be light and yet strong enough to transmit the thrust of the piston to crankshaft. The big end of connecting rod has a crankpin bushing (split type) and the small end has a small end bushing (solid type). The crankshaft converts the up-and-down motion of the pistons into rotary motion. It ties together the reactions of all the pistons into one rotary force that drives the machine. The crankshaft is made of tough special alloy steel, and the journals, pins and oil seal sliding portions are induction hardened to increase the hardness for higher wear resistance. The front journal is supported by a split type and the intermediate journal by a split type, and the rear journal by a split type with thrust bearings. The crankshaft is provided with an oil gallery, through which engine oil is fed to the crankpin portion, and lubricates it.

Removing connecting rod

Remove the connecting rod cap. Align the marks (a) with each other. (Face the marks toward the injection pump). Apply engine oil to the connecting rod screws and lightly screw it in by hand, then tighten it to the specified torque. If the connecting rod screw does not screw in smoothly, clean the threads. If the connecting rod screw is still hard to screw in, replace it. Connecting rod screw (Kubota D902 engine for BX2370, BX2380, BX2230, BX2350, BX2360, BX23, BX23S, BX24, BX25, BX25D tractors) - 27 to 30 Nm / 20 to 22 lbf-ft. Removing pistons - Turn the flywheel and bring the piston to top dead center. Draw out the piston upward by lightly tapping it from the bottom of the crankcase with the grip of a hammer.

Draw out the other piston in the same method as above. Do not change the combination of cylinder and piston. Make sure of the position of each piston by marking. For example, mark “1” on the No. 1 piston. When installing the piston into the cylinder, place the gaps of all the piston rings as shown in the figure. Carefully insert the pistons using a piston ring compressor. Otherwise, their chrome-plated section may be scratched, causing trouble inside the cylinder. Before inserting the piston into the cylinder, apply enough engine oil to the piston. When inserting the piston into the cylinder, face the mark on the connecting rod to the injection pump.

Removing piston ring and connecting rod

Remove the piston rings using a piston ring tool. Remove the piston pin, and separate the connecting rod from the piston. Mark the same number on the connecting rod and the piston so as not to change the combination. Install the rings so that the manufacturer's mark near the gap faces the top of the piston. When installing the oil ring onto the piston, place the expander joint on the opposite side of the oil ring gap. Apply engine oil to the piston pin. When installing the connecting rod to the piston, immerse the piston in oil and insert the piston pin to the piston. Temperature of oil For 10 to 15 minutes - 80C (176F). When installing the connecting rod to the piston, align the mark on the connecting rod to the fanshaped concave.

Kubota D902 - Rocker arm and Camshaft

Camshaft

The camshaft controls the opening and closing of the intake and exhaust valves in the cylinder head. The camshaft is normally driven by gearing from the crankshaft. This is made of special cast iron, and the journal and cam sections are chilled to resist wear. One intake and one exhaust cam is provided for each cylinder. The journal diameters are large to permit removal of the shaft from its bore. The journal sections are force lubricated.

Rocker arm

The rocker arm is an oscillating lever that conveys radial movement from the camshaft lobes into linear movement at the exhaust and intake valves to open and close them. The rocker arms are mounted on a rocker arm shaft (a single hollow shaft) at the top of the engine. When the push rods move up, the mating rocker arm is moved down, contacting its valve stem tip and opening the valve. Lubricating oil pressurized through the rocker arm bracket to the rocker arm shaft, which serves as a fulcrum so that the rocker arm and the entire system are lubricated sufficiently.

Removing rocker arm and push rod

Remove the rocker arm bracket screw. Remove the rocker arm assembly. Remove the push rods. After installing the rocker arm, be sure to adjust the valve clearance. When refitting the push rods into the tappets, make sure the push rod locates correctly into the tappet seat. Rocker arm bracket screw (Kubota D902 engine for BX2370, BX2380, BX2230, BX2350, BX2360, BX23, BX23S, BX24, BX25, BX25D tractors) - 9.81 to 11.2 Nm / 7.24 to 8.31 lbf-ft.

Kubota D902 - Flywheel

Flywheel

A flywheel is a rotating mechanical device that is used to store rotational energy. The flywheel is generally made of heavy cast iron or steel and has gear teeth around its outer rim, which mesh with the drive pinion of starter. The flywheel stores the rotating force in the combustion stroke as inertial energy, reduces crankshaft rotating speed fluctuation and keeps the smooth rotating conditions. The flywheel periphery is inscribed with the marks showing fuel injection timing angle lines and top dead center mark TC. The flywheel mounted on the rear of the crankshaft is a stabilizer for the whole engine.

Removing flywheel

Secure the flywheel to keep it from turning, using a flywheel stopper. Remove all flywheel screws and then remove the flywheel. Align the “1TC” mark (a) on the outer surface of the flywheel horizontally with the alignment mark (b) on the rear end plate. Now fit the flywheel in position. Apply engine oil to the threads and the undercut surface of the flywheel screw and fit the screw. Flywheel screw - 54 to 58 Nm / 40 to 43 lbf-ft. Removing bearing case cover - Remove the bearing case cover mounting screws. Remove the bearing case cover. Fit the bearing case gasket and the bearing case cover gasket with correct directions. Install the bearing case cover to position the casting mark “UP” on it upward. Apply engine oil to the oil seal lip and be careful that it is not rolled when installing. Tighten the bearing case cover mounting screws with even force on the diagonal line. Bearing case cover mounting screw - 9.81 to 11.2 Nm / 7.24 to 8.31 lbf-ft.

Removing main bearing case assembly

Remove the two main bearing case screws 1 of each main bearing cases. Remove the main bearing case from crankshaft. Clean the oil passage in the main bearing cases. Apply clean engine oil on the bearings. Install the main bearing case assemblies in the original positions. Since diameters of main bearing cases vary, install them in order of markings from the gear case side. Match the alignment numbers (a) on the main bearing case assembly. When installing the main bearing case , face the mark “FLYWHEEL” to the flywheel. Install the thrust bearing with its oil groove facing outward. Make sure that the main bearing case moves smoothly after tightening the main bearing case screw to the specified torque. Main bearing case screw - 13 to 15 Nm / 9.4 to 11 lbf-ft.

Kubota D902 - Timing gears

Timing gears

The timing gears correctly control fuel injection to the cylinders and valve timing. The timing gears transmit torque from the crankshaft to the oil pump and injection pump and, at the same time, correctly control fuel injection to the cylinders and valve timing. Each gear has a mating mark inscribed on it for correct and easy assembly and is spherical with teeth set obliquely to the axis of rotation to rotate smoothly and reduce noise. The crankshaft is the hub around which other parts of the engine can be timed and driven. This is done by the meshing of gears.

Removing gear case

Remove the fuel feed pump. Remove the gear case. Grease thinly to the oil seal, and install it, ensuring the lip does not come off. Removing speed control plate - Remove the engine stop solenoid. Remove the speed control plate. Be careful not to drop the governor spring into the crankcase.

Removing cam gear, idle gear 1, 2 and governor gear

Remove the idle gear 1. Remove the fuel camshaft stopper. Draw out the fuel cam gear with fuel camshaft. Remove the camshaft stopper bolt. Remove the cam gearwith camshaft. Remove the external snap ring from the governor shaft. Remove the governor gear with governor shaft. Three-lever type fork lever To remove the governor shaft, follow the procedures in 5, 6 above and never remove fork lever and the max. torque limiter. When installing the idle gear, be sure to align the alignment marks on each gears. Apply engine oil thinly to the fuel camshaft before installation. Make sure to assemble the external snap ring of the governor shaft. Check the governor shaft for smooth rotation.