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Kubota B21, BX2680, B2301, B7500 Engine - Checking and Adjusting

Kubota D1005 Three-cylinder diesel engine used in B21, BX2680, B2301, B7500 tractors.

Kubota B21, BX2680, B2301, B7500 - Engine Components

Cylinder Block

Kubota D1005 engine has a high durability tunnel-type cylinder block in which the crank bearing component is a constructed body. Furthermore, liner less type, allow effective cooling, less distortion, and greater wear-resistance. The noise level is reduced to a minimum because each cylinder has its own chamber.

Crankshaft

The crankshaft with the connecting rod converts the reciprocating motion of the piston into the rotating motion. 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 solid type bearing, 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 lubricate it.

Rocker Arm

The rocker arm assembly includes the rocker arms, rocker arm brackets and rocker arm shaft and converts the reciprocating movement of the push rods to an open/close movement of the inlet and exhaust valves. Lubricating oil is pressurized through the bracket to the rocker arm shaft, which serves as a fulcrum so that the rocker arm and the entire system are lubricated sufficiently.

Kubota B21, BX2680, B2301, B7500 - Flywheel

The flywheel is connected with the crankshaft, it stores the rotating force in the combustion stroke as inertial energy to rotate the crankshaft smoothly. The flywheel periphery is provided with marks showing fuel injection timing and top dead center. The flywheel and crankshaft can be fixed to each other at a certain point according to the arrangement of flywheel mounting screw hole. On the circum ference of the flywheel are stamped the top dead center (1TC) mark for the 1st cylinder and four lines indicating every 0.087 rad. (5°) of crank angle from 0.175 rad. (10°) to 0.436 rad. (25°) before mark 1TC.

Air Cleaner

The air cleaner is of a dry type with evacuator valve for easy maintenance. The dust, while circulating in the air flow, is absorbed by the element and thus prevented from entering the engine. The dust, while circulating in the air flow, is absorbed by the element and thus prevented from entering the engine.

Muffler

The muffler consists of an inner tube with a series of holes and outer tube. The exhaust noises are absorbed and dumped, while the gas pass through a series of holes on the inner tube.

Cylinder Head and Valves

Valve recessing - 0.4 mm. Clearance between Valve Stem and valve guide - 0.1 mm. Valve guide - 7.010 to 7.025 mm. Valve guide protrusion - 10 mm. Valve seat width - 2.12 mm (0.0835 in.). Clearance between rocker arm shaft and rocker arm - 0.10 mm. Rocker arm shaft - 11.973 to 11984 mm. Push rod alignment - 0.25 mm.

Timing Gears and Camshaft

Crank gear/Idle gear - 0.032 to 0.115 mm. Idle gear/Cam gear - 0.036 to 0.114 mm. Idle gear/Injection pump gear 0.034 to 0.116 mm. Injection pump gear/Governor gear 0.033 to 0.117 mm. Clearance between the idle gear and the idle gear collar with a dial gauge - 0.9 mm. Clearance between the cam gear and the camshaft stopper - 0.30 mm. Oil clearance of camshaft - 0.050 to 0.091 mm. Camshaft bearing journal O.D. - 35.934 to 35.950 mm. Camshaft bearing I.D. - 36.000 to 36.025 mm. Clearance between idle gear shaft and idle gear bushings - 0.020 to 0.054 mm. Idle gear shaft O.D. - 25.959 to 25.975 mm.

Piston and Connecting Rod

Clearance between piston pin and small end bushing - 0.014 to 0.038 mm. Small end bushing - 22.025 to 22.040 mm. Top ring - 0.25 to 0.40 mm. Second ring - 1.25. Oil ring - 0.020 to 0.055 mm.

Crankshaft

Oil clearance between crankpin and crankpin bearing - 0.029 to 0.091 mm. Oil clearance between crankshaft journal and cranks aft bearing 1 - 0.034 to 0.114 mm. Oil clearance between crankshaft journal and cranks aft bearing 2 - 0.034 to 0.095 mm. Flywheel sway - 0.05 mm. Crankshaft side clearance - 0.15 to 0.31 mm.

Cylinder

In general, maximum wear appears at direction of point which is about 20 mm (0.787 in.) from the top edge while minimum wear is at direction of point. Wear of cylinder I.D. - 72.000 to 72.019 mm. Bore and finish the cylinder inner wall using a hone to a diameter + 0.5 mm (0.0197 in.) larger than the standard. The surface roughness after honing must be 1.2 to 2.0. Oversized cylinder - 72.500 to 72.519 mm.

Kubota B21, BX2680, B2301, B7500 - Lubrication System

Oil Pump

The oil pump in Kubota D1005 engine is a trochoid pump. Inside the pump body, the 10 lobe inner rotor is eccentrically engaged with the 11 lobe outer rotor. The inner rotor is driven by the crankshaft, which in turn rotate the outer rotor. When the inner rotor rotates, the outer rotor also rotates in the same direction. The two rotors have differences in lobe number and center, which generates space between lobes. At position, there is little space between lobes in the inlet port. As the rotor rotates towards position, the space between the lobes becomes larger, creating a negative pressure which sucks in oil. Outside the inlet port, the space between the lobes becomes gradually smaller, and oil pressure increases. At position, oil is discharged from the outlet port.

Rotor Lobe Clearance

Measure the clearance between lobes of the inner rotor and the outer rotor with a feeler gauge. If the clearance exceeds the factory specification, replace the oil pump rotor assembly. Outer and inner rotor clearance - 0.06 to 0.18 mm.

Clearance between Outer Rotor and Pump Body

Measure the clearance between the outer rotor and the pump body with a feeler gauge. If the clearance exceeds the factory specification, replace the oil pump rotor assembly. Radial clearance between outer rotor and pump body - 0.10 to 0.18 mm.

Clearance between Rotor and Cover

Put a strip of press gauge onto the rotor face with grease. Install the cover and tighten the screws. Remove the cover carefully, and measure the width of the press gauge with a sheet of gauge. If the clearance exceeds the factory specification, replace oil pump rotor assembly. End clearance between rotor and cover - 0.025 to 0.75 mm.

Relief Valve

The relief valve prevents the damage of the lubricating system due to high oil pressure. This relief valve is a ball type direct acting relief valve, and is best suited for low pressures. When oil pressure exceeds the upper limit, the ball is pushed back by the pressure oil and the oil escapes.

Kubota B21, BX2680, B2301, B7500 - Cooling System

The cooling system consists of a radiator, centrifugal water pump, suction fan and thermostat. The water is cooled through the radiator core, and the fan set behind the radiator pulls cooling air through the core to improve cooling. The water pump sucks the cooled water, forces it into the cylinder block and draws out the hot water. Then the cooling is repeated. Furthermore, to control temperature of water, a thermostat is provided in the system. When the thermostat opens, the water moves directly to radiator, but when it closes, the water moves toward the water pump through the bypass between thermostat and water pump. The opening temperature of thermostat is approx. 82C (180F).

Radiator

The radiator core consists of water carrying tubes and fins at a right angle to the tubes. Heat of hot water in the tubes is radiated from the tube walls and fins. KUBOTA's engine uses corrugated fin type core which has a ligl1t weight and high heat transfer rate. Clogging is minimized by the louver less corrugated fins.

Radiator Cap

The radiator cap is for sustaining the internal pressure of the cooling system at the specified level 88 kPa (0.9 kgf/cm2, 13 psi) when the engine is in operation. The cap consists of a pressure valve a vacuum valve, valve springs, gasket, etc. Cooling water is pressurized by thermal expansion of steam, and as its boiling temperature rises, generation of air bubbles will be suppressed. (Air bubbles in cooling water lowers the cooling effect).

Fan Belt Tension

Press the fan belt between fan drive pulley and dynamo pulley (or alternator pulley) at 98N (10 kgf, 221bs) of force. If the deflection is not within the factory specifications, loosen the bolts, and relocate the dynamo (or alternator) to adjust. If the belt is damaged or worn, replace the belt.

Thermostat's Valve Opening Temperature

Push down the thermostat valve and insert a string between the valve and the valve seat. Place the thermostat and a thermometer in a container with water and gradually heat the water. Hold the string to suspend the thermostat in the water. When the water temperature rises, the thermostat valve will open, allowing it to fall down from the string. Read the temperature at this moment on the thermometer. Continue heating the water and read the temperature when the valve has risen by about 6mm (0.236 in.). If the measurement is not acceptable, replace the thermostat.

Radiator Water Leakage

Pour a specified amount of water into the radiator. Set a radiator tester. Increase water pressure to the specified pressure. Check each section for water leakage. When water leakage is excessive, replace the radiator. If water leakage is caused by a small pinhole, correct the radiator with radiator cement.

Radiator Cap Air Leakage

Set a radiator tester to the radiator cap. Apply the specified pressure of 98.1 kPa (0.9 kgf/cm2, 12.8 psi). Check if the pressure drop to less than 59 kPa (0.6 kgf/cm2, 9 psi) in 10 seconds. If the pressure is less than the factory specification, replace it.

Kubota B21, BX2680, B2301, B7500 - Fuel System

Injection Pump

A Bosch MD type mini pump is used for the injection pump. It is small, lightweight and easy to handle. The plunger with a left-hand lead reciprocates via the tappet roller by means of the camshaft fuel cam, causing the fuel to be delivered into the injection nozzle. No fuel delivery - At the engine stop position of the control rack, the lengthwise slot on the plunger aligns with the feed hole. And the delivery chamber is led to the feed hole during the entire stroke of the plunger. The pressure in the delivery chamber does not build up and no fuel can be forced to the injection nozzle. Fuel delivery - The plunger is rotated by the control rack. When the plunger is pushed up, the hole is closed. The pressure in the delivery chamber builds up and force-feeds the fuel to the injection nozzle until the control groove meets the feed hole. The amount of the fuel corresponds to the distance. The pump element is consist of the plunger and cylinder. The sliding surfaces are super-precision machined to maintain injection pressure at engine low speeds. Since the driving face fits in the control sleeve, the plunger is rotated by the movement of the control rack to increase or decrease of fuel delivery. As described above, the plunger is machined to have the slot and the control groove.

The delivery valve consists of the delivery valve and delivery valve seat. The delivery valve performs the following functions. Reverse flow preventing function - If the fuel flow reverse from the injection nozzle side when the plunger lowers, the time lag between the next delivery start and the nozzle injection start increases. To avoid this, the delivery chamber to injection pipe interruption by delivery valve prevents this reverse flow, thus keeping fuel always filled in the nozzle and pipe. Suck-back function - After completing the fuel delivery, the delivery valve lowers, and the relief plunger end contacts the delivery valve seat. The valve further lowers until its seat surface seats firmly the delivery valve seat. During this time, the amount of fuel corresponding to is sucked back from inside the injection pipe, the pressure inside the pipe is reduced, thus leading to an improved injection shut off and preventing after leakage dribbling.

Dumping Valve: At fuel injection - Since dumping valve is pushed up to press the spring, fuel is pressure-fed to injection nozzle the same as without dumping valve. At suck-back - At suck-back by delivery valve after fuel injection fuel returns through dumping valve orifice. Generally second injection is apt to occur by reflex pressure due to reaction of sudden pressure drop when changing into suck-back by delivery valve from high injection pressure. As a result of preventing this second injection perfectly by dumping valve and dissolving nozzle clogging, durability of injection nozzle is improved.

Injection Nozzle

This nozzle is of 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 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 with stand 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. The injection pressure is 13.73 to 14.71 MPa (140 to 150 kgf/cm2, 1991 to 2133 psi), and is adjusted with adjusting washers.

Kubota B21, BX2680, B2301, B7500 - Injection Timing

When inspecting the fuel injection timing, the timing control actuates during starting and the correct fuel injection timing cannot be measured. Remove the injection pipes. Remove the engine stop solenoid, push in the control rack of the injection pump by 5 mm (0.2 in.) and hold it at that position. Turn the flywheel counterclockwise until fuel flows from the delivery valve holder. Continue to turn the flywheel slowly, and stop it as soon as the fuel level at the tip of the delivery valve holder begins to increase. Check to see if the timing angle lines on the flywheel is aligned with the alignment mark. If the timing is out of adjustment, readjust the timing with shims.

Fuel Tightness of Pump Element

Remove the injection pipes and glow plugs, and install the pressure tester. With the speed control lever at the full injection position, turn the crankshaft counterclockwise (facing the flywheel). If the pressure does not build up to the fuel injection pressure, replace the delivery valve with new one and test again. If the pressure does not built up more than the fuel injection pressure, replace the injection pump assembly. After replacing only pump element, the amount of injection should be adjusted on a specified test bench.

Fuel Tightness of Delivery Valve

The delivery valve is checked in the same way as the pump element. Turn the flywheel counterclockwise to make the pressure gauge indicate 14.7 MPa (150 kgf/cm2, 2133 psi). Set the mark on the flywheel of the cylinder being checked to the position at 90° clockwise from the punch mark on the rear end plate (This lowers the pressure inside the delivery chamber). If it takes the pressure five seconds or more to drop from 14.7 MPa (150 kgf/cm2, 2133 psi) to 13.7 MPa (140 kgf/cm2, 1991 psi) the delivery valve can be used. If the measured value stays below the allowable limit, replace the pump assembly or the delivery valve.

Nozzle Injection Pressure

Set the injection nozzle to the 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, disassemble the injection nozzle, and change adjusting washer until the proper injection pressure is obtained. Pressure variation with 0.025 mm (0.00098 in.) difference of adjusting washer thickness. Approx. 588 kPa (6 kgf/cm 2, 85 psi).

Nozzle Spraying Condition

Set the injection nozzle to a nozzle tester and check the nozzle spraying condition. If the spraying condition is defective, replace the nozzle piece.

Fuel Tightness of Needle Valve Seat

Set the injection nozzle to a nozzle tester. Apply a pressure 12.75 MPa (130kgf/cm2, 1849 psi). After keeping the nozzle under this pressure for 10 seconds, check to see if fuel leaks from the nozzle. If fuel should leak, replace the nozzle piece.

Kubota B21, BX2680, B2301, B7500 - Engine Separating

Draining Cooling Water

Loosen the drain cock from the radiator hose to drain cooling water. Remove the radiator cap to drain cooling water completely.

Draining Engine Oil

Start and warm up Kubota D1005 engine for approx. 5 minutes. Place an oil pan underneath the engine. Remove the drain plug to drain oil. Screw in the drain plug. Fill the engine oil up to the upper line on the dipstick.

Drain the Transmission Oil

Place oil pans underneath the transmission case. Remove the four drain plugs at the bottom of the transmission case. Drain the transmission oil. After draining, screw in the four drain plugs. Fill new oil from filling port after removing the filling plug up to the upper notch on the dipstick. After running the engine for few minutes, stop it and check the oil level again, if low, add oil prescribed level. Transmission oil capacity: Manual transmission - 11 L, HST transmission - 12 L.

Hood and Side Cover

Open the hood from front and remove the spling lock pin and remove the food with hood rod for keeping it open. Remove the front grille. Remove the right and left side cover. Disconnect the battery cords.

Radiator Hoses, Muffler Pipe and Hydraulic Pipes

Loosen the clamps and disconnect radiator hoses. Remove the muffler pipe. Disconnect the radiator stay and then dismount the radiator. Dismount the battery. Loosen the clamps of hydraulic hoses and remove the battery stay with oil cooler then remove the delivery pipe (from HST) and return pipe (from oil cooler) (HST type).

Fuel Hoses and Fuel Filter

Close the fuel filter cock. Disconnect the fuel hose between fuel pump and fuel filter at the fuel filter side. Remove the fuel filter mounting screw and remove the fuel filter from the bracket.

Propeller Shaft Cover and Coupling

Loosen the clamp and slide the propeller shaft cover to the rear. Tap out the spring pin and then slide the coupling to the rear.

Drag Link

Steer the front wheels to the left. Remove the slotted nut and disconnect the drag link from the knuckle arm.

Steering Wheel

Remove the steering wheel cap. Remove the steering wheel mounting nut and remove the steering wheel with a steering wheel puller.

Meter Pedal and Panel Under Cover

Remove the meter panel and disconnect the meter panel connector and hour-meter cable from the meter panel. Then remove the meter panel. Tap out the spring pin and remove the hand accelerator lever. Disconnect the combination switch connector and main switch connector. Remove the panel under cover mounting screw, and take off the panel under cover.

Kubota B21, BX2680, B2301, B7500 - Fuel Tank

Remove the fuel tank frame stay. Disconnect the regulator and hazard unit connectors and remove the lead wire for fuel gauge. Remove the fuse box. Disconnect the overflow hoses of fuel line. Remove the tank flame with fuel tank.

Universal Joint and Bearing Holder

Loosen the clamp and slide the universal joint cover to the rear. Tap out the spring pins and then slide the universal joint to the rear. Remove the bearing holder and universal joint. Make sure the yokes of universal joints must always be in the same plane as shown in the figure. Apply grease to the splines of the propeller shaft and universal joint. When inserting the spring pins, face their splits in the direction parallel to the universal joint.

Suction Pipe, Delivery Pipe and Power Steering Pipes and Others

Remove the foot accelerator rod. Remove the power steering delivery pipe. Remove the power steering return pipe (HST Type). Loosen the joint bolt of delivery pipe on the hydraulic cylinder and disconnect the flare nut of 3-point hitch delivery pipe. Remove the fuel filter bracket. Loosen the cramp of suction hose and remove the suction hose from the hydraulic pump. Remove the shutter plate.

Separating the Engine from Clutch Housing

Remove the wiring harness. Place the jack under the center frame. Hoist the engine by the chain at the engine hook. Remove the engine mounting screws and separate the engine from the clutch housing.