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Kubota BX2350, BX2370, BX2380 Engine - Service and Checking

Kubota BX2350, BX2370, BX2380 tractors are equipped with a D902 three-cylinder diesel engine.

Kubota BX2350, BX2370, BX2380 - Fuel System

Injection Timing

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 1.57 rad (90°). Turn the flywheel counterclockwise to set at around 0.44 rad (25°) 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. Check to see if the timing angle on the flywheel is aligned with the alignment mark. If injection timing is out of adjustment, readjust the timing with shims. Injection timing - 0.33 to 0.37 rad (19 to 21°) before T.D.C.

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.

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 hands and raise the pressure to approx. 13.73 MPa (140 kgf/cm2, 1991 psi). Now turn the flywheel back about half a turn (to keep the plunger free). Maintain the flywheel at this position and clock the time taken for the pressure to drop from 13.73 to 12.75 MPa (from 140 to 130 kgf/cm2, from 1991 to 1849 psi). Measure the time needed to decrease the pressure from 13.73 to 12.75 MPa (140 to 130 kgf/cm2, 1991 to 1849 psi).

Kubota BX2350, BX2370, BX2380 - Fuel Injection Pressure

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. Pressure variation with 0.025 mm (0.0010 in.) difference of adjusting washer thickness. Approx. 588 kPa (6.0 kgf/cm2, 85 psi).

Cleaning Fuel Filter (Element Type only)

Close the fuel cock. Unscrew the retaining ring and remove the filter cup, and rinse the inside with kerosene. Take out the element and dip it in the kerosene to rinse. After cleaning, reassemble the fuel filter, keeping out dust and dirt. Bleed the fuel system. If dust and dirt enter the fuel, the fuel injection pump and injection nozzle will wear quickly. To prevent this, be sure to clean the fuel filter cup periodically.

Replacing Fuel Filter Cartridge (Cartridge Type)

Water and dust in fuel are collected in the filter cartridge. So, change the filter cartridge every 400 hours service. Remove the used filter cartridge with filter wrench. Apply a thin film of fuel to the surface of new filter cartridge gasket before screwing on. Then tighten enough by hand. Loosen the air vent plug to let the air out. Start Kubota D902 engine and check for fuel leakage.

Replacing Fuel Filter Element (Element Type)

Close the fuel cock. Unscrew the retaining ring and remove the filter cup, and rinse the inside with kerosene. Replace the filter element. Reassemble the fuel filter, keeping out dust and dirt. Bleed the fuel system.

Checking Injection Pump

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 can not reach the allowable limit, replace the pump with new one or repair.

Kubota BX2350, BX2370, BX2380 - Electrical System

Battery Voltage

Stop Kubota D902 engine. Measure the voltage with a circuit tester between the battery terminals. If the battery voltage is less than the factory specification, check the battery specific gravity and recharge the battery.

Magnetic Switch Test

Disconnect the battery negative cable from the battery. Disconnect the battery positive cable from the battery. Disconnect the leads from the starter B terminal. Remove the starter from the engine. Connect a jumper lead from the starter S terminal to the battery positive terminal. Connect a jumper lead momentarily between the starter’s body and the battery negative terminal. If the pinion gear does not pop out, the magnetic switch is failure. Repair or replace the starter.

Alternator on Unit Test

Before alternator on unit test, check the battery terminal connections, circuit connection, fan belt tension, charging indicator lamp, fuses on the circuit, and abnormal noise from the alternator. Prepare full charged battery for the test. Start the engine. When the engine is operating measure the voltage between two battery terminals. If the voltage is between 13.8 V and 14.8 V, the alternator is operating normally.

Engine Stop Solenoid Test (Energize to Run Type)

Disconnect the 3P connector from the engine stop solenoid wiring harness. Remove the engine stop solenoid from the engine. Connect the jumper leads from the pulling coil terminal to the switch, and from switch to the battery positive terminal. Connect the jumper leads from the holding coil terminal to the switch, and from switch to the battery positive terminal. Connect the jumper leads from the ground terminal to the battery negative terminal. When the switch is turn on, the plunger pull into the solenoid body and then the plunger comes out within approximately 1.2 seconds. Turn on the switch then turn on the switch, the plunger pull into the solenoid body and it keeps in holding position after turn off the switch. If the plunger is not attracted, the engine stop solenoid is faulty.

Replacing Battery

Disconnect the negative terminal and positive terminal. Remove the battery holder. Remove the used battery. Replace the new battery. Tighten the battery holder. Connect the positive terminal. Connect the negative terminal.

Kubota BX2350, BX2370, BX2380 - Basic Engine Parts

Compression Pressure

Run Kubota D902 engine until it is warmed up. Stop the engine. Remove the air cleaner, the muffler and all injection nozzles. Set a compression tester with the adaptor to the nozzle hole. After making sure that the stop lever is set at the stop position (non-injection), run the engine with the starter and measure the compression pressure. Repeat steps 4 and 5 for each cylinder. If the measurement is below the allowable limit, apply a small amount of oil to the cylinder wall through the glow plug hole (or nozzle hole) and measure the compression pressure again. If the compression pressure is still less than the allowable limit, check the top clearance, valve clearance and cylinder head. If the compression pressure increases after applying oil, check the cylinder wall and piston rings. Check the compression pressure with the specified valve clearance.

Checking Valve Clearance

Valve clearance must be checked and adjusted when engine is cold. Remove the cylinder head cover and the glow plugs. Align the 1TC mark on the flywheel and alignment mark on the rear end plate so that the No. 1 piston comes to the compression top dead center. Check the following valve clearance marked using a feeler gauge. If the clearance is not within the factory specifications, adjust with the adjusting screw. Then turn the flywheel 6.28 rad (360°), and align the 1TC mark on the flywheel and alignment mark on the rear end plate so that the No. 1 piston comes to the overlap position. Check the following valve clearance marked using a feeler gauge. If the clearance is not within the factory specifications, adjust with the adjusting screw. Intake and exhaust valve clearance (cold) - 0.145 to 0.185 mm / 0.00571 to 0.00728 in.

Cylinder Head and Valves

Top Clearance - Remove the cylinder head (Do not attempt to remove the cylinder head gasket). Move the piston up and stick a strip of fuse 1.5 mm dia. (0.059 in. dia.), 5 to 7 mm long (0.197 to 0.276 in. long) on the piston head at three positions with grease so as to avoid the intake and exhaust valves and the combustion chamber ports. Lower the piston, and install the cylinder head and tighten the cylinder head screws to the specified torque. Turn the flywheel until the piston exceeds top dead center. Remove the cylinder head, and measure the thickness of the squeezed fuses. If the measurement is not within the factory specifications, check the oil clearance between the crankpin and crankpin bearing and between the piston pin and small end bushing. Top clearance - 0.50 to 0.70 mm / 0.0197 to 0.0276 in.

Cylinder Head Surface Flatness

Clean the cylinder head surface. Place a straightedge on the cylinder head’s four sides and two diagonal. Measure the clearance with a thickness gauge. If the measurement exceeds the allowable limit, correct it with a surface grinder. Do not place the straightedge on the combustion chamber. Be sure to check the valve recessing after correcting. Cylinder head surface flatness - Allowable limit 0.05 mm / 0.0020 in.

Cylinder Head Flaw

Prepare an air spray red check. Clean the surface of the cylinder head with detergent. Spray the cylinder head surface with the red permeative liquid. Leave it five to ten minutes after spraying. Wash away the read permeative liquid on the cylinder head surface with the detergent. Spray the cylinder head surface with white developer. If flawed, it can be identified as red marks.

Kubota BX2350, BX2370, BX2380 - Valve Recessing

Clean the cylinder head surface, valve face and valve seat. Insert the valve into the valve guide. Measure the valve recessing with a depth gauge. If the measurement exceeds the allowable limit, replace the valve. If it still exceeds the allowable limit after replacing the valve, replace the cylinder head. Valve recessing (Intake and exhaust) - 0.10 (protrusion) to 0.10 (recessing) mm / 0.0039 (protrusion) to 0.0039 (recessing) in.

Clearance between Valve Stem and Valve Guide

Remove carbon from the valve guide section. Measure the valve stem O.D. with an outside micrometer. Measure the valve guide I.D. with a small hole gauge, and calculate the clearance. If the clearance exceeds the allowable limit, replace the valves. If it still exceeds the allowable limit, replace the valve guide. Clearance between valve stem and valve guide - 0.030 to 0.057 mm / 0.00118 to 0.00224 in. Valve stem O.D. - 5.968 to 5.980 mm / 0.23496 to 0.23543 in. Valve guide I.D. - 6.010 to 6.025 mm / 0.23661 to 0.23720 in.

Replacing Valve Guide

Press out the used valve guide using a valve guide replacing tool. Clean a new valve guide and valve guide bore, and apply engine oil to them. Press in a new valve guide using a valve guide replacing tool. Ream precisely the I.D. of the valve guide to the specified dimension. Valve guide I.D. (Intake and exhaust) - 6.010 to 6.025 mm / 0.23661 to 0.23720 in.

Valve Seating

Coat the valve face lightly with prussian blue and put the valve on its seat to check the contact. If the valve does not seat all the way around the valve seat or the valve contact is less than 70 %, correct the valve seating as follows. If the valve contact does not comply with the reference value, replace the valve or correct the contact of valve seating.

Correcting Valve and Valve Seat

Before correcting the valve and seat, check the valve stem and the I.D. of valve guide section, and repair them if necessary. After correcting the valve seat, be sure to check the valve recessing. Correct the valve with a valve refacer. Slightly correct the seat surface with a 0.785 rad (45°) valve seat cutter. Fitting the valve, check the contact position of the valve face and seat surface with prussian blue. Grind the upper surface of the seat with a 0.262 rad (15°) valve seat cutter until the valve seat touches to the center of the valve face. Grind the seat with a 0.785 rad (45°) valve seat cutter again, and visually recheck the contact between the valve and seat. Repeat steps 3 and 4 until the correct contact is achieved. Continue lapping until the seated rate becomes more than 70 % of the total contact area.

Kubota BX2350, BX2370, BX2380 - Valve Lapping

Apply compound evenly to the valve lapping surface. Insert the valve into the valve guide. Lap the valve onto its seat with a valve flapper or screwdriver. After lapping the valve, wash the compound away and apply oil, then repeat valve lapping with oil. Apply prussian blue to the contact surface to check the seated rate. If it is less than 70 %, repeat valve lapping again.

Free Length and Tilt of Valve Spring

Measure the free length of valve spring with vernier calipers. If the measurement is less than the allowable limit, replace it. Put the valve spring on a surface plate, place a square on the side of the valve spring. Check to see if the entire side is in contact with the square. Rotate the valve spring and measure the maximum tilt. If the measurement exceeds the allowable limit, replace it. Check the entire surface of the valve spring for scratches. If there is any defect, replace it. Tilt - Allowable limit 1.2 mm / 0.047 in. Free length - 31.3 to 31.8 mm / 1.232 to 1.252 in.

Valve Spring Setting Load

Place the valve spring on a tester and compress it to the same length it is actually compressed the engine. Read the compression load on the gauge. If the measurement is less than the allowable limit, replace it.

Oil Clearance between Rocker Arm and Rocker Arm Shaft

Measure the rocker arm shaft O.D. with an outside micrometer. Measure the rocker arm I.D. with an inside micrometer, and then calculate the oil clearance. If the oil clearance exceeds the allowable limit, replace the rocker arm and measure the oil clearance again. If it still exceeds the allowable limit, replace also the rocker arm shaft. Oil clearance between rocker arm and rocker arm shaft - 0.016 to 0.045 mm / 0.00063 to 0.00177 in. Rocker arm shaft O.D. - 10.473 to 10.484 mm / 0.41232 to 0.41276 in. Rocker arm I.D. - 10.500 to 10.518 mm / 0.41339 to 0.41410 in.

Push Rod Alignment

Place the push rod on V blocks. Measure the push rod alignment. If the measurement exceeds the allowable limit, replace the push rod. Push rod alignment - Allowable limit 0.25 mm / 0.0098 in.

Oil Clearance between Tappet and Tappet Guide Bore

Measure the tappet O.D. with an outside micrometer. Measure the I.D. of the tappet guide bore with a cylinder gauge, and calculate the oil clearance. If the oil clearance exceeds the allowable limit or the tappet is damaged, replace the tappet. Oil clearance between tappet and tappet guide bore - 0.016 to 0.052 mm / 0.00063 to 0.00205 in. Tappet O.D. - 17.966 to 17.984 mm / 0.70732 to 0.70803 in. Tappet guide bore I.D. - 18.000 to 18.018 mm / 0.70866 to 0.70937 in.

Kubota BX2350, BX2370, BX2380 - Timing Gears

Timing Gear Backlash

Set a dial indicator (lever type) with its tip on the gear tooth. Move the gear to measure the backlash, holding its mating gear. If the backlash exceeds the allowable limit, check the oil clearance of the shaft and the gear. If the oil clearance is proper, replace the gear. Backlash between idle gear and crank gear - 0.043 to 0.124 mm / 0.00169 to 0.00488 in. Backlash between idle gear and cam gear - 0.047 to 0.123 mm / 0.00185 to 0.00484 in. Backlash between idle gear and injection pump gear - 0.046 to 0.124 mm / 0.00181 to 0.00488 in. Backlash between oil pump drive gear and crank gear - 0.041 to 0.123 mm / 0.00161 to 0.00484 in.

Idle Gear Side Clearance

Set a dial indicator with its tip on the idle gear. Measure the side clearance by moving the idle gear to the front and rear. If the measurement exceeds the allowable limit, replace the idle gear collar. Idle gear side clearance - 0.20 to 0.51 mm / 0.0079 to 0.0201 in.

Camshaft Side Clearance

Set a dial indicator with its tip on the camshaft. Measure the side clearance by moving the cam gear to the font and rear. If the measurement exceeds the allowable limit, replace the camshaft stopper. Camshaft side clearance - 0.15 to 0.31 mm / 0.0059 to 0.0122 in.

Camshaft Alignment

Support the camshaft with V blocks on the surface plate at both end journals. Set a dial indicator with its tip on the intermediate journal. Measure the camshaft alignment. If the measurement exceeds the allowable limit, replace the camshaft. Camshaft alignment - Allowable limit 0.01 mm / 0.0004 in.

Cam Height

Measure the height of the cam at its highest point with an outside micrometer. If the measurement is less than the allowable limit, replace the camshaft. Cam height of intake and exhaust - 26.88 mm / 1.0583 in.

Oil Clearance of Camshaft Journal

Measure the camshaft journal O.D. with an outside micrometer. Measure the cylinder block bore I.D. for camshaft with a inside micrometer, and calculate the oil clearance. If the oil clearance exceeds the allowable limit, replace the camshaft. Oil clearance of camshaft journal - 0.050 to 0.091 mm / 0.00197 to 0.00358 in. Camshaft journal O.D. - 32.934 to 32.950 mm / 1.29661 to 1.29724 in. Camshaft Bearing I.D. (Cylinder block bore I.D.) - 33.000 to 33.025 mm / 1.29921 to 1.30020 in.

Oil Clearance between Idle Gear Shaft and Idle Gear Bushing

Measure the idle gear shaft O.D. with an outside micrometer. Measure the idle gear bushing I.D. with an inside micrometer, and calculate the oil clearance. If the oil clearance exceeds the allowable limit, replace the bushing. If it still exceeds the allowable limit, replace the idle gear shaft. Oil clearance between idle gear shaft and idle gear bushing 0.020 to 0.084 mm / 0.00079 to 0.00331 in. Idle gear shaft O.D. - 19.967 to 19.980 mm / 0.78610 to 0.78661 in. Idle gear bushing I.D. - 20.000 to 20.051 mm / 0.78740 to 0.78941 in.

Replacing Idle Gear Bushing

Press out the used idle gear bushing using an idle gear bushing replacing tool. Clean a new idle gear bushing and idle gear bore, and apply engine oil to them. Press in a new brushing using an idle gear bushing replacing tool, until it is flush with the end of the idle gear.

Kubota BX2350, BX2370, BX2380 - Piston and Connecting Rod

Piston Pin Bore I.D.

Measure the piston pin bore I.D. in both the horizontal and vertical directions with a cylinder gauge. If the measurement exceeds the allowable limit, replace the piston. Piston pin bore I.D. - 20.000 to 20.013 mm / 0.78740 to 0.78791 in.

Oil Clearance between Piton Pin and Small End Bushing

Measure the piston pin O.D. where it contacts the bushing with an outside micrometer. Measure the small end bushing I.D. with an inside micrometer, and calculate the oil clearance. If the oil clearance exceeds the allowable limit, replace the bushing. If it still exceeds the allowable limit, replace the piston pin. Oil clearance between piston pin and small end bushing - 0.014 to 0.038 mm / 0.00055 to 0.00150 in. Piston pin O.D. - 20.002 to 20.011 mm / 0.78748 to 0.78783 in. Small end bushing I.D. - 20.025 to 20.040 mm / 0.78839 to 0.78897 in.

Replacing Small End Bushing

Press out the used bushing using a small end bushing replacing tool. Clean a new small end bushing and small end hole, and apply engine oil to them. Using a small end bushing replacing tool, press in a new bushing taking due care to see that the position of the connecting rod oil hole matches the bushing hole. Oil clearance between piston pin and small end bushing - 0.015 to 0.075 mm / 0.00059 to 0.00295 in. Small end bushing I.D. - 20.026 to 20.077 mm / 0.78843 to 0.79043 in.

Connecting Rod Alignment

Since the I.D. of the connecting rod small end bushing is the basis of this check, check bushing for wear beforehand. Install the piston pin into the connecting rod. Install the connecting rod on the connecting rod alignment tool. Put a gauge over the piston pin, and move it against the face plate. If the gauge does not fit squarely against the face plate, measure the space between the pin of the gauge and the face plate. If the measurement exceeds the allowable limit, replace the connecting rod. Connecting rod alignment - Allowable limit 0.05 mm / 0.0020 in.

Piston Ring Gap

Insert the piston ring into the lower part of the cylinder (the least worn out part) with a piston ring compressor and piston. Measure the ring gap with a feeler gauge. If the measurement exceeds the allowable limit, replace the piston ring. Top ring - 0.20 to 0.35 mm / 0.0079 to 0.0138 in. Second ring - 0.35 to 0.50 mm / 0.0138 to 0.0197 in. Oil ring - 0.20 to 0.35 mm / 0.0079 to 0.0138 in.

Clearance between Piston Ring and Piston Ring Groove

Clean the rings and the ring grooves, and install each ring in its groove. Measure the clearance between the ring and the groove with a feeler gauge. If the clearance exceeds the allowable limit, replace the piston ring. If the clearance still exceeds the allowable limit after replacing the ring, replace the piston. Second ring - 0.090 to 0.120 mm / 0.00354 to 0.00472 in. Oil ring - 0.04 to 0.08 mm / 0.0016 to 0.0031 in.

Kubota BX2350, BX2370, BX2380 - Crankshaft

Crankshaft Side Clearance

Set a dial indicator with its tip on the end of the crankshaft. Measure the side clearance by moving the crankshaft to the front and rear. If the measurement exceeds the allowable limit, replace the thrust bearings. If the same size bearing is useless because of the crankshaft journal wear, replace it with an oversize one. Crankshaft side clearance - 0.15 to 0.31 mm / 0.0059 to 0.0122 in.

Crankshaft Alignment

Support the crankshaft with V blocks on the surface plate at both end journals. Set a dial indicator with its tip on the intermediate journal. Measure the crankshaft alignment. If the measurement exceeds the allowable limit, replace the crankshaft. Crankshaft alignment - Allowable limit 0.02 mm / 0.0008 in.

Oil Clearance between Crankpin and Crankpin Bearing

Clean the crankpin and crankpin bearing. Put a strip of plastigage on the center of the crankpin. Install the connecting rod cap and tighten the connecting rod screws to the specified torque, and remove the cap again. Measure the amount of the flattening with the scale, and get the oil clearance. If the oil clearance exceeds the allowable limit, replace the crankpin bearing. If the same size bearing is useless because of the crankpin wear, replace it with an undersize one referring to the table and figure. Be sure not to move the crankshaft while the connecting rod screws are tightened. Oil clearance between crankpin and crankpin bearing - 0.020 to 0.051mm / 0.00079 to 0.00201 in. Crankpin O.D. - 33.959 to 33.975 mm / 1.33697 to 1.33760 in. Crankpin bearing I.D. - 33.995 to 34.010 mm / 1.33839 to 1.33898 in.

Oil Clearance between Crankshaft Journal and Crankshaft Bearing 1

Measure the O.D. of the crankshaft front journal with an outside micrometer. Measure the I.D. of the crankshaft bearing 1 with an inside micrometer, and calculate the oil clearance. If the oil clearance exceeds the allowable limit, replace the crankshaft bearing 1. Oil Clearance between crankshaft journal and crankshaft bearing 1 - 0.034 to 0.106 mm / 0.00134 to 0.00417 in.

Oil Clearance between Crankshaft Journal and Crankshaft Bearing 2 and Crankshaft Bearing 3

Put a strip of plastigage on the center of the journal. Install the bearing case and tighten the bearing case screws 1 to the specified torque, and remove the bearing case again. Measure the amount of the flattening with the scale, and get the oil clearance. If the oil clearance exceeds the allowable limit, replace the crankshaft bearing 2 (crankshaft bearing 3). Oil clearance between crankshaft journal and crankshaft bearing 2 (crankshaft bearing 3) - 0.028 to 0.059 mm / 0.00110 to 0.00232 in. Crankshaft journal O.D. (Flywheel side) - 43.934 to 43.950 mm / 1.72968 to 1.73031 in. Crankshaft bearing 2 I.D. - 43.978 to 43.993 mm / 1.73142 to 1.73201 in.