Specifications, Service and Repair of Farm and Lawn Tractors

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Kubota B5200, B7100, B7100HST - Engine Service

Kubota B5200, B7100, B7100HST - Fuel System

Replacing Filter Element

B5200, B7100, B7100HST tractors are equipped with a Kubota D750 3 Cylinder Diesel Engine. Before replacing the filter element, shut-off the fuel supply to the filter by turning the fuel cock lever straight up and do the following: Loosen retaining ring from filter housing. Remove filter cup and О-ring from filter housing. Remove filter element and О-ring and then install a new element in its place. Thoroughly clean filter cup. Be sure that O-ring seal is in good condition and install on filter cup. Install filter cup, being careful not to overtighten retaining ring. Turn on fuel supply. Open vent plug on filter. Tighten plug when fuel flows free of bubbles.

Checking Nozzle Opening Pressure

Move the tester handle up and down to prime fuel. Measure the pressure of fuel gushing out from the nozzle tip. If the measurement is not within the reference value, adjust with the adjustment washer inside the nozzle holder. An increase of every 0.1 mm (0,004 in.) of washer thickness causes an approximate 980 kPa (10 kgf/cm2, 142 psi) increase in fuel injection pressure.

Checking Injection Timing

Check fuel injection timing of the cylinder approaching the expansion stroke by manually turning the engine flywheel. Check if fuel is injected at the moment the mark on the flywheel. If fuel injection timing is improper, adjust with shims to change the position of the injection pump. If injection is too late take off shim. Each shim will cause proceeding of 0.026 rad. (1.5°). Shim thickness: 0.12 to 0.18 mm (0.0047 to 0.0071 in.). Reference value - Before TDC (Top Dead Center) 0.401 to 0.436 rad. (23° to 25°) (at the beginning of static injection).

Checking Fuel Pipe

If the damp is loose, apply oil to the threads and securely retighten it. The fuel pipe is made of rubber and ages regardless of the period of service. Change the fuel pipe together with the clamp every two years. However, if the fuel pipe and damp are found to be damaged or deteriorate earlier than two years, then change or remedy. After the fuel pipe and the clamp have been changed, bleed the fuel system. When bleeding fuel system - Fid the fuel tank with fuel, and open the fuel cock. Loosen the air vent plug of the fuel filter a few turns. Screw back the plug when bubbles do not come up any more. Open the air vent cock on top of the fuel injection pump. Retighten the plug when bubbles do not come up any more.

Fuel Filter Cleaning

Water and grit present in the fuel will be extracted by the fuel filter. When the filter is blocked/full, turn off the fuel tap, remove and clean the filter. Air must always be removed when refitting the filter as follows: Turn the fuel filter to the ON position. Open the taps as follows - At the top of the injection pump. At the top of the fitter. Half fill the tank. Turn the filter tap off. Fill the tank up to the top. Run the engine for one minute then stop it. Turn off the pump tap. Only open the pump tap and filter tap when draining.

Cleaning Air Cleaner



The air cleaner uses a dry element. Never apply oil to it. Remove and clean out the dust cup before it becomes balf full with dust. When the air filter element is dusty, clean it. Change the element once a year or every 6th cleaning. Install the air cleaner dust cup with "TOP” indicated on the rear of the cup in the upside. If the dust cup is mounted incorrectly, dust or dirt does not collect in the cup, and direct attachment of the dust to the element will cause its life time to shorten to a great extent.

Cleaning Air Filter Element

When dry dust adheres. Use dean dry compressed air on the inside of the element. Air pressure at the nozzle must not exceed 690 kPa (7kgf/cm2, 100psi). Maintain reasonable distance between the nozzle and the filter.

Cleaning Fuel Filter

Close the fuel filter cock. Unscrew the screw ring and remove the cup, and rinse the inside with kerosene.

Checking 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. If the spraying condition is defective, replace the nozzle piece. Pressure variation with 0.1 mm (0.0039 in.) difference of adjusting washer thickness. Approx. 981 kPa (10 kgf/cm2, 142 psi).

Removing Pumps

Detach the fuel pump. Detach the hydraulic pump. Do not hit the cap of idling limit apparatus. Remove the injection pump cover. Remove one end of the governor spring from the fork lever and leave it there. Remove the nuts and bolts holding the injection pump. Detach the injection pump. To prevent the pump rack from being caught, detach the pump along the removal groove. Count the number of the fuel injection timing adjusting shims.

Kubota B5200, B7100, B7100HST - Engine Oil and Oil Filter

Checking Kubota D750 Engine Oil Level

Level the engine. To check the oil level, draw out the dipstick, wipe it clean, reinsert it, and draw it out again. Check to see that the oil level lies between the two notches. If the level is too low, add new oil to the specified level. When checking the oil level, make sure the tractor is on a flat surface. It is impossible to check accurately if the tractor is not level. Check the oil level before starting or more than 3 minutes after the engine has stopped. At other times, the check will not be accurate as oil stagnates in certain engine parts. When using an oil of different maker or viscosity from the previous one, drain old oil. Never mix two different types of oil.

Changing Engine Oil

After warming up, stop the engine. To change the used oil, remove the drain plug at the bottom of the engine and drain off the oil completely. Reinstall the drain plug. Fill the new oil up to the upper notch on the dipstick. Change the type of engine oil according to the ambient temperature. Above 25C - SAE 30 or 10W-30, 0C to 25C - SAE 20 or 10W-30, Below 0C - SAE 10 W or 10W-30.

Changing Kubota D750 Engine Oil Filter Cartridge

Remove the oil filter cartridge with a filter wrench. Apply engine oil to the rubber gasket on the new cartridge. Screw the new cartridge in by hand. Over-tightening may cause deformation of rubber gasket. After cartridge has been replaced, engine oil normally decreases a little. Check the oil level and add new oil to the specified level.

Removing Gear Case, Camshaft, and Oil Pump

Remove the four bolts holding the speed control plate. Lift the plate to detach. Remove the start spring near the gear case with a pair of cutting pliers. Remove tie fan drive pulley with a puller. Remove the gear case. Make sure there are three O-rings inside the gear case. Remove the idler gear. Remove the camshaft stopper. Remove the camshaft by drawing out the cam gear. Remove the fuel camshaft stopper. Remove the fork lever holder and fork lever assembly. Draw out the fuel camshaft and the injection pump gear. Set a gear puller on the oil pump drive gear. Draw out the gear. Remove the oil pump. Remove the crank gear with a gear puller.

Kubota B5200, B7100, B7100HST - Cooling System

Radiator Cap Air Leakage

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

Thermostat

Remove the thermostat cover. Remove the thermostat. Apply a liquid gasket only at the thermostat cover side of the gasket.

Kubota D750 Water Pump



Remove the fan and fan pulley. Remove the water pump from gear case cover. Remove the water pump flange. Press out the water pump shaft with the impeller on it. Remove the impeller from the water pump shaft. Remove the mechanical seal. Replace the mechanical seal with new one.

Checking and Replenish Cooling Water

Remove the radiator cap and check to see that the cooling water level is just bellow the port. If low, add clean water and antifreeze. Be sure to close the radiator cap securely. If the cap is loose or improperly closed, water may leak out and the engine could overheat. Do not use an antifreeze and scale inhibitor at the same time.

Checking Fan Belt Tension and Checking Fan Belt Damage

Check the fan belt for damage. Check if the fan belt is worn and sunk in the pulley groove. Replace the fan belt if the belt is damaged or nearly worn out and deeply sunk in the pulley groove. Press the Ian belt between fan pulley and pulley with your finger at force of 98N (10 kgf, 22 Ibs). Check if the fan belt deflection is 7 to 9 mm (0.28 to 0.35 in.). If the deflection is not within the factory specifications, adjust with the tension pulley adjusting bolts.

Kubota B5200, B7100, B7100HST - Cylinder Block and Cylinder Head

Cylinder Block

Dry-type cylinder liners are pressure-fitted into the cylinders to reduce distortion and uneven wear and provide less operating noise and lower oil consumption. To minimize noise, each cylinder has its own crank chamber. The tunnel-type cylinder block is also more durable.

Cylinder Head

Inlet and exhaust ports are of cross-flow type to prevent air expansion due to exhaust heat. The spherical combustion chambers provide a vortex flow of air which enters the combustion chamber to improve combustion and reduce fuel consumption. The sheathed type glow plug heats quickly and assures good starting.

Kubota D750 Cylinder Head Disassembly

Remove the head cover nuts. Remove the head cover. Loosen the tension pulley shaft set nut. Loosen the tension bolt for the tension pulley and remove the V-belt. Loosen the screws on the pipe clamp. Detach the injection pipes in the order of 1, 2 and 3. Remove the clips holding the fuel overflow pipes, and detach the pipes. Detach the nozzle holders using a 27mm (1.063 in.) nozzle holder socket wrench. Remove the set nuts for the rocker arm brackets, and detach the rocker arm assembly. Remove the six push rods. Remove the twelve cylinder head bolts and two nuts. Remove the cylinder head. Detach the cylinder head gasket, being careful not to scratch it. Remove the О-ring from the periphery of the oil pipe pin on the crankcase. Remove the six tappets from the crankcase.

Checking Compression

Warm up the engine. Detach the air cleaner and the nozzle holders of all cylinders. Attach compression tester to the cylinder to be measured. Run the engine with the starter at engine speed 200 to 250 rpm and read the constant maximum on the tester. Repeat the test at least twice. (Run the engine for 5 to 10 seconds for each test.). Reference value: 2.7 to 3.1 MPa (28 to 32 kgf/cm2, 398 to 454 psi). Allowable limit: 2.4 Mpa (24 kgf/cm2,341 psi). When the reading is below the allowable limit, pour a small amount of oil through the nozzle holder hole, and test again. If the pressure recovers to the standard level after a while, the possible cause of the in-adequate pressure is wearing or adhesion of piston rings. Check related points. If the pressure does not recover, it may be because of cylinder head or valve problems. Check related points. If there is a difference in compression of more than 10 percent (%) among the cylinders, trace the cause of pressure variation and take corrective measures.

Checking Distortion of Cylinder Head Surface

Clean the surface of the cylinder head. Place a straight edge on the four sides and diagonal lines of the cylinder head to check surface straightness. Insert a feeler gauge between the straight edge and the cylinder head surface. The maximum thickness that can be inserted is the amount of distortion. Allowable limit: 0.05 mm (0.002 in.) per 100 mm (4 in.). Do not place a straight edge on the combustion chamber. If the measurement exceeds the allowable limit, correct with a surface grinder.

Kubota B5200, B7100, B7100HST - Checking Valves

Inlet and Exhaust Valves

The inlet and exhaust valves and their guides are different from each other. Other parts, such as valve springs, valve spring retainers, valve spring collets, valve stem seals, and valve caps are the same for both the inlet and exhaust valves. All contact or sliding parts are quenched and tempered to resist wear.

Checking Valve Recess

Clean the face of the valve. Measure the recess with a depth gauge. If a valve seat is reground many times, it will recede too far and the valve spring will stretch and lose its tension. When the valve recess becomes more than the reference value, place a washer of appropriate thickness under the spring. Reference value: 0.9 to 1.1 mm (0.035 to 0.043 in.). Allowable limit: 1,3mm (0.051 in.).

Checking Stem Guide Clearance

Remove carbon from the valve guide. After making sure that the valve stem is straight, insert the valve into the valve guide. Measure the stem guide clearance with a dial gauge. If the measurement exceeds the allowable limit, replace the stem guide and the valve. Reference value: 0.035 to 0.065 mm (0.0014 to 0.0026 in.). Allowable limit: 0.1 mm (0.004 in.). When replacing valve guides, make sure that they are installed on the proper sides.

Checking Valve Spring Inclination

Put the spring on a surface plate, place a square on the side of the spring, and check to see if the entire side is in contact with the square. Rotate the spring and measure the maximum. The flat surface at the end of the spring coil must be at least 2/3 more than the full circumference. Check the entire surface of the spring for scratches. If the measurement exceeds the allowable limit, replace the valve spring. Allowable limit: 1.3 mm (0.051 in.).

Kubota B5200, B7100, B7100HST - Pistons, Piston Rings and Crankshaft

Piston

Piston circumference has a special elliptic shape in consideration of expansion due to explosion heat. Furthermore, a rib is provided between the piston head and the piston boss to reduce distortion and to help heat radiation. Three piston rings are used: two compression rings, and an oil ring. All have different shapes. Be careful when assembling.

Crankshaft



The crankshaft is driven by the pistons and connecting rods, and translates its reciprocating movement into a circular movement. It also drives the oil pump, camshaft, and fuel camshaft. Crankshaft journals are supported by main bearings. Six counterweights are integrated into one unit to minimize bearing wear and lubricating oil temperature rise. Crankshaft journals and the oil seal's sliding sections are quenched and tempered to improve wear resistance.

Kubota D750 - Removing Piston and Crankshaft

Remove the eighteen oil pan mounting bolts, and detach the oil pan. Detach the oil filter, being careful of the O-ring. Remove the connecting rod bolts and large end metal, turn the crankshaft by 180°, 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 handle of a hammer. After drawing the piston out, attach a tag to each piston indicating its number. Remove the piston rings. Set Flywheel Puller, and remove the flywheel. Remove the bearing case cover mounting bolts. Screw the two removed bolts into the right and left holes of the bearing case cover, to pull off the cover by lifting it up. Detach the bearing case bolts 2 under the crankcase. Draw out the crankshaft from the back of the crankcase by lightly tapping it with a copper hammer. Detach the main bearing cases, being careful with the side and crankshaft metals. Grind the cylinder head mounting surface with an oil stone. Set the dry liner centering base and adaptor on the frame head. Set the dry liner centering base. Set the bearing cradle on the liner centering base with the bearing on top. Insert the pulling-out adaptor coupling, and fix the center bolt. Contact the pulling-out adaptor with the bottom of the liner from the bottom of the crankcase. Pull out the liner by turning the nut with a ratchet handle.

Checking Top Clearance

Remove the nozzle holder. Lower the piston in the cylinder to be measured. Insert a high-quality fuse from the nozzle holder hole. Be careful not to let the fuse touch the valve surface. Rotate the engine by hand. Take the fuse out carefully. Measure the place where the fuse was crushed with a set of vernier calipers. If the measurement is not within the reference value, adjust by inserting a shim between the cylinder head and the gasket. Reference value 0.6 to 0.8 mm (0.0237 to 0.031 5 in.).

Kubota B5200, B7100, B7100HST - Camshaft and Rocker Arm

Camshaft and Fuel Camshaft

The camshaft is made of special cast iron and the journal and cam sections are chilled to resist wear. The journal section is force-lubricated. The fuel camshaft controls the reciprocating movement of the injection pump and is equipped with a ball to control the governor. The shaft end drives the hydraulic pump for implement lifting. Fuel camshaft is made of carbon steel and journal and cam sections are quenched and tempered to provide greater wear resistance.

Rocker Arm Assembly

The rocker arm assembly includes the rocker arms, rocker arm brackets and rocker arm shaft, and converts the reciprocating movement of the camshaft and push rods to an open/close movement of the inlet and exhaust valves. Valve control timing must be adjusted with the screws on the rocker arms. Lubrication oil is pressurized through the bracket to the rocker arm shaft, which serves as a fulcrum so that the rocker arm bearings and the entire system are lubricated sufficiently.

Checking Oil Clearance between Rocker Arm Shaft and Bushing

Measure the inside diameter of the rocker arm bushings. Measure the outside diameter of the rocker arm shaft and then calculate the clearance. If the measurement exceeds the allowable limit, replace the bushing. Rocker arm shaft O.D: 10.973 to 10.984 mm (0.4320 to 0.4324 in.). Rocker Arm bushing I.D: 10.997 to 11.038 mm (0.4330 to 0.4346 in.). Reference value: 0.013 to 0.065 mm (0.0005 to 0.0026 in.). Allowable limit: 0.12 mm (0.0047 in.).

Checking Cam Heights of Intake and Exhaust

Place the camshaft on V-blocks. Attach a dial gauge to the journal. While slowly rotating the camshaft, read the dial gauge. The camshaft flexure is a half of the reading. If the measurement exceeds the allowable limit, replace the camshaft. Allowable limit: 0.08 mm (0.0031 in.).

Checking Wear of Fuel Camshaft Cams

Place the fuel camshaft on V-blocks. Measure the cam height with a micrometer. If the measurement exceeds the allowable limit, replace the camshaft. Reference value: 30,93 to 31.07 mm (1.2177 to 1.2233 in.). Allowable limit: 30.87 mm (1.2154 in.).

Checking Clearance between Idle Gear Shaft and Idle Gear Bushings

Measure the idle gear shaft O.D. with an outside micrometer. Measure the idle gear bushings I.D. with an inside micrometer, and calculate the clearance. If the clearance exceeds the allowable limit, replace the bushing. Reference value: 0.016 to 0.045 mm (0.0007 to 0.0017 in.). Allowable limit: 0.1 mm (0.0039 in.).

Checking Backlash of Idler Gear

Install a lever-type indicator between the gear teeth. Read the indicator while manually moving the gear. If the measurement exceeds the allowable limit, replace the gear. Reference value: 0.04 to 0.12 mm (0.002 to 0.005 in.). Allowable limit: 0.2 mm (0.008 in.).

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