________________________________________________________________________________

Kubota D902 Engine body - Adjusting and servicing

Kubota D902 - Cylinder head

Checking 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. Cylinder head surface flatness: Allowable limit - 0.05 mm / 0.002 in.

Checking 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 red 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

Checking compression pressure

Check the compression pressure with the specified valve clearance. Always use a fully charged battery for performing this test. Variances in cylinder compression values should be under 10%. Operate the engine until it is warmed up. Stop D902 Engine. Remove the air cleaner, the muffler and all glow plugs (or nozzles). Set a compression tester with the adapter to the glow plug hole (or nozzle hole). Nozzle hole: Adapter H (07909-31231). Glow plug hole: Adapter L (07909-31301). Disconnect the connector of engine stop solenoid and keep the engine stop position (non-injection). Then, operate the engine with the starter and measure the compression pressure. Repeat steps 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. Compression pressure: Factory specification - 3.53 to 4.02 MPa / 512 to 583 psi. Allowable limit - 2.55 MPa / 370 psi. 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.

Checking cylinder wear

Measure the I.D. of the cylinder at the six positions with a cylinder gauge to find the maximum and minimum I.D.'s. Get the difference (maximum wear) between the maximum and the minimum I.D.'s. If the wear exceeds the allowable limit, bore and hone to the oversize dimension. Cylinder liner I.D - 72.000 to 72.019 mm / 2.8347 to 2.8353 in. Visually check the cylinder wall for scratches. If deep scratches are found, the cylinder should be bored.

Kubota D902 - Valves

Checking valve clearance

Valve clearance must be checked and adjusted when engine is cold. The sequence of cylinder numbers is given as No. 1, No. 2 and No. 3 starting from the gear case side. After adjusting the valve clearance, secure the adjusting screw with the lock nut. Remove the cylinder head cover and the glow plugs. Align the 1TC mark at 1TC and timing line 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 with 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. Then turn the flywheel 6.28 rad (360°), and align the 1TC mark at 1TC and timing line 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 with using a feeler gauge. If the clearance is not within the factory specifications, adjust with the adjusting screw.

Checking top clearance

Remove the cylinder head. With the piston at T.D.C., use grease to affix three or four plastigauges of a diameter 1.5 mm (0.059 in.) x 5.0 to 7.0 mm (0.20 to 0.27 in.) long to the crown of the piston; keep the gauges away from the intake valve and combustion chamber fittings. Take the piston to an intermediate position, install the cylinder head and tighten the head bolts to the specified torque. Cylinder head screw - 38 to 42 Nm / 28 to 31 lbf-ft. Turn the crankshaft so the piston goes through T.D.C. Remove the cylinder head and compare the width of the crushed plastigauges with the scale. If they are out of specification, check the oil clearance of the crank pin, journals and piston pins. Top clearance (Kubota D902 engine for BX2370, BX2380, BX2230, BX2350, BX2360, BX23, BX23S, BX24, BX25, BX25D tractors) - 0.55 to 0.70 mm / 0.022 to 0.027 in.

Checking 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. Valve recessing: Factory specification - 0.10 (protrusion) to 0.10 (recessing) mm / 0.0039 (protrusion) to 0.0039 (recessing) in. Allowable limit 0.30 (recessing) mm / 0.012 (recessing) in. If it still exceeds the allowable limit after replacing the valve, replace the cylinder head.

Checking clearance between valve stem and valve guide

Remove carbon from the valve guide section. Measure the valve stem O.D. with an outside micrometer. Valve stem O.D - 5.968 to 5.980 mm / 0.2350 to 0.2354 in. Measure the valve guide I.D. with a small hole gauge, and calculate the clearance. Valve guide I.D - 6.010 to 6.025 mm / 0.2367 to 0.2372 in. 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 (Kubota D902 engine for BX2370, BX2380, BX2230, BX2350, BX2360, BX23, BX23S, BX24, BX25, BX25D tractors): Factory specification - 0.030 to 0.057 mm / 0.0012 to 0.0022 in. Allowable limit 0.10 mm / 0.0039 in. Replacing valve guide - 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 / 0.2367 to 0.2372 in.

Checking 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. Valve seat width - 2.12 mm / 0.835 in. Correcting valve seat - Slightly correct the seat surface with a 1.0 rad (60 deg) (intake valve) or 0.79 rad (45 deg) (exhaust valve) valve seat cutter. Valve seat angle - 0.79 rad / 45 deg. Resurface the seat surface with a 0.52 rad (30 deg) valve seat cutter to intake valve seat and with a 0.26 rad (15 deg) valve seat cutter to exhaust valve seat so that the width is close to specified valve seat width (2.12 mm, 0.0835 in.). After resurfacing the seat, inspect for even valve seating, apply a thin film of compound between the valve face and valve seat, and fit them with valve lapping tool. Check the valve seating with prussian blue. The valve seating surface should show good contact all the way around.

Lapping valve

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. Checking valve spring setting load - Place the valve spring on a tester and compress it to the same length it is actually compressed in the engine. Read the compression load on the gauge. If the measurement is less than the allowable limit, replace it. Setting load / Setting length: Factory specification - 65 N / 27.0 mm (15 lbf / 1.06 in.). Allowable limit - 55 N / 27.0 mm (12 lbf / 1.06 in.).

Kubota D902 - Rocker arm and rod

Checking oil clearance between rocker arm and rocker arm shaft - Measure the rocker arm shaft O.D. with an outside micrometer. Rocker arm shaft O.D - 10.473 to 10.484 mm / 0.41233 to 0.41275 in. Measure the rocker arm I.D. with an inside micrometer, and then calculate the oil clearance. Rocker arm I.D - 10.500 to 10.518 mm / 0.41339 to 0.41409 in. 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 (Kubota D902 engine for BX2370, BX2380, BX2230, BX2350, BX2360, BX23, BX23S, BX24, BX25, BX25D tractors) - 0.016 to 0.045 mm / 0.00063 to 0.0017 in. Checking 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.

Kubota D902 - Gear and camshaft

Checking 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 shafts and the gear. Backlash between idle gear and crank gear - 0.0430 to 0.124 mm / 0.00170 to 0.00488 in. Backlash between idle gear and cam gear - 0.0470 to 0.123 mm / 0.00185 to 0.00484 in. Backlash between idle gear and injection pump gear - 0.0460 to 0.124 mm / 0.00182 to 0.00488 in. Backlash between oil pump drive gear and crank gear - 0.0410 to 0.123 mm / 0.00162 to 0.00484 in. If the oil clearance is proper, replace the gear.

Checking idle gear 1 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 1 side clearance 0.20 to 0.51 mm / 0.0079 to 0.020 in.

Checking camshaft side clearance

Set a dial indicator with its tip on the camshaft. Measure the side clearance by moving the cam gear to the front to rear. If the measurement exceeds the allowable limit, replace the camshaft stopper. Camshaft side clearance (Kubota D902 engine for BX2370, BX2380, BX2230, BX2350, BX2360, BX23, BX23S, BX24, BX25, BX25D tractors) - 0.15 to 0.31 mm / 0.0059 to 0.012 in.

Checking 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. Checking oil clearance of camshaft journal - Measure the camshaft journal O.D. with an outside micrometer. Camshaft journal O.D - 32.934 to 32.950 mm / 1.2967 to 1.2972 in. Measure the cylinder block bore I.D. for camshaft with a cylinder gauge, and calculate the oil clearance. Camshaft bearing I.D. (Cylinder block bore I.D.) - 33.000 to 33.025 mm / 1.2993 to 1.3001 in. If the oil clearance exceeds the allowable limit, replace the camshaft. Oil clearance of camshaft journal - 0.050 to 0.091 mm / 0.0020 to 0.0035 in.