ThisWorkshop Manual has been prepared to provide servicing personnel with information on the mechanism, service and maintenance of KUBOTA Diesel Engines 70 mm STROKE SERIES. It is divided into two parts, "Mechanism" and "Disassembling and Servicing".


DIMENSIONS  see manual

Information on construction and functions are included for each engine section. This part should be understood before proceeding with trouble- shooting, disassembling and servicing.

Disassembling and Servicing
Under the heading "General" come general precautions, troubleshooting,
lists of servicing specifications and periodic inspection items. For each engine section, there are If Checking and Adjustment", If Disassembllng and Assembling", and "Servicing" which cover procedures, precautions, factory specification and allowable limits.

All information, illustrations and specifications contained in this manual are based on the latest production information available at the time of publication. The right is reserved to make changes in all information at any time without notice.
Due t o covering many models of this manual, illustration or picture being used have not been specified as one model.
Apr. '88



The 70 mm STROKE SERIES ENGINE are vertical, water-cooled, 4-cycle diesel engines.
They are incorporated KUBOTA's foremost technologies. With KUBOTA's spherical combustion chamber, well-known Bosch K type injection pump and the well-balanced designs, they give greater power, low fuel consumption, little vibration and quiet operation.


The engine has a high durability tunnel-type cylinder in which the crank bearing component is a constructed body. Furthermore, dry-type cylinder liners, being pressure-fitted into cylinders, allow effective cooling, less distortion, and greater wear- resistance. The noise level is reduced to a
minimum because each cylinder has its own chamber.

The cross-flow type intakelexhaust ports in this engine have their openings at both sides of the cylinder head. Because overlaps o f intake/exhaust ports are smaller than in ports of other types which have openings on one side, the suction air can be protected from being heated and expanded by heatedexhaustair. Thecool,highdensitysuctionair has high volume efficiency and raises the power of the engine. Furthermore, distortion of the cylinder head by heated exhaust gas is reduced because intake ports are arranged alternately. The combustion chamber is of KUBOTA's exclusive spherical combustion chamber type. Suction air is whirled t o be mixed effectively with fuel, prompting combustion and reducing fuel consumption.

In the combustion chamber are installed throttle type injection nozzle and rapid heating sheathed type glow plug. This glow plug assures easier than ever engine starts even at-15C(5F).

(1) CombustionChamber
(2) Intake Port
(3) Exhaust Port
(4) Nozzle Assembly
(5) Glow Plug
(6) Cylinder Head

The crankshaft with the connecting rod converts the reciprocating motion of the piston into the rotating motion.
The crankshaft i s made of tough special alloy steel, and the journals, pins and oil seal sliding portions are induction hardened t o 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 crank pin portion, and lubricate it.

The piston has a slightly oval shape when cold (in consideration of thermal expansion) and a flat head.
Three rings are installed in grooves in the piston.
Thetopring(1) isakeystonetype,whichcanstand against heavy loads, and the barrel face on the ring fits well t o the cylinder wall.
The second ring (2) is an undercut type, which effectively prevents the oil from being carried up.
The oil ring (3) has chamfered contact faces and an expander ring, which increase the pressure of the oil ring against the cylinder wall.
Several grooves are cut on,the topland to help heat dissipate and t o prevent scuffing.

( I ) Top Ring
(2) Second Ring
(3) Oil Ring

Connecting rod (2) is used to connect the piston with the crankshaft. The big end of the connecting rod has a crank pin bearing (3) (split type) and the small end has a small end bushing (1) (solid type).

(1) Small End Bushing
(2) ConnectingRod
(3) Crank pin Bearing
(4) ConnectingRod Cap

The camshaft (3) is made of special cast iron and the journal and cam sections are chilled to resist wear. The journal sections are force-lubricated.

The fuel camshaft (8) controls th e reciprocating movement of the injection pump, and is equipped with a ball to control the governor. The fuel camshaft is made of carbon steel and the cam sections are quenched and tempered to provide greater wear resistance.
(1). Cam Gear
(2) Camshaft Stopper
(3) Camshaft
(4) Injection Pump Gear
(5) Governor Sleeve
(6) Fuel Camshaft Stopper
(7) Ball Bearing
(8) Fuel  Camshaft
(9) Steel Ball

The flywheel stores the rotating force in the combustion stroke as inertial energy, reduces crankshaft rotating speed fluctuation and maintains th e smooth rotating conditions.
The flywheel periphery is inscribed with t h e marks showing fuel injection timing angle lines and top dead center mark TC.
The flywheel has gear teeth around its outer rim, which mesh with the drive pinion of the starter.
(1) Crankshaft
(2) Flywheel
(3) FlywheelScrew

The rocker arm assembly includes the rocker arms (l), rocker arm brackets (4) and rocker arm shaft (5) and converts the reciprocating movement of the push rods to an openklose 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 bearing and the entire system are lubricated sufficiently.
(1) Rocker Arm
(2) LockNut
(3) Adjusting Screw
(4) RockerArm Bracket
(5) RockerArmShaft



[A] Oil Pump
[B] Piston
[C] Rocker Arm and Rocker Arm Shaft
ID] Oil Strainer
fEJ Camshaft
[F] Oil Filter Cartridge and Reiief Valve

This engine lubricating consists of oil strainer, oil pump, relief valve, oil filter cartridge and oil switch. The oil pump sucks lubricating oil from the oil pan through the oil strainer and the oil flows down to the filter cartridge, where it is further filtered. Then the oil is forced to crankshaft, connecting rods, idl  gear, camshaft and rocker arm shaft to lubricate each part. Some  of the oil, splashed by the crankshaft or leaking and dropping from gaps above,  lubricates the following: pistons, cylinders, small ends of connecting rods, tappets, pushrods, inlet and exhaust valves and timing gears.

Engine Oil Flow

(1) Oil Pan  (2) Oil Strainer  (3) Oil Pump  (4) Relief Valve (5) Oil Filter Cartridge  6) Idle Gear
(7) Main Oil Gallery (8)Main Bearings  (9) Big End (10) Timing Gear
(11) Splash (12) Bore  (13) Small Ends (14)Pistons
(15) Fuel Camshaft (16)Tappets
(17) Camshaft Bearings  (18)Camshaft  (19)Drains
(20) RockerArm (21) Oil Switch
(22) Rocker Arm Shaft

The oil pump in this engine is a trochoid pump.
Inside the pump body, the 4 lobe inner rotor (3) is eccentrically engaged with the 5 lobe outer rotor (4). The inner rotor is driven by the crankshaft via gears, which in turn rotates 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 as shown in the figure.
At position (A), there is little space between lobes in the inlet port. As the rotor rotates towards position (B), the space between the lobes becomes larger, creating a negative pressure which sucks in oil.
Outside the inlet port, as shown in position (C), the space between the lobes becomes gradually smaller, and oil pressure increases. At position (D), oil is discharged from the outlet port.

(1) Inlet
(2) Outlet
(3) Inner Rotor
(4) OuterRotor

Impurities in engine oil can cause to wear and seize components as well as impairing the physical and chemical properties of the oil itself. Impurities contained in force-fed engine oil are absorbed on the filter paper for removal as they pass through the filter element (2)-
When the filter element is clogged and the oil pressure in inlet line builds up by 98 kPa (1.0 kgfkmz, 14 psi) more than the outlet line, the bypass valve (1) opens and the oil flows from inlet to outlet bypassing the filter element.

The relief valve  (part of [at base] the oil filter cartrage base)  prevents damage to 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 (3) is pushed back by the pressure oil and the oil escapes.
(1) O-ring
(2) Valve Seat
(3) SteelBall
(4) Spring
(5) Relief Valve Body

The oi1,pressure switch is mounted on the cylinder- block, to warn the operator that the lubricating oil pressure is poor.
If the oil pressure falls below 49kPa (0.5 kgf/cm*,7 psi), the oil warning lamp will light up, warning the operator. In this case, stop the engine immediately andcheckthecauseof pressuredrop.
[A] A t Proper Oil Pressure  light out
[B] A t Oil Pressuresof 49 kPa (0.5 kgf/cm*, 7 psi) or Less   light on

(1) Terminal
(2) Insulator
(3) Spring
(4) Diaphragm
(5) Contact Rivet
(6) Contact
(7) Oil Switch Body



(1) Radiator
(2) Suction Fan
3) Thermostat
(4) Water Pump
(5) Cylinder Head
(6) Cylinder Block

The cooling system consists of a radiator (1) (not included in the basic engine), centrifugal water pump (4), suction fan (2) and thermostat( 3).
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 drives out the hot water.
Then the cooling is repeated. A thermostat is provided in the system  to further control temperature of water, . When the thermostat  is closed (cold) , the water circulates through a bypass between thermostat and water pump, when it  opens, the water moves directly to the radiator . The opening temperature of thermostat is approx. 82C (180F).

The water pump is driven by the crankshaft via a V-belt. Water cooled in the radiator is sucked into the water pump from its lower portion and is sent from the center of the water pump impeller (4) radially outward into the water jacket in the crankcase.
(1) BearingUnit
(2) Water Pump Body
(3) Mechanical Seal
(4) Water Pump impeller