Kubota Z851

Kubota Z851The Kubota Z851 is a 867 cc (52.9 cu·in) natural aspirated two-cylinders four-stroke liquid-cooled internal combustion vertical diesel engine, manufactured by Kubota Corporation for general-purpose applications.

The cylinder bore and piston stroke are 76.0 mm (2.99 in) and 82.0 mm (3.23 in), respectively.

This engine produced 18.2 PS (13.4 kW; 18.0 HP) at 3,000 rpm of horsepower.

The Kubota Z851 features:

  • Fuel injection pump
  • Centrifugal ball mechanical governor
  • Forced lubrication by pump
  • Liquid cooling system
  • Electric starter
  • Charging alternator

General information

Engine Specifications
Engine modelZ851
Engine type4-stroke, vertical, two-cylinders
Displacement867 cm3, (52.9 cu·in)
Max. horsepower18.2 PS (13.4 kW; 18.0 HP) at 3,000 rpm
Max. torque
Cooling systemLiquid-cooled
Lubricating systemForced lubrication by pump
Combustion chamber
Fuel systemFuel injection pump
Injection typeIndirect injection
Fuel usedDiesel fuel No.2-D
Starting systemElectric starter
GovernorCentrifugal ball mechanical governor
PTO shaft rotationCounterclockwise (from PTO shaft side)
Dimensions (L x W X H)
Dry weight

Cylinder Block and Head

Cylinder block
Compression ratio:
Cylinder bore:82.0 mm (3.23 in)
Piston stroke:82.0 mm (3.23 in)
Cylinder internal diameter (standard):82.000-82.022 mm (3.2283-3.2292 in)
Piston skirt diameter (standard):
Number of piston rings (compression / oil):2/1
Piston pin diameter:23.002-23.011 mm (0.9056-0.9059 in)
Side clearance (Second):0.090-0.120 mm (0.0040-0.0050 in)
Side clearance (Oil):0.020-0.050 mm (0.0008-0.0020 in)
Ring end gap (Top):0.300-0.450 mm (0.0118-0.0177 in)
Ring end gap (Second):0.300-0.450 mm (0.0118-0.0177 in)
Ring end gap (Oil):0.250-0.400 mm (0.0098-0.0157 in)
Number of main bearings:3
Crankshaft main journal diameter:51.921-51.940 mm (2.0441-2.0449 in)
Crankpin journal diameter:43.959-43.975 mm (1.7307-1.7313 in)
Cylinder head
Valves:2, (4 valves in total)
Valve seat width (INTAKE):2.100 mm (0.080 in)
Valve seat width (EXHAUST):2.100 mm (0.080 in)
Value seat angle (INTAKE):45°
Value seat angle (EXHAUST):45°
Valveface angle (INTAKE):45°
Valveface angle (EXHAUST):45°
Valve steam diameter (INTAKE):7.960-7.975 mm (0.3134-0.3140 in)
Valve steam diameter (EXHAUST):7.960-7.975 mm (0.3134-0.3140 in)
Valve spring free length (INTAKE):42.0 mm (1.6535 in)
Valve spring free length (EXHAUST):42.0 mm (1.6535 in)
Camshaft journal diameter :39.935-39.950 mm (1.5722-1.5728 in)

Tightening torque

Tightening torque specs
Cylinder head screw:75.0-78.0 Nm (7.65-7.80 kgf·m, 55.3-58.0 lb·ft)
Connecting rod screw:37.0-41.0 Nm (3.8-4.2 kgf·m; 27.3-30.3 lb·ft)
Flywheel screw:54.0-58.0 Nm (5.5-5.9 kgf·m; 39.9-42.8 lb·ft)
Idle gear shaft screws:32.4-37.3 Nm (3.3-3.8 kgf·m; 23.9-27.5 lb·ft)
Bearing case cover mounting screw:30.0-34.0 Nm (3.0-3.4 kgf·m; 22.0-25.0 lb·ft)

Service Data

Maximum speed:2,950 rpm
Idle speed:600-650 rpm
Valve clearance
Intake valve clearance:0.18-0.22 mm (0.0071-0.0087 in)
Exhaust valve clearance:0.18-0.22 mm (0.0071-0.0087 in)
Oil system
Lubrication system:Forced lubrication
Oil type:DS or DM
Recommended oil:SAE 80
Oil capacity:3.8 liters (4.02 US.qts, 3.34 Imp. qts)
Fuel system
Injection timing:25° B.T.D.C.
Fuel injection pressure13.73-14.71 MPa (140-150 kgf/cm2, 1991-2133 psi)
Cooling system
Type:Pressurized radiator, forced circulation with water pump
Coolant capacity:5.3 liters (5.6 US.qts, 4.7 Imp. qts)
Electrical system
Battery:12V, 65AH or equivalent


Manufacturer or BrandModels
Author: Sergei Wers
About: Co-founder and CEO of a multi-brand auto repair shop (engine repair, chassis repair, body repair and painting) for over 15 years. I have been developing internet sites with technical specifications for more than seven years.

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We try to use official documentation and verify the published data, but errors may occur. In addition, specifications of machinery and equipment may vary depending on markets and modifications. We do not recommend the use of this data for spare parts or repairs. Use official service manuals or parts catalogs for your product.

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