Onan P218G

Onan P218GThe Onan P218G is a 782 cc, (47.7 cu·in) natural aspirated two-cylinders four-stroke air-cooled internal combustion small gasoline engine with a horizontal shaft, manufactured by Onan for general-purpose applications.

The cylinder bore is 82.55 mm (3.25 in) and the piston stroke is 73.00 mm (2.87 in). The compression ratio rating is 7.0:1.

The Onan P218G engine produced 18.2 PS (13.4 kW; 18.0 HP) at 3,600 rpm of maximum output power.

The Onan P218G features:

  • L-haed design
  • Electronic battery ignition system
  • Carburetor with fixed main jet
  • Centrifugal governor
  • Full pressure with oil filter lubrication system
  • Forced air cooling system
  • Electric starter 12V

General information

Engine Specifications
Engine modelP218G Performer 18
Engine type4-stroke, L-head, two-cylinders
Displacement782 cm3, (47.7 cu·in)
Max. horsepower18.2 PS (13.4 kW; 18.0 HP) at 3,600 rpm
Cooling systemForced air
Lubricating systemFull pressure with oil filter
Ignition systemElectronic battery
Fuel systemCarburetor with fixed main jet
Fuel usedUnleaded gasoline (octane number 86 or higher)
Starting systemElectric starter 12V
Stoping systemIgnition primary circuit ground
GovernorCentrifugal governor
Charging systemFlywheel alternator
PTO shaft rotationCounterclockwise (from PTO shaft side)

Cylinder Block and Head

Cylinder block
Compression ratio:7.0:1
Cylinder bore:82.55 mm (3.25 in)
Piston stroke:66.55 mm (2.62 in)
Cylinder internal diameter (standard):82.530-82.530 mm (3.2490-3.2500 in)
Number of piston rings (compression / oil):2/1
Connecting rod big end diameter (standard):41.360-41.350 mm (1.6283-1.6279 in)
Connecting rod small end diameter (standard):17.470-17.480 mm (0.6878-0.6882 in)
Piston pin diameter:17.470-17.480 mm (0.6878-0.6882 in)
Ring Groove Clearance (Top):0.076-0.203 mm (0.003-0.008 in)
Ring End Gap in Cylinder Clearance:0.254-0.508 mm (0.010-0.020 in)
Crankshaft Main Bearing Journal Diameter:50.800-50.780 mm (2.0000-1.9992 in)
Crankpin journal diameter:41.300-41.280 mm (1.6260-1.6252 in)
Crankshaft center distance:33.275 mm (1.31 in)
Cylinder head
Valve arrangement:L-head, gear driven
Valves:4,(2 valves in total)
Valve steam diameter (INTAKE):7.099-7.112 mm (0.2795-0.2800 in)
Valve steam diameter (EXHAUST):7.061-7.074 mm (0.278-0.2785 in)
Valve Clearance Stem-to-Guide (INTAKE):0.025-0.064 mm (0.0010-0.0025 in)
Valve Clearance Stem-to-Guide (EXHAUST):0.051-0.089 mm (0.0020-0.0035 in)
Valve spring free length (INTAKE):40.64 mm (1.6 in)
Valve spring free length (EXHAUST):40.64 mm (1.6 in)
Camshaft lobe height (INTAKE):28.88 mm (1.137 in)
Camshaft lobe height (EXHAUST):29.39 mm (1.1571 in)

Tightening Torque

Tightening torque specs
Gearcase cover11-14 Nm (8-10 ft-lb)
Cylinder head bolts (asbestos gasket)22-24 Nm (16-18 ft-lb)
Cylinder head bolts (graphoil gasket)19-22 Nm (14-16 ft-lb)
Rear bearing plate screws34-37 Nm (25-27 ft-lb)
Starter mounting bolts33-35 Nm (24-26 ft-lb)
Connecting rod bolt19 Nm (14 ft-lb)
Flywheel cap screw67-75 Nm (50-55 ft-lb)
Other 1/4″ cylinder block stud and nuts10-12 Nm (7-9 ft-lb)
Other 5/16″ cylinder block stud and nuts11-14 Nm (8-10 ft-lb)
Oil base24-31 Nm (18-23 ft-lb)
Intake manifold mounting screws8-14 Nm (6-10 ft-lb)
Oil pump10-12 Nm (7-9 ft-lb)
Valve cover1-3 Nm (1-2 ft-lb)
Exhaust manifold mounting screws12-15 Nm (9-11 ft-lb)

Service Data

Cylinder compression:517-793 kPa; 75-115 PSI
Valve clearance
Intake valve clearance:0.13 mm (0.0051 in)
Exhaust valve clearance:0.33 mm (0.0130 in)
Oil system
Lubrication system:Full pressure with oil filter
Oil type:API SF, SF/CC, or SF/CD
Recommended oil:SAE 5W-30, 10W-30, 30W, 40W
Oil capacity: Standard base (w/o oil filter): 1.4 L (1.5 US. qt, 1.2 Imp. qt.)
High capacity base (w/o oil filter): 2.6 L (2.75 US. qt, 2.3 Imp. qt.)
Oil filter: 0.3 L (0.32 US. qt, 0.26 Imp. qt.)
Fuel system
Type:Carburetor with fixed main jet
Pilot screw opening:1-1/4 turns out
Fuel pump type:Pulse
Ignition system
Type:Electronic battery ignition system
Ignition timing:20° B.T.D.C.
Spark plug:NGK: BPR5EFS; Champion: RS14YC
Spark plug gap:0.64 mm (0.0252 in)
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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