Onan B48G

Onan B48GThe Onan B48G is a 0.8 L (782 cc, 47.7 cu·in) natural aspirated two-cylinders four-stroke air-cooled internal combustion small gasoline engine with a horizontal shaft, for general-purpose applications.

Cylinder bore and piston stroke are 82.55 mm (3.25 in) and 73.00 mm (2.87 in), respectively. The compression ratio rating is 7.0:1.

This engine produced 20.3 PS (14.9 kW; 20.0 HP) at 3,600 rpm of horsepower and 43.0 N·m (4.4 kg·m, 31.7 ft·lb) of torque.

The Onan B48G features:

  • L-head design
  • Automotive type battery ignition system ignition system
  • Carburetor fuel system
  • Forced lubrication system
  • Air-cooling system
  • Electric starter

General information

Engine Specifications
Engine model B48G
Engine type 4-stroke, L-head, two-cylinders
Displacement 782 cm3, (47.72 cu·in)
Max. horsepower 20.3 PS (14.9 kW; 20 HP) at 3,600 rpm
Max. torque 43.0 N·m (4.4 kg·m, 31.7 ft·lb)
Cooling system Forced air
Air cleaner
Lubricating system Forced lubrication
Ignition system Automotive type battery ignition system
Fuel system Carburetor
Fuel used Unleaded gasoline (octane number 86 or higher)
Starting system Electric starter
Dimensions (L x W X H)
Dry weight

Cylinder Block and Head

Cylinder block
Compression ratio: 7.0:1
Cylinder bore: 82.55 mm (3.25 in)
Piston stroke: 73.00 mm (2.87 in)
Cylinder internal diameter (standard): 82.530-82.550 mm (3.2492-3.25 in)
Piston skirt outer diameter (standard): 82.42-82.44 mm (3.2449-3.2457 in)
Number of piston rings (compression / oil): 2/1
Connecting rod small end diameter (standard): 17.470-17.480 mm (0.6878-0.6882 in)
Piston pin diameter: 17.463-17.468 mm (0.6875-0.6877 in)
Ring end gap (Top): 0.250-0.510 mm (0.0098-0.0201 in)
Ring end gap (Second): 0.250-0.510 mm (0.0098-0.0201 in)
Number of main bearings: 2
Crankshaft main journal diameter: 50.780-50.800 mm (1.9992-2 in)
Crankpin journal diameter: 41.280-41.300 mm (1.6252-1.626 in)
Crankshaft center distance: 36.5 mm (1.435 in)
Cylinder head
Valve arrangement: L-head, gear driven
Valves: 2 (4 valves in total)
Valve steam diameter (INTAKE): 8.700-8.710 mm (0.3425-0.3429 in)
Valve steam diameter (EXHAUST): 8.660-8.670 mm (0.3409-0.3413 in)
Valve spring free length (INTAKE): 42.210 mm (1.6618 in)
Valve spring free length (EXHAUST): 42.210 mm (1.6618 in)
Camshaft lobe height (INTAKE): 29.570-29.720 mm (1.1642-1.1701 in)
Camshaft lobe height (EXHAUST): 29.440-29.590 mm (1.1591-1.165 in)
Camshaft journal diameter : 34.900-34.910 mm (1.374-1.3744 in)

Service Data

Cylinder compression: 517-793 kPa (75 to 115 psi)
Valve clearance
Intake valve clearance (COLD): 0.130 mm (0.0051 in)
Exhaust valve clearance (COLD): 0.330 mm (0.013 in)
Oil system
Lubrication system: Forced lubrication
Oil type: SF, SF/CC, or SF/CD
Recommended oil: SAE 10W-30
Oil capacity: Without oil filter: 1.4 L (1.48 US. qt, 1.23 Imp. qt.)
With oil filter: 1.7 L (1.8 US. qt, 1.5 Imp. qt.)
Fuel system
Type: Carburetor
Ignition system
Type: Automotive type battery ignition system
Ignition timing: Spec A&B: 20° B.T.D.C.
Spec C: 16° B.T.D.C.
Spark plug: NGK BPR5EF, Champion RS14YC
Spark plug gap: 0.640 mm (0.0252 in)
Ignition coil air gap Spec A&B: 0.530 mm (0.020 in)
Spec C: 0.410 mm (0.016 in)

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