Onan B43E

Onan B43EThe Onan B43E is a 0.7 L (710 cc, 43.33 cu·in) natural aspirated four-stroke air-cooled internal combustion small gasoline engine with a horizontal shaft, for general-purpose applications.

The cylinder bore is 82.55 mm (3.25 in) and the piston stroke is 66.55 mm (2.62 in). The compression ratio rating is 6.2:1.

The B43E engine produced 16.2 PS (11.9 kW; 16.0 HP) at 3,600 rpm of maximum horsepower and 44.0 N·m (4.5 kg·m, 32.4 ft·lb) of maximum torque.

The Onan B43E features:

  • L-head design
  • Carburetor fuel system
  • Forced lubrication system
  • Air cooling system
  • Electric starter

General information

Engine Specifications
Engine model B43E
Engine type 4-stroke, L-head, flat
Displacement 710 cm3, (43.33 cu·in)
Max. horsepower 16.2 PS (11.9 kW; 16.0 HP) at 3,600 rpm
Max. torque 44.0 N·m (4.5 kg·m, 32.4 ft·lb)
Cooling system Air-cooled
Air cleaner
Lubricating system Forced lubrication
Ignition system
Fuel system Carburetor
Fuel consumption
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: 6.2:1
Cylinder bore: 82.55 mm (3.25 in)
Piston stroke: 66.55 mm (2.62 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: 33.275 mm (1.31 in)
Cylinder head
Valve arrangement: L-head, gear driven
Valves: 4 (2 per cylinder)
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): 28.370-28.470 mm (1.1169-1.1209 in)
Camshaft lobe height (EXHAUST): 28.370-28.470 mm (1.1169-1.1209 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
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
Ignition timing: 16° B.T.D.C.
Spark plug: NGK BPR5EF, Champion RS14YC
Spark plug gap: 0.640 mm (0.0252 in)
Breaker point gap 0.410 mm (0.01610.0161 in)

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