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 modelB43E
Engine type4-stroke, L-head, flat
Displacement710 cm3, (43.33 cu·in)
Max. horsepower16.2 PS (11.9 kW; 16.0 HP) at 3,600 rpm
Max. torque44.0 N·m (4.5 kg·m, 32.4 ft·lb)
Cooling systemAir-cooled
Air cleaner
Lubricating systemForced lubrication
Ignition system
Fuel systemCarburetor
Fuel consumption
Fuel usedUnleaded gasoline (octane number 86 or higher)
Starting systemElectric 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
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 gap0.410 mm (0.01610.0161 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.

1 Comment

  1. That for the information. Do you have a list of the torque spec for heads and intake? Planning on changing gaskets.

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