Onan B43G

Onan B43GThe Onan B43G is a 0.7 L (710 cc, 43.33 cu·in) two cylinders natural aspirated 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 66.55 mm (2.62 in), respectively. The compression ratio rating is 6.5:1.

This engine produced 18.2 PS (13.4 kW; 18.0 HP) at 3,600 rpm of horsepower and 43.0 N·m (4.4 kg·m, 31.7 ft·lb) of torque.

The Onan B43G features:

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

General information

Engine Specifications
Engine modelB43G
Engine type4-stroke, L-head,
Displacement710 cm3, (43.33 cu·in)
Max. horsepower18.2 PS (13.4 kW; 18.0 HP) at 3,600 rpm
Max. torque43.0 N·m (4.4 kg·m, 31.7 ft·lb)
Cooling systemForced air
Air cleaner
Lubricating systemForced lubrication
Ignition systemAutomotive type battery ignition system
Fuel systemCarburetor
Fuel usedUnleaded gasoline (octane number 86 or higher)
Starting systemElectric starter
Stoping systemIgnition primary circuit ground
Dimensions (L x W X H)
Dry weight

Cylinder Block and Head

Cylinder block
Compression ratio:6.5:1
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
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):29.570—29.720 mm (1.1640—1.1700 in.)
Camshaft journal diameter:29.440—29.590 mm (1.1590—1.1650 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: With oil filter: 1.7 L (1.8 US. qt, 1.5 Imp. qt.)
Without oil filter:1.4 L (1.48 US. qt, 1.23 Imp. qt.)
Fuel system
Ignition system
Type:Automotive type battery ignition system
Ignition timing:16° B.T.D.C.
Spark plug:NGK BPR5EF, Champion RS14YC
Spark plug gap:0.640 mm (0.0252 in)
Ignition coil air gap0.410 mm (0.0161 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.

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