Onan B48G

Onan B48GThe Onan B48G is a 782 cc (47.7 cu-in) two cylinder air-cooled four-stroke internal combustion small gasoline engine with horizontal shaft manufactured by Onan for general-purpose applications.

The B48G engine has an L-head design with two flat cylinders; a carburetor fuel system, an automotive-type battery ignition system, and an electric starter.

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 B48G 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.

General information

Engine Specifications
Model Onan B48G
Type 4-stroke, L-head, flat
Displacement 782 cm3 (47.7 cu-in)
Max. horsepower 20.0 HP (14.9 kW) at 3,600 rpm
Max. torque 43.0 N·m (4.4 kg·m, 31.7 ft·lb)
Cooling system Forced-air
Ignition system Automotive-type battery ignition system
Lubricating system Forced lubrication
Starting system Electric starter
PTO shaft rotation Clockwise (viewed from flywhee)

Cylinder Block and Head

Cylinder block
Compression ratio: 7.0:1
Bore x Stroke 82.55 X 73.00 mm (3.25 x 2.87 in)
Sleeve internal diameter 82.530-82.550 mm (3.2492-3.25 in)
Piston skirt outer diameter 82.42-82.44 mm (3.2449-3.2457 in)
Ring end gap Top/Second 0.250-0.510 mm (0.0098-0.0201 in)
Connecting rod small end ID 17.470-17.480 mm (0.6878-0.6882 in)
Piston pin outer diameter 17.463-17.468 mm (0.6875-0.6877 in)
Crankpin diameter 41.280-41.300 mm (1.6252-1.626 in)
Crankshaft main journal diameter 50.780-50.800 mm (1.9992-2 in)
Cylinder Head
Valve Arrangement: L-haed
Valves: 4 (2 per cylinder)
Stem outer diameter (standard): INTAKE 8.700-8.710 mm (0.3425-0.3429 in)
EXHAUST 8.660-8.670 mm (0.3409-0.3413 in)
Valve spring free length: 42.210 mm (1.6618 in)
Camshaft journal diameter: 34.900-34.910 mm (1.374-1.3744 in)
Lobe height: INTAKE 29.570—29.720 mm (1.164—1.170 in)
EXHAUST 29.440—29.590 mm (1.159—1.165 in)

Service Information

Maximum speed 3,600
Cylinder compression 517-793 kPa (75 to 115 psi)
Valve clearance
Intake valve clearance 0.130 mm (0.0051 in)
Exhaust valve clearance 0.330 mm (0.013 in)
Oil system
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.)
Ignition system
Ignition timing Spec A&B: 20° B.T.D.C.
Spec A&B: 16° B.T.D.C.
Spark plug NGK BPR5EF, Champion RS14YC
Spark plug gap 0.640 mm (0.0252 in)
Breaker point gap Spec A&B: 0.530 mm (0.020 in)
Spec C: 0.410 mm (0.016 in)
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