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
ModelOnan B48G
Type4-stroke, L-head, flat
Displacement782 cm3 (47.7 cu-in)
Max. horsepower20.0 HP (14.9 kW) at 3,600 rpm
Max. torque43.0 N·m (4.4 kg·m, 31.7 ft·lb)
Cooling systemForced-air
Ignition systemAutomotive-type battery ignition system
Lubricating systemForced lubrication
Starting systemElectric starter
PTO shaft rotationClockwise (viewed from flywhee)

Cylinder Block and Head

Cylinder block
Compression ratio:7.0:1
Bore x Stroke82.55 X 73.00 mm (3.25 x 2.87 in)
Sleeve internal diameter82.530-82.550 mm (3.2492-3.25 in)
Piston skirt outer diameter82.42-82.44 mm (3.2449-3.2457 in)
Ring end gapTop/Second0.250-0.510 mm (0.0098-0.0201 in)
Connecting rod small end ID17.470-17.480 mm (0.6878-0.6882 in)
Piston pin outer diameter17.463-17.468 mm (0.6875-0.6877 in)
Crankpin diameter41.280-41.300 mm (1.6252-1.626 in)
Crankshaft main journal diameter50.780-50.800 mm (1.9992-2 in)
Cylinder Head
Valve Arrangement:L-haed
Valves:4 (2 per cylinder)
Stem outer diameter (standard):INTAKE8.700-8.710 mm (0.3425-0.3429 in)
EXHAUST8.660-8.670 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:INTAKE29.570—29.720 mm (1.164—1.170 in)
EXHAUST29.440—29.590 mm (1.159—1.165 in)

Service Information

Maximum speed3,600
Cylinder compression517-793 kPa (75 to 115 psi)
Valve clearance
Intake valve clearance0.130 mm (0.0051 in)
Exhaust valve clearance0.330 mm (0.013 in)
Oil system
Recommended oilSAE 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 C: 16° B.T.D.C.
Spark plugNGK BPR5EF, Champion RS14YC
Spark plug gap0.640 mm (0.0252 in)
Breaker point gap Spec A&B: 0.530 mm (0.020 in)
Spec C: 0.410 mm (0.016 in)
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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