________________________________________________________________________________

Onan B48G Engine

General Technical Data

Onan B48G Engine Specifications

Engine Model .......... Onan B48G
Engine Type .......... Gasoline, 2-cylinder 4-valve
Number of cylinders .......... Two
Bore, mm (in.) .......... 82.6 (3.25)
Stroke, mm (in.) .......... 73.0 (2.88)
Total displacement, cm3 (cu. in.) .......... 782 (47.7)
Gross power, kw (hp) .......... 14.9 (20.0)
Maximum speed, rpm .......... 3500
Idle speed, rpm .......... 1350
Crankshaft Alignment .......... Horizontal
Cylinder Material .......... Aluminum
Compression ratio .......... 7.0:1
Spark Plugs .......... NGK BPR5EFS / Champion RS14YC

Fuel System

Fuel System Type .......... Carburetor
Carburetor Model .......... Nikki
Fuel Gauge .......... Standard
Fuel Reserve System .......... Standard
Fuel Tank Capacity, L (gal) .......... 25 (6.5)
Fuel Pump Location .......... Engine
Fuel Pump Type .......... Pulse
Fuel Delivery .......... Fixed Jet Carburetor

Lubricating System

Lubricating system Type .......... Full Pressure with filter
Crankcase Capacity (w/o Filter), L (qt) .......... 1,4 (1,5)
Oil filter .......... Replaceable

Electrical System

Ignition .......... Electronic
Type of Starter .......... 12 Volts, Solenoid
Charging System .......... 20 amp Stator
Battery Type .......... BCI Group 22F
Battery Voltage .......... 12V

Onan B48G Maintenance Data

Fuel Type (min. octane) .......... 85 Octane Unleaded
Engine oil type .......... SAE 10W-40/5W-30
Engine oil capacity, L (qts) .......... 1.4 (1.5)
Oil filter change interval .......... Every 100 hours
Oil change interval .......... Every 100 hours
Fuel filter change interval .......... Every 100 hours

Onan B48G Service Specifications

Cylinder Block

Cylinder Bore Honed Diameter, in (mm) .......... 3.2490 (82.53) - 3.2500 (82.55)
Main Bearing Inside Diameter (Without bearing), in (mm) .......... 2.187 (55.55) - 2.188 (55.58)
Main Bearing inside Diameter (Installed), in (mm) .......... 2.0015 (50.84) - 2.004 (50.90)
Camshaft Bearing Bore (Bearing installed), in (mm) .......... 1.3760 (34.95) - 1.3770 (34.98)
Tappet Body Diameter, in (mm) .......... 0.7475 (18.99) - 0.7480 (19.00)
Tappet Bore Diameter, in (mm) .......... 0.7500 (19.05) - 0.7515 (19.09)
Tappet Clearance in Bore, in (mm) .......... 0.0015 (0.038) - 0.003 (0.076)
Crankshaft Main Bearing Journal Diameter, in (mm) .......... 1.9992 (50.78) - 2.0000 (50.80)
Crankshaft Main Bearing Clearance, in (mm) .......... 0.0025 (0.064) - 0.0038 (0.097)
Connecting Rod Journal Diameter, in (mm) .......... 1.6252 (41.28) - 1.6260 (41.30)
Crankshaft End Play, in (mm) .......... 0.006 (0.15) - 0.012 (0.30)
Connecting Rod Large Bore Diameter, in (mm) .......... 1.6280 (41.35) - 1.6285 (41.36)
Connecting Rod Side Clearance, in (mm) .......... 0.0020 (0.051) - 0.0160 (0.406)
Piston Pin Bushing Bore (Finished bore), in (mm) .......... 0.6879 (17.47) - 0.6882 (17.48)
Bearing to Crankshaft Clearance (Aluminum Rod), in (mm) .......... 0.0020 (0.051) - 0.0033 (0.084)
Camshaft Bearing Journal Diameter, in (mm) .......... 1.3740 (34.90) - 1.3745 (34.91)
Camshaft Bearing Clearance, in (mm) .......... 0.0015 (0.038) - 0.0030 (0.076)
Camshaft End Play, in (mm) .......... 0.0030 (0.076)
Camshaft Lift (Intake), in (mm) .......... 0.286 (7.26) - 0.295 (7.49)
Camshaft Lift (Exhaust) .......... 0.291 (7.39) - 0.299 (7.59)

Piston and Piston Rings

Piston Clearance in Cylinder, in (mm) .......... 0.0033 (0.084) - 0.0053 (0.135)
Piston Pin Bore, in (mm) .......... 0.68774 (17.47) - 0.68814 (17.48)
Top 1 Compression Ring Groove Width, in (mm) .......... 0.080 (2.032) - 0.081 (2.057)
Top 2 Compression Ring Groove Width, in (mm) .......... 0.080 (2.032) - 0.081 (2.057)
Oil Control Ring Groove Width, in (mm) .......... 0.188 (4.775) - 0.189 (4.801)
Piston Pin Clearance in Piston, in (mm) .......... 0.00004 (0.001) - 0.00064 (0.016)
Piston Pin Clearance in Connecting Rod, in (mm) .......... 0.0002 (0.005) - 0.0007 (0.018)
Piston Pin Diameter, in (mm) .......... 0.6875 (17.46) - 0.6877 (17.47)
Top Ring Groove Clearance, in (mm) .......... 0.003 (0.076) - 0.008 (0.203)
Ring End Gap in Cylinder Clearance, in (mm) .......... 0.010 (0.254) - 0.020 (0.508)

Cylinder Head

Intake Valve Stem Diameter, in (mm) .......... 0.3425 (8.70) - 0.3430 (8.71)
Exhaust Valve Stem Diameter, in (mm) .......... 0.3410 (8.661) - 0.3415 (8.674)
Intake Valve Clearance (Stem to Guide), in (mm) .......... 0.0010 (0.025) - 0.0025 (0.064)
Exhaust Valve Clearance (Stem to Guide), in (mm) .......... 0.0025 (0.064) - 0.040 (0.102)
Intake/Exhaust Valve Face Angle, degrees .......... 44
Intake Valve Seat Cylinder Bore Diameter, in (mm) .......... 1.4395 (36.56) - 1.4405 (36.59)
Exhaust Valve Seat Cylinder Head Bore Diameter, in (mm) .......... 1.189 (30.20) - 1.190 (30.23)
Intake Valve Seat Outside Diameter, in (mm) .......... 1.470 (37.34) - 1.471 (37.36)
Exhaust Valve Seat Outside Diameter, in (mm) .......... 1.192 (30.28) - 1.193 (30.30)
Intake/Exhaust Valve Seat Width, in (mm) .......... 0.031 (0.787) - 0.047 (1.194)
Intake/Exhaust Valve Seat Angle, degrees .......... 45
Valve Guide Inside Diameter, in (mm) .......... 0.344 (8.74) - 0.345 (8.76)
Valve Spring Free Length, in (mm) .......... 1.662 (42.21)
Valve Open, in (mm) .......... 1.125 (28.58)
Valve Closed , in (mm) .......... 1.375 (34.93)
Spring Load / 1.375 inch (Valve Closed), lb (kg) .......... 38 (17) - 42 (19)
Spring Load / 1.125 inch (Valve Open), lb (kg) .......... 71 (32) - 79 (36)

Tightening Torque Specs

Gearcase Cover, ft-lb (Nm) .......... 8-10 (11-14)
Cylinder Head Bolts (Asbestos Gasket), ft-lb (Nm) .......... 16-18 (22-24)
Cylinder Head Bolts (Graphoil Gasket) 14-16 (19-22)
Rear Bearing Plate Screws 25-27 (34-37)
Starter Mounting Bolts, ft-lb (Nm) .......... 24-26 (33-35)
Connecting Rod Bolt, ft-lb (Nm) .......... 14 (19)
Flywheel Cap Screw, ft-lb (Nm) .......... 50-55 (67-75)
Other 1/4" Cylinder Block Stud and Nuts, ft-lb (Nm) .......... 7-9 (10-12)
Other 5/16" Cylinder Block Stud and Nuts, ft-lb (Nm) .......... 8-10 (11-14)
Oil Base, ft-lb (Nm) .......... 18-23 (24-31)
Intake Manifold Mounting Screws, ft-lb (Nm) .......... 6-10 (8-14)
Oil Pump, ft-lb (Nm) .......... 7-9 (10-12)
Valve Cover, ft-lb (Nm) .......... 1-2 (1-3)
Exhaust Manifold Mounting Screws, ft-lb (Nm) .......... 9-11 (12-15)