Honda GX640 Specifications
| Engine Model: Honda GX640 |
| Engine Type: 4-cycle two-cylinder OHV liquid-cooled gasoline |
| Total Displacement: 38.7 cu.in (635 cc) |
| Rated Engine Power: 20 Hp (14.7 kW) at 3600 rpm |
| Carburetor Type: Horizontal with butterfly valve |
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Engine Model .............. Honda GX640
Engine Type .............. 4-cycle overhead valve liquid-cooled gasoline engine
Number of Cylinders .............. 2
Displacement, cu.in (cc) .............. 38.7 (635)
Cylinder Bore, in (mm) .............. 3.00 (76.0)
Piston Stroke, in (mm) .............. 2.77 (70.0)
Rated Engine Power, hp (kW) .............. 20.0 (14.7)
Rated Engine Speed, rpm .............. 3600
Maximum Torque, Nm (ft-lbs) .............. 46.1 (34.0)
Torque Speed, rpm .............. 2500
Compression Ratio .............. 8.0:1
Valve Arrangement .............. OHV
PTO Shaft Rotation .............. Counterclockwise (from PTO side)
Lubrication System .............. Forced oil trochoid pump
Air Cleaner .............. Dual element
Cooling System .............. Liquid-cooled
Coolant Capacity, qts (L) .............. 4.12 (3.90)
Ignition System .............. CDI
Starting System .............. Electric starter
Fuel System Type .............. Carburetor
Carburetor Type .............. Horizontal, butterfly valve
Governor Type .............. Mechanical
Fuel Type .............. Gasoline (86 or higher)
Overall Length, in (mm) .............. 17.7 (449)
Overall Width, in (mm) .............. 16.5 (420)
Overall Height, in (mm) .............. 21.7 (551)
Dry Weight, lbs (kg) .............. 110 (50.0)
Operating Weight, lbs (kg) .............. 115 (52.0)
Cylinder Bore Inside Diameter (Std), in (mm) .............. 2.9921-2.9927 (76.000-76.015)
Cylinder Bore Inside Diameter (Wear Limit), in (mm) .............. 2.996 (76.100)
Connecting Rod Small End Inside Diameter (Std), in (mm) .............. 0.7483-0.7487 (19.006-19.018)
Connecting Rod Small End Inside Diameter (Wear Limit), in (mm) .............. 0.7506 (19.066)
Connecting Rod Big End Oil Clearance, in (mm) .............. 0.0008-0.0015 (0.020-0.038)
Crankshaft Main Journal Outside Diameter (Std), in (mm) .............. 1.5739-1.5748 (39.976-40.000)
Crankshaft Main Journal Outside Diameter (Wear Limit), in (mm) .............. 1.572 (39.930)
Crank Pin Outside Diameter (Std), in (mm) .............. 1.4951-1.4961 (37.976-38.000)
Crank Pin Outside Diameter (Wear Limit), in (mm) .............. 1.493 (37.930)
Crankshaft Main Bearing Oil Clearance, in (mm) .............. 0.0008-0.0015 (0.020-0.038)
Crankshaft Side Clearance, in (mm) .............. 0.004-0.014 (0.10-0.36)
Camshaft Journal Outside Diameter (Std), in (mm) .............. 1.1007-1.1016 (27.959-27.980)
Camshaft Journal Outside Diameter (Wear Limit), in (mm) .............. 1.098 (27.900)
Cylinder Head (Max Out of Flatness), in (mm) .............. 0.004 (0.10)
Intake Valve Clearance, in (mm) .............. 0.005±0.001 (0.12±0.02)
Exhaust Valve Clearance, in (mm) .............. 0.008±0.001 (0.20±0.02)
Intake Valve Stem Outside Diameter (Std), in (mm) .............. 0.1961-0.1965 (4.980-4.990)
Intake Valve Stem Outside Diameter (Wear Limit), in (mm) .............. 0.191 (4.85)
Exhaust Valve Stem Outside Diameter (Std), in (mm) .............. 0.1953-0.1957 (4.960-4.970)
Exhaust Valve Stem Outside Diameter (Wear Limit), in (mm) .............. 0.190 (4.83)
Valve Guide Inside Diameter (Intake/Exhaust), in (mm) .............. 0.1969-0.1973 (5.000-5.012)
Intake Valve Guide To Stem Clearance, in (mm) .............. 0.0004-0.0013 (0.010-0.032)
Exhaust Valve Guide To Stem Clearance, in (mm) .............. 0.0012-0.0020 (0.030-0.052)
Valve Seat Width (Intake/Exhaust), in (mm) .............. 0.037-0.049 (0.95-1.25)
Valve Spring Free Length, in (mm) .............. 1.521 (38.64)
Cam Height (Std), in (mm) .............. 1.207-1.219 (30.67-30.95)
Cam Height (Wear Limit), in (mm) .............. 1.209-1.220 (30.71-30.99)
Piston Pin Bore Inside Diameter (Std), in (mm) .............. 0.7481-0.7483 (19.002-19.008)
Piston Pin Bore Inside Diameter (Wear Limit), in (mm) .............. 0.7502 (19.055)
Piston Skirt Outside Diameter, in (mm) .............. 2.992 (75.990)
Piston to Cylinder Bore Clearance, in (mm) .............. 0.0004-0.0018 (0.010-0.045)
Piston Pin Outside Diameter (Std), in (mm) .............. 0.7478-0.7480 (18.994-19.000)
Piston Pin Outside Diameter (Wear Limit), in (mm) .............. 0.7462 (18.954)
Top Ring Width, in (mm) .............. 0.0463-0.0469 (1.175-1.190)
Second Ring Width, in (mm) .............. 0.0463-0.0469 (1.175-1.190)
Top Ring Groove Side Clearance, in (mm) .............. 0.001-0.002 (0.03-0.06)
Second Ring Groove Side Clearance, in (mm) .............. 0.001-0.002 (0.03-0.06)
Top Ring End Gap, in (mm) .............. 0.010-0.016 (0.25-0.40)
Second Ring End Gap, in (mm) .............. 0.010-0.016 (0.25-0.40)
Ring End Gap (Wear Limit), in (mm) .............. 0.02 (0.60)
Cylinder Bore Inside Diameter (Max), in (mm) .............. 2.996 (76.100)
Cylinder Compression, psi (kPa) .............. 57-100 (392-686)
Cylinder Head (Max Out of Flatness), in (mm) .............. 0.004 (0.10)
Intake Valve Clearance, in (mm) .............. 0.004-0.006 (0.10-0.14)
Exhaust Valve Clearance, in (mm) .............. 0.007-0.009 (0.18-0.22)
Engine Oil Type (Summer) .............. SAE 10W-30
Engine Oil Type (Winter) .............. SAE 5W-30
API Service Classifications .............. SG, SF or CC, CD
Oil Capacity (with Filter), qts (L) .............. 2.43 (2.30)
Spark Plug Type .............. NGK BPR5ES or Denso W16EPR-U11
Spark Plug Gap, in (mm) .............. 0.039-0.043 (1.0-1.1)
Ignition Timing, deg .............. 22 BTDC
Oil Filter Part Number .............. 15400-PFB-014
Air Filter Part Number .............. 17210-ZG8-000
Main Jet .............. #98
Idle Fuel .............. 1-1/2 turns out
Float Height, in (mm) .............. 0.55 (14.0)
Low Idle Speed, rpm .............. 1400±100
High Idle Speed, rpm .............. 3750±100
Check Engine Oil Level .............. Every 10 hours
Clean Air Filter Element .............. Every 50 hours
Change Engine Oil .............. Every 100 hours
Check and Adjust Spark Plug .............. Every 100 hours
Clean Fuel Filter .............. Every 100 hours
Clean Radiator Core .............. Every 100 hours
Replace Engine Oil Filter .............. Every 200 hours
Check and Adjust Idle Speed .............. Every 300 hours
Check Carburetor Adjustments .............. Every 300 hours
Replace Spark Plug .............. Every 300 hours
Replace Fuel Filter .............. Every 300 hours
Replace Air Filter Element .............. Every 300 hours
Check and Adjust Valve Clearance .............. Every 300 hours
Clean Combustion Chamber .............. Every 500 hours
Clean Fuel Line .............. Every 500 hours
Change Radiator Coolant .............. Every 500 hours
Oil Drain Bolt (M12x1.25), Nm (ft-lb) .............. 34 (25)
Oil Filter (M20x1.0), Nm (ft-lb) .............. 8 (6)
Air Cleaner Case Nut (M6x1.0), Nm (ft-lb) .............. 9 (7)
Flywheel Bolt (M10x1.25), Nm (ft-lb) .............. 71 (51)
Governor Slider Shaft (M8x1.25), Nm (ft-lb) .............. 43 (31)
Cooling Fan Bracket Bolt (M6x1.0), Nm (ft-lb) .............. 14 (10)
Cooling Fan Pulley Bolt (M6x1.0), Nm (ft-lb) .............. 11 (8)
Cooling Fan Bolt (M6x1.0), Nm (ft-lb) .............. 11 (8)
Tension Pulley Bolt (M6x1.0), Nm (ft-lb) .............. 11 (8)
Timing Belt Rear Cover Bolt (M6x1.0), Nm (ft-lb) .............. 13 (9)
Timng Belt Driven Pulley Bolt (M8x1.25), Nm (ft-lb) .............. 30 (22)
Timing Belt Cover Bolt (M6x1.0), Nm (ft-lb) .............. 8 (6)
Cylinder Head Bolt (M10x1.25), Nm (ft-lb) .............. 55 (40)
Spark Plug, Nm (ft-lb) .............. 20 (14)
Crankcase Bolt (M8x1.25), Nm (ft-lb) .............. 22 (16)
Connection Rod Cap Nut (M8x0.75), Nm (ft-lb) .............. 29 (21)
PTO Shaft Bolt (M8x1.25), Nm (ft-lb) .............. 32 (23)
Thermo Switch (M16x1.5), Nm (ft-lb) .............. 12 (9)
Oil Pressure Switch Terminal Screw (M4x0.7), Nm (ft-lb) .............. 2.3 (1.7)
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