Briggs and Stratton 31E777

Briggs and Stratton 31e777The Briggs and Stratton 31E777 is a 501 cc, (30.6 cu·in) natural aspirated single-cylinder four-stroke air-cooled internal combustion small gasoline engine with a vertical shaft, manufactured by Briggs & Stratton for general-purpose applications.

A 90.6 mm (3.57 in) cylinder bore and 77.8 mm (3.06 in) piston stroke give the B&S 31E777 engine a total of 501 cc of displacement. This engine produced 16.2 PS (11.9 KW; 16.0 HP) at 3,600 rpm of horsepower.

The B&S 31E777 features:

  • Cast iron sleeve
  • OHV (overhead) design
  • Plain bearing
  • Electronic ignition system
  • Float type carburetor
  • Mechanical governor
  • Full pressure lubrication system
  • Forced air cooling system
  • Electric starter

General information

Engine Specifications
Engine model 31E777
Engine type 4-stroke, OHV, single-cylinder
Displacement 501 cm3, (30.6 cu·in)
Max. horsepower 16.2 PS (11.9 KW; 16.0 HP) at 3,600 rpm
Max. torque
Cooling system Forced air
Air cleaner Paper filter with a foam pre-cleaner
Lubricating system Full pressure lubrication system
Ignition system Electronic
Fuel system Float type carburetor
Fuel used Gasoline
Starting system Electric starter
Governor Mechanical governor
Dimensions (L x W X H)
Dry weight

Cylinder Block and Head

Cylinder block
Cylinder bore: 90.6 mm (3.57 in)
Piston stroke: 77.7 mm (3.06 in)
Cylinder internal diameter (standard): 90.500-90.600 mm (3.563-3.5669 in)
Number of piston rings (compression / oil): 2/1
Connecting rod small end diameter (standard): 20.330-20.370 mm (0.8004-0.802 in)
Piston pin diameter: 20.310-20.290 mm (0.7996-0.7988 in)
Side clearance (Top): 0.05-0.12 mm (0.002-0.0047 in)
Side clearance (Second): 0.05-0.12 mm (0.002-0.0047 in)
Side clearance (Oil): 0.05-0.12 mm (0.002-0.0047 in)
Ring end gap (Top): 0.150-0.230 mm (0.0059-0.0091 in)
Ring end gap (Second): 0.350-0.450 mm (0.0138-0.0177 in)
Ring end gap (Oil): 0.150-0.250 mm (0.0059-0.0098 in)
Crankshaft main journal diameter: 35.000 mm (1.378 in)
Crankpin journal diameter: 38.050 mm (1.498 in)
Crankshaft center distance: 38.9 mm (1.53 in)
Cylinder head
Valve arrangement: OHV
Valves: 2
Valve steam diameter (INTAKE): 5.920-5.970 mm (0.2331-0.235 in)
Valve steam diameter (EXHAUST): 5.920-5.970 mm (0.2331-0.235 in)
Camshaft lobe height (INTAKE): 31.490 mm (1.2398 in)
Camshaft lobe height (EXHAUST): 31.490 mm (1.2398 in)
Camshaft journal diameter: 12.670 mm (0.4988 in)

Tightening torque

Tightening torque specs
Air cleaner base 6.0 Nm; 4.4 ft·lb
Alternator 2.0 Nm; 1.5 ft·lb
Armature 3.0 Nm; 2.2 ft·lb
Blower housings 10.0 Nm; 7.4 ft·lb
Blower housing brackets 10.0 Nm; 7.4 ft·lb
Breather 3.0 Nm; 2.2 ft·lb
Carburetor to intake manifold 8.0 Nm; 5.9 ft·lb
Carburetor solenoid 5.0 Nm; 3.7 ft·lb
Connecting rod 17.0 Nm; 12.6 ft·lb
Control bracket 5.0 Nm; 3.7 ft·lb
Crankcase sump 25.0 Nm; 18.5 ft·lb
Cylinder head 25.0 Nm; 18.5 ft·lb
Cylinder shield 5.0 Nm; 3.7 ft·lb
Exhaust manifold / adapter 19.0 Nm; 14.0 ft·lb
Flywheel nut 135.0 Nm; 100.0 ft·lb
Flywheel fan 16.0 Nm; 11.9 ft·lb
Fuel pump 10.0 Nm; 7.4 ft·lb
Governor lever nut 5.0 Nm; 3.7 ft·lb
Intake manifold to cylinder head 10.0 Nm; 7.4 ft·lb
Muffler 10.0 Nm; 7.4 ft·lb
Oil drain plug 11.0 Nm; 8.1 ft·lb
Oil fill tube 10.0 Nm; 7.4 ft·lb
Oil pump cover 10.0 Nm; 7.4 ft·lb
Regulator / Rectifier 5.0 Nm; 3.7 ft·lb
Rewind starter 3.0 Nm; 2.2 ft·lb
Rocker ball set screw or nut 5.0 Nm; 3.7 ft·lb
Rocker cover 7.0 Nm; 5.2 ft·lb
Starter motor 16.0 Nm; 11.9 ft·lb

Service Data

Valve clearance
Intake valve clearance: 0.08-0.13 mm (0.003-0.005 in)
Exhaust valve clearance: 0.13-0.17 mm (0.005-0.007 in)
Oil type: SF, SG, SH, SJ or higher
Recommended oil: Summer: SAE 30, 10W-30
Winter: SAE 5W-30
Oil capacity: 1.42 L (1.5 US. qt, 1.25 Imp. qt.)
Fuel system
Type: Float type carburetor
Fuel pump Pulse type
Ignition system
Type: Electronic
Spark plug: Champion RC12YC
Champion QC12YC
Spark plug gap: 0.7-0.8 mm (0.0276-0.0315 in)
Spark plug torque: 20 N·m (2 kg·m, 14.7 ft·lb)
Armature air gap 0.25-0.36 mm (0.0098-0.0142 in)

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