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 model31E777
Engine type4-stroke, OHV, single-cylinder
Displacement501 cm3, (30.6 cu·in)
Max. horsepower16.2 PS (11.9 KW; 16.0 HP) at 3,600 rpm
Max. torque
Cooling systemForced air
Air cleanerPaper filter with a foam pre-cleaner
Lubricating systemFull pressure lubrication system
Ignition systemElectronic
Fuel systemFloat type carburetor
Fuel usedGasoline
Starting systemElectric starter
GovernorMechanical 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
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 base6.0 Nm; 4.4 ft·lb
Alternator2.0 Nm; 1.5 ft·lb
Armature3.0 Nm; 2.2 ft·lb
Blower housings10.0 Nm; 7.4 ft·lb
Blower housing brackets10.0 Nm; 7.4 ft·lb
Breather3.0 Nm; 2.2 ft·lb
Carburetor to intake manifold8.0 Nm; 5.9 ft·lb
Carburetor solenoid5.0 Nm; 3.7 ft·lb
Connecting rod17.0 Nm; 12.6 ft·lb
Control bracket5.0 Nm; 3.7 ft·lb
Crankcase sump25.0 Nm; 18.5 ft·lb
Cylinder head25.0 Nm; 18.5 ft·lb
Cylinder shield5.0 Nm; 3.7 ft·lb
Exhaust manifold / adapter19.0 Nm; 14.0 ft·lb
Flywheel nut135.0 Nm; 100.0 ft·lb
Flywheel fan16.0 Nm; 11.9 ft·lb
Fuel pump10.0 Nm; 7.4 ft·lb
Governor lever nut5.0 Nm; 3.7 ft·lb
Intake manifold to cylinder head10.0 Nm; 7.4 ft·lb
Muffler10.0 Nm; 7.4 ft·lb
Oil drain plug11.0 Nm; 8.1 ft·lb
Oil fill tube10.0 Nm; 7.4 ft·lb
Oil pump cover10.0 Nm; 7.4 ft·lb
Regulator / Rectifier5.0 Nm; 3.7 ft·lb
Rewind starter3.0 Nm; 2.2 ft·lb
Rocker ball set screw or nut5.0 Nm; 3.7 ft·lb
Rocker cover7.0 Nm; 5.2 ft·lb
Starter motor16.0 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 pumpPulse type
Ignition system
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 gap0.25-0.36 mm (0.0098-0.0142 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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We try to use official documentation and verify the published data, but errors may occur. In addition, specifications of machinery and equipment may vary depending on markets and modifications. We do not recommend the use of this data for spare parts or repairs. Use official service manuals or parts catalogs for your product.

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