Briggs and Stratton 31P777

Briggs and Stratton 31P777The Briggs and Stratton 31P777 is a 501 cc (30.6 cu·in) single-cylinder air-cooled four-stroke internal combustion gasoline engine, manufactured by Briggs and Stratton.

The B&S 31P777 engine has an OHV (overhead) design and a vertical PTO shaft. This engine is equipped with float type carburetor, pulse type fuel pump and an electronic ignition system. The B&S 31P777 engine used a dual element (paper and foam) air filter. It is equipped with an electric starter (12V).

The cylinder bore is 90.6 mm (3.57 in) and the piston stroke is 77.8 mm (3.06 in). This engine produced 18.6 PS (13.7 KW; 18.5 HP) at 3,600 rpm of horsepower.

The breakdown of the engine code is as follows:

  • 31 – Displacement
  • P – Basic design series
  • 7 – Vertical PTO-shaft
  • 7 – Plain bearing, Pressure lubrication
  • 7 – Electric starter

General information

Engine Specifications
Model B&S 31P777
Type 4-stroke, OHV, single-cylinder
Displacement 501 cm 3 (30.6 cu-in)
Max. horsepower 18.6 PS (13.7 KW; 18.5 HP) at 3,600 rpm
Max. torque
Fuel system Float type carburetor
Cooling system Forced-air
Ignition system Electronic
Lubricating system Full pressure
Starting system Electric starter
Fuel used Gasoline
Fuel tank capacity

Cylinder Block and Head

Cylinder block
Bore x Stroke 90.6 mm X 77.8 mm (3.57 x 3.06 in)
Sleeve internal diameter 90.500-90.600 mm (3.563-3.5669 in)
Number of piston rings (compression / oil): 2 / 1
Side clearance Top 0.05-0.12 mm (0.002-0.005 in)
Second 0.05-0.12 mm (0.002-0.005 in)
Oil 0.05-0.12 mm (0.002-0.005 in)
Ring end gap Top 0.150-0.230 mm (0.0059-0.0091 in)
Second 0.350-0.450 mm (0.0138-0.0177 in)
Oil 0.150-0.250 mm (0.0059-0.0098 in)
Connecting rod small end ID 20.330-20.370 mm (0.8004-0.802 in)
Piston pin outer diameter 20.310-20.290 mm (0.7996-0.7988 in)
Cylinder Head
Valve Arrangement: OHV (overhead)
Valves: 2
Valve steam diameter INTAKE 5.920-5.970 mm (0.233-0.235 in)
EXHAUST 5.920-5.970 mm (0.233-0.235 in)

Tightening torque specs

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 Information

Engine
Max speed 3,600 rpm
Valve clearance
Intake valve clearance 0.08-0.13 mm (0.003-0.005 in)
Exhaust valve clearance 0.13-0.18 mm (0.005-0.007 in)
Oil system
Oil type API SF, SG, SH, SJ or higher
Recommended oil Summer: SAE 30, 10W-30
Winter: SAE 5W-30
Oil capacity (with filter) 1.42 L (1.5 US. qt, 1.25 Imp. qt.)
Ignition system
Spark plug Champion RC12YC
Spark plug gap 0.7-0.8 mm (0.0276-0.0315 in)
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