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Briggs and Stratton 31P777 Specs
The Briggs and Stratton 31P777 is a 501 cc (30.6 cubic inches) single-cylinder air-cooled 4-cycle internal combustion gasoline engine, manufactured by Briggs and Stratton.
The Briggs 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 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 output 18.6 PS (13.7 KW; 18.5 HP) at 3,600 rpm of maximum power.
Engine code identification:
31 - Total displacement,
P - Basic design series,
7 - Vertical PTO-shaft,
7 - Plain bearing, Pressure lubrication,
7 - Electric starter.
| General Technical Data |
Engine Model ................ Briggs and Stratton 31P777
Engine Type ................ 4-cycle single cylinder OHV vertical shaft air-cooled gasoline engine
Number of Cylinders ................ 1
Displacement, cu.in (cc) ................ 30.6 (501)
Cylinder Bore, in (mm) ................ 3.56 (91.0)
Piston Stroke, in (mm) ................ 3.06 (78.0)
Rated Engine Power, hp (kW) ................ 18.5 (13.7)
Rated Engine Speed, rpm ................ 3600
Idle Speed, rpm ................ 1750
Cylinder Bore Type ................ Cast iron sleeve
Lubrication System ................ Oil pump with filter
Air Cleaner ................ Dual element (paper and foam)
Cooling System ................ Forced air
Ignition System ................ Electronic
Starting System ................ Electric starter
Electrical System Rating, Volts ................ 12
Charging System Rating, Amps ................ 8
| Fuel System |
Fuel System Type ................ Carburetor
Carburetor Type ................ Float
Fuel Pump ................ Pulse type
Governor Type ................ Mechanical
Fuel Type ................ Gasoline
| Cylinder Block |
Cylinder Bore I.D. (Standard), in (mm) ................ 3.563 (90.50)
Cylinder Bore I.D. (Maximum), in (mm) ................ 3.567 (90.60)
Cylinder Bore (Out-Of-Round), in (mm) ................ 0.0015 (0.04)
Main Bearing Bore Dia. (Cylinder Block), in (mm) ................ 1.3795 (35.04)
Main Bearing Bore Dia. (Crankcase Cover), in (mm) ................ 1.063 (27.00)
Camshaft Bearing Bore Dia. (Cylinder Block), in (mm) ................ 0.5011 (15.88)
Camshaft Bearing Bore Dia. (Crankcase Cover), in (mm) ................ 0.501 (12.72)
Crank Pin Journal O.D. (Standard), in (mm) ................ 1.4982 (38.05)
Crank Pin Journal O.D. (Wear Limit), in (mm) ................ 1.497 (31.02)
Crankshaft Journal O.D. (Magneto Side), in (mm) ................ 1.3775 (35.00)
Crankshaft Journal O.D. (PTO Side), in (mm) ................ 1.3775 (35.00)
Crankshaft Eccentrics (Standard), in (mm) ................ 2.2045 (55.91)
Crankshaft Eccentrics (Wear Limit), in (mm) ................ 2.202 (55.93)
Crankshaft End Play, in (mm) ................ 0.002-0.023 (0.05-0.58)
Camshaft Journal O.D. (Magneto Side), in (mm) ................ 0.499 (12.67)
Camshaft Journal O.D. (PTO Side), in (mm) ................ 0.499 (12.67)
Connecting Rod Big End I.D. (Standard), in (mm) ................ 1.2505 (31.76)
Connecting Rod Big End I.D. (Wear Limit), in (mm) ................ 1.2525 (31.81)
Connecting Rod Small End I.D. (Standard), in (mm) ................ 0.8006 (20.33)
Connecting Rod Small End I.D. (Wear Limit), in (mm) ................ 0.802 (20.37)
Counterweight Bearings Dia. (Standard), in (mm) ................ 2.207 (56.05)
Counterweight Bearings Dia. (Wear Limit), in (mm) ................ 2.210 (56.13)
| Cylinder Head and Valves |
Cylinder Head (Max Out of Flatness), in (mm) ................ 0.004 (0.10)
Intake Valve Clearance, in (mm) ................ 0.003-0.005 (0.08-0.13)
Exhaust Valve Clearance, in (mm) ................ 0.005-0.007 (0.13-0.18)
Valve Guide I.D. (Standard), in (mm) ................ 0.237 (6.02)
Valve Guide I.D. (Wear Limit), in (mm) ................ 0.240 (6.10)
Intake Valve Stem O.D. (Standard), in (mm) ................ 0.235 (5.97)
Intake Valve Stem O.D. (Wear Limit), in (mm) ................ 0.233 (5.92)
Exhaust Valve Stem O.D. (Standard), in (mm) ................ 0.235 (5.97)
Exhaust Valve Stem O.D. (Wear Limit), in (mm) ................ 0.233 (5.92)
Cam Lobes (Intake), in (mm) ................ 1.240 (31.49)
Cam Lobes (Exhaust), in (mm) ................ 1.240 (31.49)
| Piston and Piston Rings |
Piston Pin O.D. (Standard), in (mm) ................ 0.7998 (20.31)
Piston Pin O.D. (Wear Limit), in (mm) ................ 0.799 (20.29)
Piston Pin Bearing I.D. (Standard), in (mm) ................ 0.8006 (20.33)
Piston Pin Bearing I.D. (Wear Limit), in (mm) ................ 0.802 (20.37)
Top Ring End Gap (Standard), in (mm) ................ 0.006-0.009 (0.15-0.23)
Second Ring End Gap (Standard), in (mm) ................ 0.014-0.018 (0.35-0.45)
Oil Ring End Gap (Standard), in (mm) ................ 0.006-0.010 (0.15-0.25)
Piston Ring End Gap (Wear Limit), in (mm) ................ 0.030 (0.76)
Top Ring Side Clearance (Standard), in (mm) ................ 0.002-0.005 (0.05-0.12)
Second Ring Side Clearance (Standard), in (mm) ................ 0.002-0.005 (0.05-0.12)
Oil Ring Side Clearance (Standard), in (mm) ................ 0.002-0.005 (0.05-0.12)
Piston Ring Side Clearance (Wear Limit) ................ 0.007 (0.18)
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