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Briggs and Stratton 31R977 Intek Engine

General Technical Data

Briggs and Stratton 31R977 Engine Specifications

Engine Model ............ Briggs and Stratton 31R977 Intek
Engine Type ............ 4-cycle single cylinder OHV vertical shaft air-cooled gasoline engine
Number of Cylinders ............ 1
Displacement, cu.in (cc) ............ 30.5 (500)
Cylinder Bore, in (mm) ............ 3.56 (91.0)
Piston Stroke, in (mm) ............ 3.06 (78.0)
Rated Engine Power, hp (kW) ............ 17.5 (13.0)
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
Cooling System ............ Forced air
Ignition System ............ Electronic
Starting System ............ Electric starter
Electrical System Rating, Volts ............ 12
Charging System Rating, Amps ............ 9

Fuel System

Fuel System Type ............ Carburetor
Carburetor Type ............ Float
Fuel Pump ............ Integral type
Governor Type ............ Mechanical
Fuel Type ............ Gasoline

Dimensions and Weight

Overall Length, in (mm) ............ 18.3 (462)
Overall Width, in (mm) ............ 14.8 (375)
Overall Height, in (mm) ............ 12.8 (324)
Net Weight, lbs (kg) ............ 79.2 (36.0)

Briggs and Stratton 31R977 Maintenance Data

Cylinder Block and Valves

Cylinder Bore Inside Diameter (Maximum), in (mm) ............ 3.567 (90.60)
Cylinder Head (Max. Out of Flatness), in (mm) ............ 0.004 (0.10)
Valve Clearance (Intake), in (mm) ............ 0.003-0.005 (0.08-0.13)
Valve Clearance (Exhaust), in (mm) ............ 0.005-0.007 (0.13-0.18)

Engine Oil and Filters

Engine Oil Type (Summer) ............ SAE 30, 10W-30
Engine Oil Type (Winter) ............ SAE 5W-30
API Service Classifications ............ SF, SG, SH, SJ or higher
Oil Capacity, qts (L) ............ 1.51 (1.42)
Oil Filter Part Number ............ 492932S/696854
Air Filter Element Part Number ............ 594201

Ignition System

Spark Plug Type ............ Champion RC12YC
Spark Plug Gap, in (mm) ............ 0.03 (0.76)
Armature Air Gap, in (mm) ............ 0.010-0.014 (0.25-0.36)
Spark Plug Torque, Nm (lb-ft) ............ 20 (14.8)

Service Intervals

Service Air Filter Pre-Cleaner ............ Every 25 hours
Clean Air Filter ............ Every 25 hours
Change Engine Oil ............ Every 50 hours
Check and Adjust Spark Plug ............ Every 50 hours
Change Engine Oil Filter ............ Every 100 hours
Replace Air Filter ............ Every 100 hours
Replace Inline Fuel Filter ............ Every 100 hours
Check Carburetor Adjustment ............ Every 100 hours
Replace Spark Plug ............ Every 100 hours
Check Valve Clearance ............ Every 200 hours

Briggs and Stratton 31R977 Service Specifications

Cylinder Block

Cylinder Bore Inside Diameter (Standard), in (mm) ............ 3.563 (90.50)
Cylinder Bore Inside Diameter (Maximum), in (mm) ............ 3.567 (90.60)
Cylinder Bore (Out-Of-Round), in (mm) ............ 0.0015 (0.04)
Main Bearing Bore Diameter (Cylinder Block), in (mm) ............ 1.3795 (35.04)
Main Bearing Bore Diameter (Crankcase Cover), in (mm) ............ 1.063 (27.00)
Camshaft Bearing Bore Diameter (Cylinder Block), in (mm) ............ 0.5011 (15.88)
Camshaft Bearing Bore Diameter (Crankcase Cover), in (mm) ............ 0.501 (12.72)
Crank Pin Journal Outside Diameter (Standard), in (mm) ............ 1.4982 (38.05)
Crank Pin Journal Outside Diameter (Wear Limit), in (mm) ............ 1.497 (31.02)
Crankshaft Journal Outside Diameter (Magneto Side), in (mm) ............ 1.3775 (35.00)
Crankshaft Journal Outside Diameter (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 Outside Diameter (Magneto Side), in (mm) ............ 0.499 (12.67)
Camshaft Journal Outside Diameter (PTO Side), in (mm) ............ 0.499 (12.67)
Connecting Rod Big End Inside Diameter (Standard), in (mm) ............ 1.2505 (31.76)
Connecting Rod Big End Inside Diameter (Wear Limit), in (mm) ............ 1.2525 (31.81)
Connecting Rod Small End Inside Diameter (Standard), in (mm) ............ 0.8006 (20.33)
Connecting Rod Small End Inside Diameter (Wear Limit), in (mm) ............ 0.802 (20.37)
Counterweight Bearings Diameter (Standard), in (mm) ............ 2.207 (56.05)
Counterweight Bearings Diameter (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 Inside Diameter (Standard), in (mm) ............ 0.237 (6.02)
Valve Guide Inside Diameter (Wear Limit), in (mm) ............ 0.240 (6.10)
Intake Valve Stem Outside Diameter (Standard), in (mm) ............ 0.235 (5.97)
Intake Valve Stem Outside Diameter (Wear Limit), in (mm) ............ 0.233 (5.92)
Exhaust Valve Stem Outside Diameter (Standard), in (mm) ............ 0.235 (5.97)
Exhaust Valve Stem Outside Diameter (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 Outside Diameter (Standard), in (mm) ............ 0.7998 (20.31)
Piston Pin Outside Diameter (Wear Limit), in (mm) ............ 0.799 (20.29)
Piston Pin Bearing Inside Diameter (Standard), in (mm) ............ 0.8006 (20.33)
Piston Pin Bearing Inside Diameter (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)

Briggs and Stratton 31R977 Tightening Torque Specs

Air Cleaner Base, Lb-ft (Nm) ............ 4.4 (6.0)
Alternator, Lb-ft (Nm) ............ 1.5 (2.0)
Armature, Lb-ft (Nm) ............ 2.2 (3.0)
Blower Housings, Lb-ft (Nm) ............ 7.4 (10.0)
Blower Housing Brackets, Lb-ft (Nm) ............ 7.4 (10.0)
Breather, Lb-ft (Nm) ............ 2.2 (3.0)
Carburetor to Intake Manifold, Lb-ft (Nm) ............ 5.9 (8.0)
Carburetor Solenoid, Lb-ft (Nm) ............ 3.7 (5.0)
Connecting Rod, Lb-ft (Nm) ............ 12.6 (17.0)
Control Bracket, Lb-ft (Nm) ............ 2.2 (3.0)
Crankcase Sump, Lb-ft (Nm) ............ 18.5 (25.0)
Cylinder Head, Lb-ft (Nm) ............ 18.5 (25.0)
Cylinder Shield, Lb-ft (Nm) ............ 3.7 (5.0)
Exhaust Manifold/Adapter, Lb-ft (Nm) ............ 14.1 (19.0)
Flywheel Nut, Lb-ft (Nm) ............ 100.0 (135.0)
Flywheel Fan, Lb-ft (Nm) ............ 11.9 (16.0)
Fuel Pump, Lb-ft (Nm) ............ 7.4 (10.0)
Governor Lever Nut, Lb-ft (Nm) ............ 3.7 (5.0)
Intake Manifold to Cylinder Head, Lb-ft (Nm) ............ 7.4 (10.0)
Muffler, Lb-ft (Nm) ............ 7.4 (10.0)
Oil Drain Plug, Lb-ft (Nm) ............ 8.1 (11.0)
Oil Fill Tube, Lb-ft (Nm) ............ 7.4 (10.0)
Oil Pump Cover, Lb-ft (Nm) ............ 7.4 (10.0)
Regulator/Rectifier, Lb-ft (Nm) ............ 3.7 (5.0)
Rewind Starter, Lb-ft (Nm) ............ 2.2 (3.0)
Rocker Ball Set Screw or Nut, Lb-ft (Nm) ............ 3.7 (5.0)
Spark Plug, Lb-ft (Nm) ............ 14.8 (20.0)
Starter Motor, Lb-ft (Nm) ............ 11.9 (16.0)
Rocker Cover, Lb-ft (Nm) ............ 5.2 (7.0)