The Briggs and Stratton 31N707 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 31N707 engine has an OHV (overhead) design, cast iron sleeve and a vertical PTO shaft. This engine is equipped with float type carburetor and an electronic ignition system. The B&S 31N707 engine used a dual element air filter (paper filter with a foam pre-cleaner). 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
- N – Basic design series
- 7 – Vertical PTO-shaft
- 0 – Plain bearing
- 7 – Electric starter
General information
Engine Specifications | |
Model | B&S 31N707 |
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 | Oil pump with filter |
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) |
We try to use verified sources and official documentation, however, differences between sources or errors in entering information may occur. We do not provide advice on technical issues related to the engines operation or repair. We do not recommend using provided information for engines repairing engines or spare parts ordering, use only official service manuals and spare-parts catalogs.
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