The Briggs and Stratton 31C707 Powerbuilt 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 31C707 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 31C707 engine used a dual element air filterr. 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). The compression ratio rating is 8.5:1. This engine produced 17.7 PS (13.0 KW; 17.5 HP) at 3,300 rpm of horsepower.
The breakdown of the engine code is as follows:
- 31 – Displacement
- C – Basic design series
- 7 – Vertical PTO-shaft
- 0 – Plain bearing
- 7 – Electric starter
General information
| Engine Specifications | |
| Model | B&S 31C707 Powerbuilt |
| Type | 4-stroke, OHV, single-cylinder |
| Displacement | 501 cm 3 (30.6 cu-in) |
| Max. horsepower | 17.7 PS (13.0 KW; 17.5 HP) at 3,300 rpm |
| Max. torque | – |
| Fuel system | Float type carburetor |
| Cooling system | Forced-air |
| Ignition system | Electronic |
| Lubricating system | Splash type |
| Starting system | Electric starter |
| Fuel used | Gasoline |
| Fuel tank capacity | – |
Cylinder Block and Head
| Cylinder block | ||
| Compression ratio: | 8.5:1 | |
| 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) |
Author:
Need to know rotation.
18.5 is too tight for cylinder head bolts, I twisted a bolt off in the head before I got to 18.5 ft lbs. It should be no greater than 15 ft lbs. Thanks a lot
What is the torque for the two Valve studs? I have one that loosens every few years.