Briggs and Stratton 31C707

Briggs and Stratton 31C707The 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
ModelB&S 31C707 Powerbuilt
Type4-stroke, OHV, single-cylinder
Displacement501 cm 3 (30.6 cu-in)
Max. horsepower17.7 PS (13.0 KW; 17.5 HP) at 3,300 rpm
Max. torque
Fuel systemFloat type carburetor
Cooling systemForced-air
Ignition systemElectronic
Lubricating systemSplash type
Starting systemElectric starter
Fuel usedGasoline
Fuel tank capacity

Cylinder Block and Head

Cylinder block
Compression ratio:8.5:1
Bore x Stroke90.6 mm X 77.8 mm (3.57 x 3.06 in)
Sleeve internal diameter90.500-90.600 mm (3.563-3.5669 in)
Number of piston rings (compression / oil):2 / 1
Side clearanceTop0.05-0.12 mm (0.002-0.005 in)
Second0.05-0.12 mm (0.002-0.005 in)
Oil0.05-0.12 mm (0.002-0.005 in)
Ring end gapTop0.150-0.230 mm (0.0059-0.0091 in)
Second0.350-0.450 mm (0.0138-0.0177 in)
Oil0.150-0.250 mm (0.0059-0.0098 in)
Connecting rod small end ID20.330-20.370 mm (0.8004-0.802 in)
Piston pin outer diameter20.310-20.290 mm (0.7996-0.7988 in)
Cylinder Head
Valve Arrangement:OHV (overhead)
Valve steam diameterINTAKE5.920-5.970 mm (0.233-0.235 in)
EXHAUST5.920-5.970 mm (0.233-0.235 in)

Tightening torque specs

Tightening torque specs
Air cleaner base6.0 Nm; 4.4 ft·lb
Alternator2.0 Nm; 1.5 ft·lb
Armature3.0 Nm; 2.2 ft·lb
Blower housings10.0 Nm; 7.4 ft·lb
Blower housing brackets10.0 Nm; 7.4 ft·lb
Breather3.0 Nm; 2.2 ft·lb
Carburetor to intake manifold8.0 Nm; 5.9 ft·lb
Carburetor solenoid5.0 Nm; 3.7 ft·lb
Connecting rod17.0 Nm; 12.6 ft·lb
Control bracket5.0 Nm; 3.7 ft·lb
Crankcase sump25.0 Nm; 18.5 ft·lb
Cylinder head25.0 Nm; 18.5 ft·lb
Cylinder shield5.0 Nm; 3.7 ft·lb
Exhaust manifold / adapter19.0 Nm; 14.0 ft·lb
Flywheel nut135.0 Nm; 100.0 ft·lb
Flywheel fan16.0 Nm; 11.9 ft·lb
Fuel pump10.0 Nm; 7.4 ft·lb
Governor lever nut5.0 Nm; 3.7 ft·lb
Intake manifold to cylinder head10.0 Nm; 7.4 ft·lb
Muffler10.0 Nm; 7.4 ft·lb
Oil drain plug11.0 Nm; 8.1 ft·lb
Oil fill tube10.0 Nm; 7.4 ft·lb
Oil pump cover10.0 Nm; 7.4 ft·lb
Regulator / Rectifier5.0 Nm; 3.7 ft·lb
Rewind starter3.0 Nm; 2.2 ft·lb
Rocker ball set screw or nut5.0 Nm; 3.7 ft·lb
Rocker cover7.0 Nm; 5.2 ft·lb
Starter motor16.0 Nm; 11.9 ft·lb

Service Information

Max speed3,600 rpm
Valve clearance
Intake valve clearance0.08-0.13 mm (0.003-0.005 in)
Exhaust valve clearance0.13-0.18 mm (0.005-0.007 in)
Oil system
Oil typeAPI 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 plugChampion RC12YC
Spark plug gap0.7-0.8 mm (0.0276-0.0315 in)
Author: Sergei Wers
About: Co-founder and CEO of a multi-brand auto repair shop (engine repair, chassis repair, body repair and painting) for over 15 years. I have been developing internet sites with technical specifications for more than seven years.

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  1. 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

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