The Briggs and Stratton 251707 is a 399 cc (24.3 cu·in) single-cylinder, air-cooled, four-stroke cycle, internal combustion gasoline engine, manufactured by Briggs and Stratton.
The B&S 251707 engine has an L-head (side valve) design and a vertical PTO shaft. This engine is equipped with flo-jet carburetor, an transistor module ignition system, splash type lubrication system and 12V electric starter.
The cylinder bore is 87.30 mm (3.44 in) and the piston stroke is 66.7 mm (2.63 in). The Briggs and Stratton 251707 engine produced 10.2 PS (7.5 KW; 10.0 HP) at 3,600 rpm of horsepower.
The breakdown of the engine code is as follows:
- 25 – Displacement
- 1 – Basic design series
- 7 – Vertical PTO-shaft, Flo-Jet carburetor
- 0 – Plain bearing
- 7 – Electric starter 12V, gear drive with alternator
General information
| Engine Specifications | |
| Model | B&S 251707 |
| Type | 4-stroke, L-head, single-cylinder |
| Displacement | 399 cm 3 (24.3 cu-in) |
| Max. horsepower | 10.2 PS (7.5 KW; 10.0 HP) at 3,600 rpm |
| Max. torque | – |
| Fuel system | Flo-Jet carburetor |
| Cooling system | Forced-air |
| Ignition system | Transistor module |
| Lubrication system | Splash type |
| Starting system | Electric starter (12V) |
| Fuel used | Unleaded gasoline (octane number 86 or higher) |
| Fuel tank capacity | 3.0 liters (2.96 US.qts, 2.46 Imp. qts) |
Cylinder Block and Head
| Cylinder block | ||
| Compression ratio: | – | |
| Bore x Stroke | 87.3 mm X 66.7 mm (3.44 x 2.63 in) | |
| Sleeve internal diameter | 87.290-87.310 mm (3.4366-3.4374 in) | |
| Number of piston rings (compression / oil): | 2 / 1 | |
| Ring groove clearance | 0.228 mm (0.009 in) | |
| Ring end gap (compression ring) | 0.890 mm (0.035 in) | |
| Ring end gap (oil ring) | 1.140 mm (0.045 in) | |
| Piston pin outer diameter | 20.290 mm (0.799 in) | |
| Pin bore inner diameter | 20.350 mm (0.801 in) | |
| Connecting rod small end bearing | 20.370 mm (0.802 in) | |
| Connecting rod big end bearing | 31.800 mm (1.252 in) | |
| Crankshaft main journal diameter |
PTO side: 34.950 mm (1.376 in) Magneto side: 34.950 mm (1.376 in) |
|
| Crankpin diameter | 31.670 mm (1.2469 in) | |
| Crankshaft eccentric bearing (oscillating counterbalance) | 53.850 mm (2.120 in) | |
| Counterweight bearing (oscillating counterbalance) | 54.130 mm (2.131 in) | |
| Cylinder Head | ||
| Valve Arrangement: | L-head (sidevalve) | |
| Valves: | 2 | |
| Cam gear journal diameter: | 12.650 mm (0.498 in) | |
| Cam lobe: | 30.070 mm (1.1839 in) | |
Tightening torque specs
| Tightening torque specs | |
| Cylinder Head | 19.0 Nm (1.9 kgf·m; 14 ft·lb) |
| Connecting Rod | 21.0 Nm (2.1 kgf·m; 15.5 ft·lb) |
| Flywheel Nut | 87.8 Nm (9 kgf·m; 64.8 ft·lb) |
| Crankcase Cover | 16.0 Nm (1.6 kgf·m; 11.8 ft·lb) |
| Fuel Shut-Off Valve | 8.0 Nm (0.8 kgf·m; 5.9 ft·lb) |
| Governor Lever Nut | 7.0 Nm (0.7 kgf·m; 5.2 ft·lb) |
| Spark Plug Torque | 18.0 Nm (1.8 kgf·m; 13.3 ft·lb) |
| Oil Drain Plug | 20.0 Nm (2 kgf·m; 14.8 ft·lb) |
Service Information
| Engine | |
| Max speed | 3,600 rpm |
| Valve clearance | |
| Intake valve clearance | 0.13-0.18 mm (0.005-0.007 in) |
| Exhaust valve clearance | 0.23-0.28 mm (0.009-0.011 in) |
| Oil system | |
| Oil type | API SF, SG, SH, SJ or higher |
| Recommended oil |
Summer: SAE 30, 10W-30 Winter: SAE 5W-20, 5W-30 |
| Oil capacity (with filter) | 1.4 liters (1.5 US.qts, 1.24 Imp. qts) |
| Ignition system | |
| Spark plug | Champion CJ-8 |
| Spark plug gap | 0.762 mm (0.030 in) |
| Ignition armature air gap | 0.254-0.356 mm (0.010-0.014 in) |
Applications
The B&S 251707 engine is used on the following lawn tractors
| Model | Years Produced |
| Sears ST/10 502.25910 | 1976 |
| Simplicity Broadmoor 5010 | 1974-1976 |
| White T-100 | 1974-1976 |
| J.I. Case 110 | 1981-1985 |
| Wheel Horse A-100 | 1976–1977 |
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