The Yamaha MX400 is a 402 cc (24.5 cu-in) single-cylinder air-cooled 4-stroke internal combustion general-purpose gasoline engine with horizontal shaft manufactured by Yamaha Motor Co., Ltd.
The Yamaha MX400 engine has a hemispherical combustion chamber with V-valve layout; float type carburetor; centrifugal flyweight governor; mechanical splashing lubrication system; Transistor Controlled Ignition (T.C.I.) and recoil or electrical (option) starter. The starter knob position can be adjusted by each 45°. Microwave harden crankshaft, camshaft and balancer shaft with dual bearing support provide extremely long. The high-tech exhaust valve (Stellite® coated and tufftride® finished) resists very high temperature. To be pushed the crank down directly, the cylinder arranged off from the crankshaft center.
An 85.0 mm (3.35 in) cylinder bore and 71.0 mm (2.79 in) piston stroke give the engine a total of 402 cc of displacement. Compression ratio rating is 8.2:1. The engine produced 12.8 PS (9.4 kW) at 3,600 rpm of maximum horsepower and 10.6 PS (7.8 kW) at 3,600 rpm of continuous rated power. Maximum torque is 28.7 N·m (2.9 kg·m, 21.2 ft·lb) at 2,400 rpm of torque.
General information
| Engine Specifications | |
| Model | MX400 |
| Type | 4-stroke, Hemi-head OHV, single cylinder |
| Displacement | 402 cm3 (24.5 cu-in) |
| Max. horsepower | 12.8 PS (9.4 kW) at 3,600 rpm |
| Max. torque (crank PTO) | 28.7 N·m (2.9 kg·m, 21.2 ft·lb) at 2,400 rpm |
| Carburetor | Float type |
| Cooling system | Forced-air |
| Ignition system | Transistor Controlled Ignition (T.C.I.) |
| Lubricating system | Mechanical splashing |
| Starting system | Recoil or Electrical (option) |
| Fuel used | Unleaded gasoline (octane number 86 or higher) |
| Fuel tank capacity | 6.1 L (1.61 US Gal, 1.34 Imp Gal.) |
| PTO shaft rotation | Counterclockwise (from PTO shaft side) |
Dimensions and Weight
| Yamaha MX400 | |
| Length, mm (in) | 418 (16.5) |
| Width, mm (in) | 462 (18.2) |
| Height, mm (in) | 464 (18.3) |
| Dry weight, kg (lb) | 33.0 (72.7) |
Service Information
| Valve clearance | |
| Intake valve clearance | 0.10 mm (0.004 in) |
| Exhaust valve clearance | 0.10 mm (0.004 in) |
| Oil system | |
| Oil type | Yamalube 4-stroke or an equivalent (SE or SF) |
| Recommended oil | SAE 10W-30, 10W-40 |
| Oil capacity | 1.1 L (1.16 US. qt, 0.97 Imp. qt.) |
| Ignition system | |
| Spark plug | NGK: BPR4ES |
| Spark plug gap | 0.7-0.8 mm (0.028-0.031 in) |
| T.C.I. air gap | 0.4 ± 0.2 (0.016 ± 0.008) |
| Spark plug tightening torque | 20 N·m (2.0 kg·m, 14 ft·lb) |
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