Yamaha MX400

Yamaha MX400The 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
Type4-stroke, Hemi-head OHV, single cylinder
Displacement402 cm3 (24.5 cu-in)
Max. horsepower12.8 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
CarburetorFloat type
Cooling systemForced-air
Ignition systemTransistor Controlled Ignition (T.C.I.)
Lubricating systemMechanical splashing
Starting systemRecoil or Electrical (option)
Fuel usedUnleaded gasoline (octane number 86 or higher)
Fuel tank capacity6.1 L (1.61 US Gal, 1.34 Imp Gal.)
PTO shaft rotationCounterclockwise (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 clearance0.10 mm (0.004 in)
Exhaust valve clearance0.10 mm (0.004 in)
Oil system
Oil typeYamalube 4-stroke or an equivalent (SE or SF)
Recommended oilSAE 10W-30, 10W-40
Oil capacity1.1 L (1.16 US. qt, 0.97 Imp. qt.)
Ignition system
Spark plugNGK: BPR4ES
Spark plug gap0.7-0.8 mm (0.028-0.031 in)
T.C.I. air gap0.4 ± 0.2 (0.016 ± 0.008)
Spark plug tightening torque20 N·m (2.0 kg·m, 14 ft·lb)
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