Yamaha MX800V

Yamaha MX800VThe Yamaha MX800V is a small (824 cc, 50.3 cu-in) V-twin air-cooled four-stroke internal combustion gasoline engine with vertical shaft, manufactured by Yamaha.

The Yamaha MX800V motor has two-cylinder, overhead valves and a ball bearing supported P.T.O. The engine is equipped with an industry-standard air filtration system; float-type carburetor; T.C.I. ignition system and electric starter.

The cylinder bore and the piston stroke is 80.0 mm (3.15 in) and 82.0 mm (3.23 in), respectively. The compression ratio rating is 8.6:1. The MX800V produces 26.5 HP (19.8 kW) at 3,600 rpm of maximum gross power or 26.0 HP (19.4 kW) at 3,600 rpm of gross rated power (SAE J1995) and 62.1 Nm (6.33 kg·m, 45.8 ft·lb) at 3,100 rpm of torque.

General information

Engine Specifications
Type4-stroke, OHV, V-twin
Displacement824 cm 3 (50.3 cu-in)
Max. horsepower26.5 HP (19.8 kW) at 3,600 rpm
Max. torque (crank PTO)62.1 Nm (6.33 kg·m, 45.8 ft·lb) at 2,200 rpm
Fuel systemFloat-type carburetor
Cooling systemForced-air
Ignition systemT.C.I. ignition
Lubricating systemFull pressure with filter
Starting systemElectric starter
Stoping systemMisfire
Fuel usedUnleaded gasoline (octane number 86 or higher)
Fuel tank capacity
Fuel consumption
PTO shaft rotationCounterclockwise (from PTO shaft side)

Service Information

Maximum speed3550-3600 rpm
Cylinder compression13.4-14.8 kg/cm2 (190-210 psi)
Valve clearance
Intake valve0.07-0.13 mm (0.003-0.005 in)
Exhaust valve0.07-0.13 mm (0.003-0.005 in)
Oil system
Oil typeYamalube 4-stroke or an equivalent (SE or higher)
Recommended oilSAE 10W-30
Oil capacity2.0 L (2.11 US qt, 1.76 Imp.qt)
Ignition system
Spark plugNGK: BPR6ES
Spark plug gap0.7-0.8 mm (0.028-0.031 in)
Spark plug tightening torque20 N·m (2.0 kg·m, 14 ft·lb)

Valve clearance adjustment data

Calculate the thickness of new adjusting pad so valve clearance comes within specified values.

R = Thickness of removed adjusting pad
N = Thickness of new adjusting pad
M = Measured valve clearance

N = R + [M – 0.13 mm (0.005 in)]

Adjusting pads are available from 1.80 mm (0.0708 in) to 3.00 mm (0.1181 in), in steps of 0.05 mm (0.002 in).

R = 1.80 mm
M = 0.22 mm
N = 1.80 + (0.22 – 0.13) = 1.89 mm, round to 1.90 mm, so we need a adjusting pad with code 190.

Adjust valve celarance at 1000 hr periodic maintenance, normal operational range between periodic maintenance may be 0.02-0.2 mm (0.0008-0.01 in)

Tightening torque
Rocker arm shaft bolt4.0 Nm (0.40 kg·m, 2.9 lb·ft)
Cylinder head cover bolt11.0 N·m (1.1 kg·m, 8.0 lb·ft)
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We try to use verified sources and official documentation, however, differences between sources or errors in entering information may occur. We do not provide advice on technical issues related to the engines operation or repair. We do not recommend using provided information for engines repairing engines or spare parts ordering, use only official service manuals and spare-parts catalogs.

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