Yamaha MZ175

Yamaha MZ175The Yamaha MZ175 is a 171 cc (10.4 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 MZ175 engine has an OHV (overhead valve) design; float type carburetor; centrifugal flyweight governor; mechanical splashing lubrication system; Transistor Controlled Ignition (T.C.I.) and recoil or electrical (option) starter. The Yamaha MZ125 used aluminum cylinder block with the spiny cast-iron sleeve. For exhaust valve used high heat resistant SUH3 steel.

The cylinder bore is 66.0 mm (2.60 in) and the piston stroke is 50.0 mm (1.97 in), compression ratio rating is 8.5:1. The engine produced 4.8 PS (3.5 kW) at 3,600 rpm of maximum horsepower and 4.1 PS (3.0 kW) at 3,600 rpm of continuous rated power. Maximum torque is 10.5 N·m (1.07 kg·m, 7.74 ft·lb) at 2,400 rpm and 21.1 N·m (2.0 kg·m, 15.56 ft·lb) at 1,200 rpm for MZ175R model (Reduction Type).

General information

Engine Specifications
ModelMZ175
Type4-stroke, OHV, single cylinder
Displacement171 cm 3 (10.4 cu-in)
Max. horsepower4.8 PS (3.5 kW) at 3,600 rpm
Max. torque (crank PTO) MZ175: 10.5 N·m (1.07 kg·m, 7.74 ft·lb) at 2,400 rpm
MZ175R: 21.1 N·m (2.0 kg·m, 15.56 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 capacity4.5 L (1.18 US Gal)
PTO shaft rotationCounterclockwise (from PTO shaft side)

Dimensions and Weight

Yamaha MZ175
Length, mm (in)315 (12.4)
Width, mm (in)352 (13.8)
Height, mm (in)370 (14.6)
Dry weight, kg (lb)16.5 (36.4)

Cylinder Block and Head

Cylinder block
Compression ratio:8.5:1
Bore x Stroke66 X 50 mm (2.60 x 1.97 in)
Sleeve internal diameter66.005-66.015 mm (2.5986-2.5990 in)
Piston skirt outer diameter66.000 mm (2.598 in)
Number of piston rings (compression / oil):2 / 1
Ring side clearanceTop0.040-0.080 (0.0016-0.0030 in)
Second0.020-0.060 (0.0008-0.0024 in)
Ring end gapTop0.20-0.40 mm (0.008-0.016 in)
Second0.20-0.40 mm (0.008-0.016 in)
Oil0.20-0.40 mm (0.008-0.016 in)
Piston pin outer diameter15.995-16.000 mm (0.6297-0.6299 in)
Connecting rod small end inner diameter16.006-16.020 mm (0.6301-0.6307 in)
Connecting rod big end inner diameter28.000-28.015 mm (1.1023-1.1029 in)
Crankpin outer diameter28.00 mm (1.10 in)
Cylinder Head
Warpage (limit)0.10 mm (0.004 in)
Valve Arrangement:OHV
Valves:2
Valve head diameterINTAKE24.0 mm (0.94 in)
EXHAUST22.0 mm (0.87 in)
Stem outer diameter (standard):INTAKE5.5 mm (0.22 in)
EXHAUST5.5 mm (0.22 in)
Cam height:INTAKE26.9 mm (1.06 in)
EXHAUST26.68 mm (1.05 in)
Camshaft journal diameter:14.193-14.989 mm (0.5895-0.5901 in)

Tightening torque specs

Tightening torque specs
Cylinder head20 Nm; 2.0 kg·m; 14 ft·lb
Cylinder head cover10 Nm; 1.0 kg·m; 7 ft·lb
Crankcase cover22 Nm; 2.2 kg·m; 16 ft·lb
Connecting rod12 Nm; 1.2 kg·m; 9 ft·lb
Flywheel magneto65 Nm; 6.5 kg·m; 47 ft·lb
Governor arm8 Nm; 0.8 kg·m; 6 ft·lb
TCI unit10 Nm; 1.0 kg·m; 7 ft·lb
Oil drain plug17 Nm; 1.7 kg·m; 12 ft·lb

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 capacity0.6 L (0.63 US. qt, 0.53 Imp. qt.)
Carburetor
ModelMikuni BV-20-15
Bore size20/18
Main jet#81.3
Pilot jet#78.8
Float height16.0 mm (0.63 in)
Pilot screw opening2-1/8 turns out
Ignition system
Spark plugNGK: BPR4ES
Spark plug tightening torque18 Nm; 1.8 kg·m; 13 ft·lb
Spark plug gap0.7-0.8 mm (0.028-0.031 in)
Ignition coil air gap0.5 mm (0.02 in)
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