Yamaha MZ175

The 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
Model	MZ175
Type	4-stroke, OHV, single cylinder
Displacement	171 cm 3 (10.4 cu-in)
Max. horsepower	4.8 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
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	4.5 L (1.18 US Gal)
PTO shaft rotation	Counterclockwise (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 Stroke		66 X 50 mm (2.60 x 1.97 in)
Sleeve internal diameter		66.005-66.015 mm (2.5986-2.5990 in)
Piston skirt outer diameter		66.000 mm (2.598 in)
Number of piston rings (compression / oil):		2 / 1
Ring side clearance	Top	0.040-0.080 (0.0016-0.0030 in)
	Second	0.020-0.060 (0.0008-0.0024 in)
Ring end gap	Top	0.20-0.40 mm (0.008-0.016 in)
	Second	0.20-0.40 mm (0.008-0.016 in)
	Oil	0.20-0.40 mm (0.008-0.016 in)
Piston pin outer diameter		15.995-16.000 mm (0.6297-0.6299 in)
Connecting rod small end inner diameter		16.006-16.020 mm (0.6301-0.6307 in)
Connecting rod big end inner diameter		28.000-28.015 mm (1.1023-1.1029 in)
Crankpin outer diameter		28.00 mm (1.10 in)
Cylinder Head
Warpage (limit)		0.10 mm (0.004 in)
Valve Arrangement:		OHV
Valves:		2
Valve head diameter	INTAKE	24.0 mm (0.94 in)
	EXHAUST	22.0 mm (0.87 in)
Stem outer diameter (standard):	INTAKE	5.5 mm (0.22 in)
	EXHAUST	5.5 mm (0.22 in)
Cam height:	INTAKE	26.9 mm (1.06 in)
	EXHAUST	26.68 mm (1.05 in)
Camshaft journal diameter:		14.193-14.989 mm (0.5895-0.5901 in)

Tightening torque specs

Tightening torque specs
Cylinder head	20 Nm; 2.0 kg·m; 14 ft·lb
Cylinder head cover	10 Nm; 1.0 kg·m; 7 ft·lb
Crankcase cover	22 Nm; 2.2 kg·m; 16 ft·lb
Connecting rod	12 Nm; 1.2 kg·m; 9 ft·lb
Flywheel magneto	65 Nm; 6.5 kg·m; 47 ft·lb
Governor arm	8 Nm; 0.8 kg·m; 6 ft·lb
TCI unit	10 Nm; 1.0 kg·m; 7 ft·lb
Oil drain plug	17 Nm; 1.7 kg·m; 12 ft·lb

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	0.6 L (0.63 US. qt, 0.53 Imp. qt.)
Carburetor
Model	Mikuni BV-20-15
Bore size	20/18
Main jet	#81.3
Pilot jet	#78.8
Float height	16.0 mm (0.63 in)
Pilot screw opening	2-1/8 turns out
Ignition system
Spark plug	NGK: BPR4ES
Spark plug tightening torque	18 Nm; 1.8 kg·m; 13 ft·lb
Spark plug gap	0.7-0.8 mm (0.028-0.031 in)
Ignition coil air gap	0.5 mm (0.02 in)