Yamaha YZ125 2021 - Engine Specifications

ENGINE SPECIFICATIONS
2-2
EAM20128
ENGINE SPECIFICATIONS
Engine
Combustion cycle 2-stroke
Cooling system Liquid cooled
Induction system Reed valve
Displacement 125 cm³
Number of cylinders Single cylinder
Bore  stroke 54.0  54.5 mm (2.13  2.15 in)
Compression ratio 8.6–10.7 : 1
Starting system Kickstarter
Fuel
Recommended fuel Premium unleaded gasoline (E10 acceptable)
Fuel tank capacity 8.0 L (2.1 US gal, 1.8 Imp.gal)
Engine oil
Recommended brand YAMALUBE
Lubrication system Premix lubrication
Engine oil YAMALUBE 2R
Premix ratio 30
Transmission oil
Type Motor oil SAE 10W-40 type SG or higher
Quantity (disassembled) 0.70 L (0.74 US qt, 0.62 Imp.qt)
Quantity 0.66 L (0.70 US qt, 0.58 Imp.qt)
Cooling system
Coolant quantity
Radiator (including all routes) 0.90 L (0.95 US qt, 0.79 Imp.qt)
Radiator cap valve opening pressure 93.3–122.7 kPa (0.93–1.23 kgf/cm², 13.5–17.8
psi)
Spark plug(s)
Manufacturer/model NGK/BR9EVX
Spark plug gap 0.6–0.7 mm (0.024–0.028 in)
Cylinder head
Warpage limit 0.03 mm (0.0012 in)
Cylinder
Bore 54.000–54.014 mm (2.1260–2.1265 in)
Wear limit 54.064 mm (2.1285 in)
Piston
Piston-to-cylinder clearance 0.040–0.045 mm (0.0016–0.0018 in)
Diameter 53.957–53.972 mm (2.1243–2.1249 in)
Measuring point (from piston skirt bottom) 17.5 mm (0.69 in)
Piston pin bore inside diameter limit 15.040 mm (0.5921 in)
Piston pin outside diameter limit 14.975 mm (0.5896 in)
Piston-pin-to-piston-pin-bore clearance 0.008–0.023 mm (0.0003–0.0009 in)
Piston ring
Top ring
End gap limit 1.20 mm (0.0472 in)
Ring side clearance 0.035–0.070 mm (0.0014–0.0028 in)
Side clearance limit 0.100 mm (0.0039 in)