Description
YX 125cc cylinder head.
Material – Aluminium alloy
Piston diameter suitability – 52.4mm
Valves – Inlet 27mm / Exhaust 23mm
Cylinder head length – 91mm (machined face to machined face)
Intake port diameter – 26mm
Exhaust port diameter – 22.5mm
Made to fit – YX, Lifan, may fit other engines (check dimensions), engine code would typically be 153FMI, should also have a 52.4mm piston and not a 54mm piston, should also have an alloy barrel and not a painted black steel barrel, should also have valve inspection caps with screws and not the large 17mm nut screw off type.
Not compatible with the YX125 153FMI electric start engine as the engine stud hole centres are different.
Supplied with internals such as camshaft, valves and tappets already installed.
Note: This part will require the valve clearances/tappets to be set to IN 0.10mm & EX 0.15mm upon installation.
Genuine YX replacement cylinder head for 125cc pit bike engines. Designed to suit YX and Lifan engines running a 52.4mm piston – supplied fully assembled for a quick, no-fuss rebuild.
Specifications:
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✅ Material: Aluminium alloy
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✅ Piston Compatibility: 52.4mm only
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✅ Valve Sizes: Inlet 27mm / Exhaust 23mm
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✅ Cylinder Head Length: 91mm (machined face to machined face)
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✅ Intake Port Diameter: 26mm
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✅ Exhaust Port Diameter: 22.5mm
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✅ Includes: Pre-installed camshaft, valves, and tappets
Fitment:
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✅ Compatible Engines:
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YX & Lifan 125cc engines
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Typically, engine code 153FMI
⚠ The engine must have:
- 52.4mm piston (not 54mm)
- Alloy barrel (not black-painted steel type)
- Valve inspection caps with M6 screws on each side
- ❌ Not the caps with a large 17mm nut (see final image)
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Please Note:
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🔧 Tappets must be set to: IN 0.10mm / EX 0.15mm during installation
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🏁 Run-in required – ride at no more than 2/3 throttle for at least 2 hours to bed in valves properly
Built to match factory spec – ideal for restoring proper performance on YX and Lifan 125cc engines without second-guessing the fit.
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