Lexmoto LSM 125 STR125YB 54mm Cylinder & Piston Kit K154FMI
Standard-bore aftermarket top-end cylinder and piston rebuild kit for the Lexmoto LSM 125 [STR125YB] using the K154FMI 4-stroke engine family. Suitable for replacing a worn, scored, seized or low-compression cylinder and piston assembly where the original dimensions match.
Components Identified From the Product Photo Set
- 1 x 54 mm air-cooled cylinder barrel / cylinder block
- 1 x standard-size aluminium piston
- 1 x complete piston-ring set
- 1 x 15 mm steel gudgeon / wrist pin
- 2 x piston-pin circlips
- 2 x valve-stem oil seals
- 1 x cylinder-head gasket
- 1 x cylinder-base gasket
- 1 x cam-chain / tensioner-area gasket as shown
Key Specification
- Model: Lexmoto LSM 125
- Model code: STR125YB
- Engine: K154FMI
- Engine type: Air-cooled 4-stroke single cylinder
- Nominal cylinder / piston diameter: 54 mm
- Gudgeon / wrist pin diameter: 15 mm
- Replacement type: Standard bore, not a big-bore conversion
- Condition: New aftermarket replacement
Lexmoto / CMPO Component Cross-References
- CMPO piston: PST026 — 54 mm piston, 15 mm pin family; EAN 5057645142126; reference OE/OEM 121000083
- CMPO piston rings: PSTR026 — 54 mm ring set for STR125YB; EAN 5057645142096; reference OE/OEM 121000080
- CMPO gudgeon pin: GDP018 — 15 mm pin for 54 mm piston family; EAN 5057645142119; reference OE/OEM 121000082
- CMPO cylinder-base gasket: GSKB014 — specifically listed for STR125YB / 154FMI; EAN 5057645173380; reference OE/OEM 149900084
- CMPO valve-stem oil seal: VLVOS004 — 154FMI / 156FMI-5 family; EAN 5057645140856; reference OE/OEM 120807007
The supplied cylinder kit is unbranded aftermarket. CMPO part numbers and reference/OE numbers are supplied for component identification and compatibility checking only and are not being presented as the manufacturer part number of the complete supplied kit.
Related Yamaha / YBR-Pattern Family
The LSM 125 K154FMI shares a number of service components with Yamaha YBR-pattern 154FMI engines. The original source kit was listed for the 54 mm Yamaha YBR125 family, and CMPO independently lists the same 54 mm piston/ring/base-gasket family for the Lexmoto LSM 125 STR125YB. Fitment should still be confirmed from the engine and physical dimensions before installation.
Fitment
- Lexmoto LSM 125
- Model code: STR125YB
- Engine code: K154FMI
Compatibility Check Before Ordering
- Confirm the motorcycle is an LSM 125 STR125YB with the K154FMI engine
- Measure the original cylinder bore / piston diameter — this kit is the standard 54 mm family
- Confirm the original piston uses a 15 mm gudgeon pin
- Compare the cylinder height, lower sleeve/spigot diameter and cooling-fin shape with the photographs
- Compare the cylinder-stud pattern and cam-chain tunnel with the existing engine
- Compare the piston crown, skirt, ring-groove layout and pin position
- Compare the head-gasket, base-gasket and tensioner-gasket profiles before fitting
Do not order solely from the motorcycle badge if the engine has been replaced or modified. The stamped engine code and physical dimensions should take priority.
Installation Notes
Top-end engine work should be carried out using the correct workshop procedure. Clean all gasket faces and oil passages, check piston-to-cylinder clearance and piston-ring end gaps, lubricate the piston and bore before assembly, install the piston in the correct orientation, fit new circlips securely and set valve timing correctly. Tighten cylinder-head fasteners to the correct engine specification and check valve clearances before starting the engine.
What Is Included
One cylinder/piston top-end kit containing the cylinder barrel, piston, piston-ring set, 15 mm wrist pin, two retaining clips, two valve-stem seals and the gaskets shown in the product photographs. Cylinder head, valves, camshaft, cam chain, tensioner assembly and engine fasteners are not included.
Delivery & Returns
- Free UK delivery with an estimated 2–3 working-day service
- 30-day returns, subject to the item being returned in its original condition