Restore proper CVT engagement and shift behavior on your 50cc scooter with this Universal Parts replacement torque spring for 139QMB 4-stroke engines. The torque spring sits inside the rear driven pulley (clutch side) of the CVT and controls the rate at which the belt rides up the pulley faces as engine load increases. A worn or fatigued spring causes sluggish acceleration, belt slip, and poor top-speed engagement — replacing it restores factory CVT performance.
139QMB Fitment: Designed for the 50cc 4-stroke QMB139 engine platform used across a wide range of Chinese-made scooters
97mm Overall Length: Matches OEM torque spring length for compatible driven pulleys — verify against your existing spring before ordering
57mm Width: Outer coil diameter matches the driven pulley spring seat on compatible QMB139 CVT assemblies
Conical Compression Design: Tapered coil profile provides progressive spring rate for smooth CVT engagement across the RPM range
Steel Construction: Dark oxide-coated steel wire for corrosion resistance in the CVT housing environment
Fitment
Compatible with QMB139 50cc/49cc 4-stroke CVT scooters, including:
Baja SC50
Kymco (select 50cc models)
Panterra
Roketa
Schwinn
SUNL
Tank
Various unlisted Chinese 50cc QMB139-powered scooters
Technical Specifications
Engine: QMB139 50cc / 49cc 4-stroke
Overall Length: 97mm
Width (outer diameter): 57mm
Spring Type: Conical compression (torque / driven pulley spring)
Material: Steel, dark oxide finish
MPN / SKU: 151-144
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