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Polini Cylinder 50mm 81cc Nikasil Bore Kit w/Cast Piston Plus Weights (139QMB)

Polini Cylinder 50mm 81cc Nikasil Bore Kit w/Cast Piston Plus Weights (139QMB)

Description: Polini Cylinder 50mm 81cc Nikasil Bore Kit with Cast Piston Plus includes CVT roller weights for 139QMB 49/50cc 4-stroke engines. This increase in bigger bore displacement leads to an increase in performance and acceleration. The use of aluminum for this cylinder with coated chrome/nikasil plating offers superior durability and ensures very good cooling properties.

It’s also recommended to get a 50mm big valve head (Part# 1100-1239) in order to take full advantage of the bigger piston valve notch. However, you can use the original stock cylinder head without any problem.

When used in conjunction with a stock stroke of 41.4mm the engine displacement comes out to 81.3cc! When used with a 44mm stroker crank, engine displacement = 86.4cc!

NOTE: Please, measure with a caliper 139QMB crankcase bore (opening) for 54.5mm cylinder outer diameter sleeve need a minimum 54.6mm bore clearance or boring and machining are required. If, engine case must be bored, order an engine bore tool (Part# 1400-1001). 


Includes the following Cylinder, Piston + Rings, Gaskets (compression base gaskets, steel head gasket), Wrist pin, Circlips, Roller weights, and Variator slides.

•    1x Cast-Alumin Piston: 50mm
•    5x Piston Rings: 50mm
•    1x Wrist Pin w/C-clips: 38x13x9mm 
•    1x Cast-Iron Nikasil Cylinder: 50mm
•    Outer Sleeve Diameter 54.5mm
•    Cylinder Height (w/o sleeve): 53mm
•    Overall Height (w/sleeve): 70.3mm
•    6x Roller Weights: 16x13mm 5gm<9gm
•    3x Plastic Variator Slides
•    Made in Italy
•    Fit Intake Studs: M6 / Nuts: M6 Socket: 10mm
•    Fit Exhaust Studs: M6 / Nuts: M6 Socket: 10mm
•    Fit Rocker Arm Assembly: 64mm or 69mm / Feeler Gauge: .004in / .005in / Socket: 9mm
•    Fit Cylinder Studs: 168mm 176mm / Nuts: M7 / Washers: M7 / Side Bolts: M6 / Socket: 8mm-10mm
•    Fit 50mm Stud Spacing /Diagonal 70.5mm
•    Fit Cylinder Head 50mm 2V
•    Fit Crankshaft 41.4mm to 44mm
•    Fit Dowel Pin Set (
•    Fit QMB 49/50cc+

Supported Models: 139QMB 49cc-50cc engines, Baja SC50, Boreem (BMS) 50, Filly 50, Kymco 50, Panterra 50, Qingqi 50, QLink 50, Roketa 50, SUNL 50, SYM 50, Tank 50, TaoTao 50, and virtually any other scooter engine with these measurements.

Item Weight & Package Dimensions:
•    2.869 pounds | 5.7
” (L) x 5.7” (W) x 4.669” (H)

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Polini Cylinder 50mm 81cc Nikasil Bore Kit w/Cast Piston Plus Weights (139QMB)
  • Stock: 40
  • Reward Points: 13
  • Part #: 125.0007
Sold: 1
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Price in reward points: 335