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Naraku Crankshaft 41.4mm 16T HD Stroker (139QMB)

Naraku Crankshaft 41.4mm 16T HD Stroker (139QMB)

Description: Naraku Crankshaft 41.4mm Heavy-Duty Stroker 16-Teeth for 130QMB 49/50cc 4-stroke engine. Standard stroke 41.4mm. When used in conjunction with a 52.4mm cylinder big bore, total displacement cranks out at a whopping 89.3cc!

Naraku crankshaft in OEM-quality to match Japanese and Taiwanese alternatives. Kitted with high quality, heavy duty quality bearings which allows for longer service life and durability, far superior to low cost Chinese cranks. The quality is reflected in the price, but nothing is gained from using cheap parts, there is nothing more annoying than pushing your machine home following big end failure. Matches design and size of the original with a little extra making it a perfect choice as a standard replacement or furthermore, a perfect match up for the larger cylinder capacity kits. Supplied pre-assembled with pressed bearings. Along with the Top Racing crank, this is our favorite and when it comes to value for money, this is top choice. Oil pump drive: 16 tooth, it is very important that you check this matches your current oil pump drive as your drive may have a 22 tooth drive cog.

The crank is pre-pressed with main bearings and a rod. 139QMB engines are factory-fitted with 2 different versions of the crankshaft. The only difference is the oil pump drive cog on the right-hand side (flywheel shaft). The old version, installed in almost all scooters, has a 16-teeth oil pump drive cog on the flywheel shaft. The new version has a 22-teeth oil pump cog on the flywheel shaft.

NOTE: This Naraku Crankshaft 41.4mm has the 16-teeth oil pump drive cog on the flywheel shaft which only works in conjunction with the 33-teeth oil pump and sprocket assembly. However, you can use a machine press to remove the 16-teeth oil pump cog from the flywheel shaft of the Naraku Crankshaft 41.4mm and machine press it with the newer 22-teeth oil pump drive cog to work with the newer 47-teeth oil pump and sprocket assembly. 47-teeth oil pump sprocket assembly or 33-teeth oil pump sprocket assembly and its related timing cover are not included, sold separately.

Temperature Modification May Be Required: You'll need to heat the aluminum crankcase area where the crankshaft bearing side will be placed, in order to immediately fit the frozen Crankshaft bearing, seating flush in place. Users assume full responsibility and risk doing so using this Naraku Crankshaft.


Include the following Crankshaft stroker.

•   1x Crankshaft L: 247mm / Stroke L: 41.4mm
•   1x Piston Wrist Pin Slot ID: 13mm
•   1x Flywheel Shaft Thread: M10
•   1x Oil Pump Cog Teeth: 16
•   1x Flywheel Shaft Bearing OD: 42mm
•   1x Variator Shaft Thread: M12
•   1x Variator Shaft Splines: 26
•   1x Variator Shaft Bearing: 47mm
•   1x Made in Taiwan
   Fit Flywheel Shaft Nut: M10 / Washer: M10  Socket: 14mm
   Fit Variator Shaft Nut: M12 / Washer: M12 / Socket: 17mm
•   Fit Oil Pump Sprocket: 33T
•   Fit Timing Cover: 33T
•   Fit Oil Pump Sprocket: 33T
•   Fit Dowel Pin Set (
•   Fit Dowel Pin Set (10x20mm)
•   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 & Product Dimensions:
•    4.41 pounds | 9.724” (L) x 3.5” (W) x 3.5” (H)

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Naraku Crankshaft 41.4mm 16T HD Stroker (139QMB)
  • Stock: 39
  • Reward Points: 6
  • Part #: NK100.81
Sold: 2
Views: 7604
Price in reward points: 152