Replacement nylon gear for Giant SyncDrive & Yamaha PW series e-bike motors
Repair your broken plastic gearwheel of the Yamaha PW series motor / Giant SyncDrive motor
Replacement plastic gear for Giant SyncDrive & Yamaha PW series e-bike motors
Giant SyncDrive / Yamaha PW-X, PW-X2, PW-ST, PW-TE, PW-CE broken gearwheel
Yamaha / Giant SyncDrive mid drive motor broken nylon gear
Yamaha mid-drive motors are also used on Giant e-bikes under the name Giant Syncdrive. These motors are reliable and have a long lifespan. Only occasionally does a problem occur: a nylon gear inside the motor can fail. Repairs are costly; sometimes a completely new motor must be purchased, costing around $750. That’s why I have developed a replacement gearwheel that you can install yourself. You can buy it on Tindie:
Included is 3 gram Molykote PG-75 grease
Worldwide shipping with tracking.
Shipping to the United States is done from the United States itself (so without the Trump tax).
The gearwheels are high-quality and precisely milled from PA66 GF30 (glass fiber reinforced polyamide 66). Note this is stronger than the original Yamaha gearwheel.
The gearwheel is compatible with the following mid-drive motors:
Yamaha PW-X, PW-X2, PW-ST, PW-TE and PW-CE (NOT for the PW-SE)
Giant SyncDrive Pro
Giant SyncDrive Sport
Please check if the external dimensions of your broken gearwheel are correct:
Yamaha / Giant plastic gearwheel dimensions
Note that I cannot give any warranty, as I am not responsible for the design of the Yamaha mid drive motor. But my gearwheel usually lasts a long time and I never get complaints.
Replacement plastic gear for Giant SyncDrive & Yamaha PW series e-bike motors
3D printed gearwheels are weak
See also the article: Yamaha PW-X2 mid-drive motor tear down.
Yamaha / Giant plastic gear
Yamaha / Giant plastic gear
Yamaha / Giant plastic gear
Bergquist thermal gap filler pads
When the printed circuit board has been removed too, it is better to replace the two 1mm tick thermal gap filler pads of 46mm x 23mm and 23mm x 10mm. This is not necessary with the 3mm thick 10x10mm pads. At Tindie you can buy the thermal gap filler pads as a product option.
See more about the thermal gap filler pads here: Yamaha PW-X2 mid-drive motor tear down.
Stick the thermal pads to the motor housing
Included Molykote PG-75 grease
I include 3cc Molykote PG-75 grease in a plastic jar.
Molykote PG-75 grease for plastic/metal combinations
You can also use Bosch gear grease drive unit.
How to replace
Remove the broken gear and glue the new one in place. Use common one or two component PU polyurethane wood glue/adhesive. PU glue has been tested in practice and is very durable. Here polyurethane glue from Bison, note that the text may differ per country, as long as it is polyurethane then it is fine. Gorilla glue is also fine, is also polyurethane.
The clearance is approximately 0.1mm, this is to allow tolerances. If the gearwheel has more play, fill it with four strips of adhesive tape, 3 mm wide, evenly distributed around the circumference. Make sure the gear remains properly centered. Then glue it as described.
You can always remove my gearwheel by heating it up a little with a heatgun, which will soften the glue.
PU glue Bison
Yamaha PW-X and PW-X2 broken gear repair
Yamaha PW-X and PW-X2 broken gear repair
Yamaha PW-X and PW-X2 broken gear
Removing the broken gearwheel
How to avoid gear overload
Nylon gearwheels have an infinite lifespan when used properly: they are used successfully in hub motors where they rarely break. The problem, however, is that the Yamaha mid-drive motors have a design flaw that causes the maximum motor torque to be greater than the gear can withstand. In order to prevent a failure again, you will have to reduce extreme loads: namely driving at full throttle at low speeds, because than the motor torque is maximum.
The nylon gearwheel often breaks immediately when the crank is suddenly blocked while driving, for instance when you hit the ground with the pedal. The gear teeth break off due to the high kinetic energy of the fast rotating motor that transfers its energy to the gear.