Cyma MP5: Motor works but will not attach onto the gears in the gearbox

[Shraykin]

Hello, my friend has a cyma mp5. Last year his gearbox broke so he had just ordered a CM 03 gearbox.His original gearbox was plastic and '.11' on the side of it. It said it came with a motor but did not. So we used his old motor, as we put it together, the motor just spins when it is at lowest high, when it is adjusted to the highest point, it justs hits the gear inside the gearbox and never turns. When I use my hand to hold the motor, I got it to work for a brief moment, I had to angle it onto the gear so it would connect. So I am really confused if it is the gearbox or the pinion gear/head on the motor that looks a bit smaller than other motors. Anyone know the issue? Thanks.

[HKGhost]

Did you trying shimming your gears to accept the new motor?

[Shraykin]

Nope we did not