Originally Posted by tc3team

It sounds like the meshing of the two gears wasnt set correctly, you can usually match any pinion to spur gear providing the motor mount allows it.

You should allow a very small amount of movement between the two gears, but not so much that it stresses the two gears to stripping the teeth. you should feel probably less than 1mm of movement when you hold the pinion gear and rock the spur gear back and forth (that is a very rough estimate but its not easy to explain in words )

If the reccomendation came from a good source, I would order that spur/pinion gear, get them fitted and take things from there.

Keep an eye on the motor temperature after, say 3 minutes of use.