If you want to use a standard 540 size motor, you’ll need to replace parts #1 (lower chassis), #2 (upper chassis), #23 right and left (fender arms) and the motor axle. Moreover, you’ll need to add pinion and gear parts that are not present on the original design.
Download Original OpenRC tractor from here ⇓
Download motor mod from here ⇓
See pictures for more detail.
Enjoy!!
Can you tell size off bearings i cant find them
You can check size at the original tractor download page, on the BOM pdf document (https://www.myminifactory.com/object/openrc-tractor-26360). There are also links to buy them, but I see that the bearings are currently sold out.
Alternatively, you can also buy them from here: http://s.click.aliexpress.com/e/Bi2Z7IQ
Thanks for your interest!