The repair can be one of two ways. You can grind the flat spots on the shaft higher to avoid the conflict. See photo.
The spring will break and expand to bind the motor. The second way is to separate the spring tube and remove or cut off the spring.
The reassemble, here is the assembled measurement
Then weld, and grind smooth the tube. Be SURE to replace the steel shear pin with a brass one on the propeller.
