You aren't going to hurt the bearings and when people talk about bending something inside the engine it's when the engine is vapor locked [fuel inside the cylinder locking it up so it won't spin] and using a starter. When using a starter you roll the engine over by hand and stop it just off the compression stroke then hit it with the starter. You just checked to make sure the engine is rolling free. As to the back fire bending something?? Never seen that happen. If there was any problems hurting engines with electric starters then here in the states our land fills would have as many RC engines in them as plastic baby diapers, almost every one uses them summer and winter.