I was asked the other day how do I know a motor has been run hot? Good question, and I will show you what I look for when doing initial troubleshooting.
In every case of motor overheat, the racer is trying to extract more power from a motor by using the wrong gear for the circumstances. I harp on using temp guns, especially when changing cars or going to a new track. Always do a two minute test, pull the car and check the temp (no more than 160 degrees continuous).
This picture shows a normal winding on the stator. See the bright copper color on the wire.
The picture below is of a very overheated motor. See how dark the copper wire is, almost black as compared to the picture to the left.
On odd turn motors, you also have a collector plate is on the shaft end. In the center, top of the above picture you see a solid shiny deposit of a good solder joint.
The picture below is NOT want I want to see. Center, top you can see the fours wires from the motor winding with NO solder. This motor was so hot the solder melted at the connection and ran out the bottom of the motor. It had been toasty!
Control your temp, and you will control your motor budget.