Solder is a generic term for metal alloys that melt at a lower temperature than the metals they are joining. Solders can melt in a range of 90 to 450 degC, above that the process is called brazing.
IF the motor is soldered at this joint (it might be brazed) then the chances are that the solder used will contain silver, and its melt point will be well over lead solder (180degC) in the range 280 to 320degC. As usual,
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Although the heat you measure on the outside of the motor is much lower - that is the surface from which heat is dissipated - it is generated inside the motor. If you get 60degC on the outside, it can be double that on the inside, and higher still at the joints where wires meet connectors. The other reason it might fail is that it wasn't fully wetted when built, the temp turns it soft, and the vibration fractures the joint. To repair it will require silver solder of the correct type, a high-temp iron (or small blowtorch) and a bit of skill.
Heat generation depends on speedo set-up and driving style as well as ratio. If you run drag brake, or use the brakes, it generates a lot more heat than if you don't. Many of the big differences in motor temps at the end of races are down to this. If you're a brake-jockey, you'll need to run lower ratios and less timing than those who can run without. These types of failures are more likely if you use brakes than if you don't, due to the momentarily higher temperatures the brakes generate, it isn't always a pointer to a manufacturing fault. HTH
