Motor can become warm, but should not be that uncomfortable. A lot of thing can cause excessive heat :
Bad motor height,
Too much electrical resistance,
Resistance in the gearbox (bad shimming,etc)
You'd need to ask or wait for someone more qualified to answer, but that's what I know.
K3vX | Airsoft Gunsmith/Gun doctor in training.
Feel free to contact me in your preferred language and I'll gladly answer.