The only thing that possibly generates heat is the rotor...

This happens when there is excessive load on the motor or if there is some electrical issue with it.

Excessive load can be eg a misaligned motor cover, hardened oil or dirt in motor/gears or other stuff that generates too much work resistance for the rotor.

The most common electrical issues with DCM motors are two...

• The "too much oil" syndrome causing electrical shorts inside the motor housing, meaning that the gaps between the rotor have been filled with carbon residue and causes shorts between the rotor segments.
  Too much oil dissolve the graphite brushes faster, which will leave some gooey residue in the gaps between the rotor poles. This can be scraped off with eg a pointy wooden toothpick.
  Märklin also had a moment in time where the DCM rotor gaps had a too sharp edge that shaved the brushes quite more than intended, also building graphite residue between the rotor poles - causing shorts .

• It could also be a short in a rotor coil and then the rotor should be completely changed to a new one.
  

So the first tip is to clean the motor housing inside thoroughly in case there has been some "over-oiling" historically.
The DCM motor should only be oiled at the axle ends. Very little oil on the gears in the motor housing of course, just a small drop or so.
I would also recommend to put a small drop of oil on the first motor gear axle end that is visible on the metal side of loco housing.


In my mind, the motor shield is the least likely candidate for the problems, unless misaligned... Mechanical resistance in gears, electrical rotor issues due to too much oil or a dirty/bad rotor are my best bets...


Others may of course have better tips, and all additional suggestions towards a solution are welcome.

I had some problems with my 34341 Re 4/4II 11294 which were alleviated when I adjusted the tension applied to the brushes.
The motor had been getting hot and giving off a burnt smell.
Once I adjusted the brushes and oiled the motor, it resumed normal operation.

Have you noticed any smell? Does it smell like oil or burnt carbon? Is the lok making any unusual noise when running?

The 34341 was manufactured around the end of the period where Maerklin had been experiencing some issues with hardening oil. I don't know whether this might have played a role.

Proper maintenance should resolve your issue, especially if you replace the brushes and check the tension.

Regards

Mike C

Hi Marco

Zippo lighter fluid is often recommended in this forum and works very well.

Regards
Tor