Hi everyone! I recently rediscovered my old 7715 train set and accompanying 810 motor set -- the motor and gears work perfectly after well over 30 years of storage! That said, I started thinking about upgrading the internal 4.5V motor to 9V or 12V as it will allow me to build an adapter and leverage some existing electronics (i.e. Powered Up).  Has anyone found any off-the-shelf 9V or 12V motors that will fit into the chassis with little-to-no modification?  Of course I could just buy a modern 9V train motor, but I would lose the red-wheels that match the decor of the locomotive. Here is a photo of the motor from the 810 set; note that this uses a 4V Bühler DC motor, which can be directly replaced with the 12V Bühler DC motor of the same era. I found the following post detailing a modification of a similar chassis, but it looks to be from a different motor set.  It appears that there are several 4.5/9/12V motor kits that use similar chassis, but with different internals/gearing. Finally, it looks like the 9V Lego M Power Functions motor from set 8883 may be a suitable candidate, though the driving cog might not align with the gears in the 810 motor. Any help in finding a compatible DC motor would be appreciated!  Totally ready to resign to buying a new 9V Powered-Up motor and work with that too :)