Does anyone know how to...

Google Man

Removing the Shell of a GP-7 Locomotive

To start, you do not have to remove the couplers but you will have to remove the hand rails from the cab and and the steps on the cab so you don't break them. There are two tabs in the rear of the shell and these must go inward to clear the frame. Grab the shell on both sides, just past the one horn on the short hood, then push inward and lift up, making sure the tabs are clear of the frame tabs. There is one tab in front of the nose of the shell--be careful as it can break. There are only three tabs on the GP-7 shell; two are in the rear on each side and the last is in the front nose. Usually when the rear tabs are clear of the frame the front will clear and the shell will come off, but be careful when doing this and watch out for the handrails so you do not break them.

http://www.atlasrr.com/Support/locoshell.htm#hogp7

Copied from the atlas site
Bob

Check your track, DCC system, and your installlation.
Read your directions?
Unless you have something that needs a heat sink, overheating for electrical components is not good.
I hate to ask , but how do you know it overheats?
Does another engine work on the track?
Bob

I don't have DCC. All I know is that the chips are sensitive to static electricity. They get zapped during installlation.
Transistors and voltage regulators do need heat sinks. It may be natural. The short may be somthing else.

Bob

Anytime you have an electronic board you insulate it from the frame with tape. A foam tape is recommended. Perhaps it applies to your motor. So look for a electrical short.

IF you never removed tape itis unlikely that you have to install some. How about a picture. You have a short or your motor is going bad.