Did you test the armature with a ohm meter. Check the resistance between the three plates . All readings should be the same. Then check between the commutator plates and the armature shaft. You should not get any reading there. If it is shorted you will get a very low ohm reading as low as Zero. If these readings check out Clean out the grooves between the armature plates with a toothpick and some alcohol. You should have already done this but didn't mention it. If there is too much gunk between the plates it will short and smoke when you try to run it.
Forest
