It is years since I made a chassis but have just made an 0-4-0. Unfortunately, with the connecting rods on it is a tad tight and although I can get the wheels to go round, they bind at one point. Is there a routine to work through in order to ease the connecting rods and get smooth running? I am worried I could file a bit here and another bit there, elongate holes or make them too big and make things worse. Pointers welcome!!