@C&O Allan posted:Mine doesn't do this. When I've worked on my dad's brass HO engines, the hopping tends to be because the screws on the gearbox have loosened. Maybe check if that is the issue. Taking the engine apart is not too hard, at least when I did it in mine (just 4 screws to remove). The only fragile part were the wires connected to the hands rails as the antenna.
Another possible issue is if the wheels/rods are not quartered which is strain on the wheel turns that could cause the hop with the engine trying to roll the wheels.
I thought about the timing of the rods but kind of dismissed it as it is absolutely smooth in reverse. Reverse is where the front gearbox is pushing down on its nose and the driveshaft is straightest. In reverse, the nose lifts and the angle of the shaft may be too much making it bind but I'm not sure yet. The gearbox is tight (I opened it to lube it), so i think my first step will be shimming the nose to reduce the amount the nose can rise. Could simply be manufacturing tolerances in the 'floating' gearbox on the front.
