Originally Posted by acid:
Add the rods back in one step at a time and see what causes the binding?
Yes, exactly. I would suggest first putting on just the side rod that goes between the two drive wheels. A common problem is that the drive wheels are not "quartered" correctly when pressed on the axle. The side rod connects the two drive wheels together: so the off-center holes in the two drive wheels into which the side rods are screwed, need to be aligned with each other: when one is at 12:00 (top dead center), the other has to be exactly the same. That's the only way the holes will remain the same distance from each other as the wheels turn. If one is off even a few degrees, there will be part of the rotation where the wheels will turn freely, and then a part where they will bind because the distance between those holes gets closer together or further apart, making the side rod lock up. And of course, this applies to both sides of the locomotive.
if you get my drift. This is surprisingly hard to describe in words, is a visual-kinetic thing.
I have sometimes found that even after getting the wheels just right on the drive shaft, there can still be a spot where the side rods bind. In that case, I have used a drill bit or small round file to slightly enlarge or elongate the holes in the ends of the side rods. This gives a little more "play" and tolerance for variation, and has solved the problem. But get the wheels on their axles right first otherwise you'll be filing away too much of the rod.
On the other hand, if you put just the side rods on and the loco still runs free, then what I've just described here isn't the problem; then you can put on the drive rod from the front wheel to the steam chest, and see what's binding there...
