Replacing a clockwork spring

It would help to see the underside of the locomotive... I suspect that you will need to change the termination for the outer end of the spring.  Then inside end looks like there is simply a catch on the shaft that will engage the hole in the spring, so you just connect the spring to the shaft and wind it in place.  But the outer end... I suspect it may terminate by being wrapped around a couple of slots in the frame, or around a frame member.  It appears that you have a loop end mainspring, so you may need to cut off the loop and bend the outer end of the mainspring in the hook to connect it properly.  Do you remember how it was originally connected, or can you take a couple of pictures of the underside of the mechanism?  You need to have the outer end sorted out before winding the spring in place.

Also, be very careful when cutting the wire around the new mainspring... it will expand quickly and can hurt you if you aren't careful!  I like to contain them in a heavy cardboard box, and wear leather gloves when I cut the wire.  Be sure to wear safety glasses, too.

James,

Thank you very much for your reply.  With your help, I now remember how the outer end of the spring was installed.  Snapping a few photographs before taking the old spring out would have been a good idea.  Here are some more pictures.  Thanks again!  Next I need to find an appropriate key for it.

Thanks for the pictures!  Looking at them, I am guessing that the outer end of the mainspring hooks through the two slots in the back end of the motor... is that what you remember?  If so, I would suggest the first thing you need to do is cut the loop end of the mainspring off.  You can score it and snap it (wear goggles and gloves) or take the temper out of it by heating the end cherry red with a propane torch, then cutting it off.  You will need to remove the temper to bend it into a hook eventually... but in this case, I would cut off the end, get the spring installed with a long tail hanging out of the slot, then bend the hook and finish winding it in place.  There are a couple of different ways you can install the spring.  You can connect the center, wind it into place, then feed the outer end backward through the slot.  Or, you can feed the outer end through the slot first, pull as much spring as possible through the slot, then connect the inside end and wind it into place.  Regardless, after the spring is connected to the winding shaft and fed through the slot, you will need to heat it and bend the hook shape into the outer end.  Then it can be fully wound into place and the motor should run.

Looking forward to seeing it running again!

I forgot to mention that keys can be found on EBay or from businesses that sell clock parts.  I usually get keys and mainsprings from Clockworks, but the place that sold you the spring should be able to get you a key, too.

Just a warning to anyone that may tempted to use pliers to wind up a clockwork train... those square shafts can be rounded off very easily.  I've seen quite a few shafts ruined due to using pliers or incorrect keys.  Better safe than sorry...

Yes it is.  The original spring broke about three inches in on the inside (geared shaft).  Thank you very much for your expertise!  I look forward to getting this done so I can set up the circle of track and cars.  I also noted the hook is broke that connects to the tender.  Any idea what I can replace that with?  Seems like it would be a simple find, but I haven't located one yet.  The rest of the set is absolutely beautiful with no rust or corrosion!

Second thought, I can probably make a hook by tracing the size and shape of the original.  Seems that would be a better attempt at keeping it historically accurate?

I have a different model of Bing clockwork locomotive, but it has the same basic motor... and the same hook on the back of the engine, broken off in the same place!  I think using the old hook as a pattern to make a replacement is your best option.  It should be a relatively simple project to make a suitable replacement.

That is a beautiful tender, too!

As already stated, be very careful with working with mainsprings. They can release a lot of energy very quickly. If I was doing your project I would take it to a good clock repair shop. They have special 'C' rings that hold the spring wound while replacing it. Be Careful!

Always good advice to be careful when working with mainsprings.  The "C" rings are great... but the motor has to come apart to use them, and I feel like it is a lot more trouble to disassemble the motor than to wind a mainspring into an assembled motor.

Don't know that this will help, but here is a video I made of a Marx windup motor repair:

Yes, my father has those 'C' rings he uses on his clock repairs, however as James said, you need to pull the motor apart and that is something I don't want to do.  The leather gloves will have to work.  Thank you for your advice!

You are a fast worker!  I like how you used the pipe.  Thanks!