I'd like to revive this thread ...
After all of my prior fiddling and restoration work, I found myself staring at my very first "coupler-ectomy" last night. Lionel postwar cast knuckle coupler from my 221T tender. The kind with the little coil spring. Except the spring on mine was broken, so the coupler wouldn't swing open by itself.
I didn't really know what the spring looked like, or how it fit. So, I bashed apart the coupler on a (separate) junker truck and "discovered" the little coil spring with its two "tails". Tiny little thing. And a bit tricky to position for the reinstall ... but I used a toothpick to line up the hole in the coupler with the coil spring "hole". Fortunately, I had some new (repro) coupler pins on hand. I used a pointy awl to improvise a "peen" on the bottom end to hold it in place.
I didn't have my camera on hand while I was working. That said, I'm curious if anyone here has discussed this topic in the past (other than G'john, above), and/or whether we might have some zoomed-in photos that show the process/assembly in some detail?
On a related note, after I got the cast coupler reassembled, I realized that I have some extra "modern" plastic knuckles that have the "whip" spring molded into them. I'm wondering (out of curiosity) if these modern plastic knuckles would fit and work in a more traditional postwar cast coupler ???
Cheers,
TJ
EDIT --
This link from JWTrains has some nice descriptions and detailed pics (albeit for an automated electromag-coil coupler). You can see the "knuckle spring" and how it fits...
http://jwtrains.com/Tech Tip_2.htm