Hey folks, I need some help. I've got a 6 Gear Falcon Index System rear derailleur on a 24-Inch 1800 Supercycle. I recently changed my tube and did it successfully, however I found my chain had a knot and so I unscrewed the derailleur and pulleys to fix it up. After fixing the chain and screwing everything back into place, I found that the derailleur wouldn't lock (as shown in pics.) can I have some assistance please?

Derailleur:
https://i436.photobucket.com/albums/q...ps8662414d.jpg

Should look like this: https://i436.photobucket.com/albums/q...ps00b9943c.jpg

Did you take the pulley cage all the way off the derailleur body? Sometimes you have to give them an extra twist before you re-fasten it.

Remove the wheel and then the derailleur, keeping the derailleur oriented as it is now. Carefully rotate the derailleur clockwise (parallel to the wheel) one full turn and then mount back on the bike.

OR

Remove the wheel and the bolt to the bottom pulley, and remove the chain from the pulley cage, leaving the derailleur mounted. Rotate the pulley assembly one turn counter-cliockwise, then run the chain in front of the top pulley and in back of the bottom one as you mount the bottom pulley back in the cage.

That will retension the spring properly. From now on be sure to only loosen the axle nuts - not the bolt that holds the derailleur onto the dropout - and you won't get the chain in a not.

+1 the pin on the cage is supposed to hold the cage in it's tensioned position, but it has unsprung (did you loosen the lower pivot when you "unscrewed the derailleur and pulleys to fix it up"; if the pin is in the way of rotating the cage, then you will need to loosen the lower pivot, just enough so the pin will clear the derailleur body when you twist it around counter clockwise then tighten it again.