Hello Cabers! Here's a good mystery for you experts! Finishing up on of my '63 sports and am having an issue where chain is tight/loose depending on crank sprocket rotation. When you rotate the crank the chain tightens and loosens depending on the angle of the crank arm. On the drive side, when crank arm is at 9-o-clock there is 7/8" deflection but at 3-o-clock less than 1/4". With this adjustment the chain binds. Please see the pictures. I have another '63 sports that does not have this problem so in order to try to isolate the problem I did the following one at a time: 1) Swapped out chain, 2) Swapped out bottom bracket axle 3) Swapped out bottom bracket adjustable cup 4) Swapped out bottom bracket crank 5) Swapped out entire rear wheel. Also of note, I put all new bearings in bottom bracket but I did not swap out BB fixed cup. I used the friction method to remove the fixed cup on another bike but since then I heard you can damage it this way so did not on this bike. Based on everything, I think maybe the BB fixed cup is worn. The BB was definately not serviced since 1963 as it was bone dry and did not rotate freely prior to opeing it. Please see pictures of original adjustable cup as reference/clue of what fixed cup wear may look like. Lastly just FYI, I used a method found online to check for proper chainline whereby you take string and tie one end on non-drive side rear drop out loop around head tube then back to drive side rear drop out then measure distance from string on both sides as it passes seat tube ; using this admitidly crude method the frame seems very straight. From there you then measure from crank sproket to center of seat tube and use this as guide for building the rear hub( OLD (over locknut dimension) )in order to ensure the rear sprocket is in line with the crank sprocket. I did this because the hub appeared to to have been serviced at one time and based on other work on the bike I did not trust it to have been properly re-assembled. In conclusion, if I adjust the chain tightness so there is 1/2" deflection at the tightest point in the crank rotation (3-o-clock) , the loosest deflection is 1" (at 9-o-clock). For just casual riding this will probably not be an issue but I've spent so much time totally refurbishing this bike I want it to be right! Thanks for you're expertise everyone!