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I've refurbished a vintage bike and I switched the old derailleur with a new medium cage tourney derailleur, the chain is also new and is 114 links long, which should be fine since me largest cog on the rear is 24 teeth and in the front is 52 teeth and distance between bb and cassette is 45cm, however, although I can shift to all gears the cage is really being stretched, is this a problem? should I try to refurbish the old worn derailleur?

see attached pics

Thanks in advance :)52 front, 14 back[3]: https://i.sstatic.net/eyEgP.jpg52 front, 24 back[![][2]]3

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    Looks fine to me - did you compare the number of links in the original chain vs your new one? That could be off if the new mech is a subtly different length.
    – Criggie ♦
    Commented Mar 17, 2020 at 0:10
  • In the bottom picture, is the chain on the smallest rear cog? If not, can you post a similar picture but with the chain on the smallest front chainring and the smallest rear cog? If the chain is on the smallest rear cog in the bottom picture, it sure looks like another few links in the chain wouldn't hurt...
    – Andrew Henle
    Commented Mar 17, 2020 at 9:54
  • With the large-large gear combination, is there still enough give in the rear derailleur to push the chain down to the chainstay? If yes you’ll probably be fine.
    – Michael
    Commented Mar 17, 2020 at 17:25
  • Looks ok, and simply don't ride the big/big combo anyway (google cross-chaining)
    – Lamar Latrell
    Commented Mar 18, 2020 at 8:15

2 Answers 2

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The derailleur in the second picture does not look over extended. If the derailleur has some movement left in that position then it's OK. If it's up against the limits and is being bent then you will need to lengthen the chain.

Just for future reference, you should size a chain using a proper procedure: Thread the chain around largest sprocket and chainring (not through the derailleur), find shortest chain length with where inner and outer links, add one inner and outer link.

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Since the bike will shift into the large/large combination the rear derailleur cage just needs a bit of additional range and from the picture it appears to be ok. But you need to be the judge by checking to see if the derailleur cage can be pushed up a bit. If the chain is too short the derailleur cage will be fully extended.

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