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I have a bike with a Shimano FC-M560 crankset in the front which I want to replace. I naively bought a Shimano FC-TY301 crankset, thinking that there's norms and that 3-speed cranksets are more or less interchangeable.

Fast forward; the distance between the new crankset's chainrings is larger than the old ones. Since the Shimano Deore LX derailleur doesn't go as close to the seat tube, the chain will rub against the cage when on the smallest chainring.

My question is: How do I select a part that will fit my particular derailleur without relying on the exact series? (The exact components are expensive to get at this point since they're not made anymore).

The service manual here seems to refer to a quantity named stroke, is that the relevant number here?

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    Did you already adjust derailleur limit screws? – ojs Aug 23 '18 at 12:08
  • Yes sure, I screwed them out completely and even with slack on the cable the derailleur is too close to the smallest chainring and the chain rubs. – oarfish Aug 23 '18 at 12:09
  • Are the chainrings actually more widely spaced, or just slightly more inboard? If the rings are in fact more widely spaced than your original crank you will have front shifting issues even if you get the front derailleur to adjust further inboard. What's probably going in here is that Shimano Tourney uses different chainring spacing and derailleur actuation than the older M560 groupset. – Argenti Apparatus Aug 23 '18 at 13:23
  • The spacing is slightly different and maybe the whole assembly is a bit further away from the seat tube with the M560. Bike shop told me that I need a new bottom bracket because that will move the crankset further out. Still, I guess the question stands: What information is necessary to know whether mixing components in this context works or not. – oarfish Aug 23 '18 at 15:47
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    A spacer between the right cup and the frame will move the chainrings out. – Carel Aug 24 '18 at 10:09
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According to the Bikepro.com bottom bracket compatibility page, the M560 crank requires a 113mm x 68mm bottom bracket (113 mm is the spindle length), which is in agreement with your service manual (113 mm for a 47.5 chainline, or 118 for a 50 chainline).

The Shimano FC-TY301 crankset requires a BB-UN100 / BB-UN26 bottom bracket. The BB-UN100 only comes with a spindle length of 123 mm.

What this means is that you're using a bottom bracket with a spindle length of 113 mm with a crankset that was designed to be used with a bottom bracket that has a spindle of 123 mm. Since the entire crankset it basically shifted a whole centimeter towards the frame, this could be causing the problems that you are describing.

Usually you can get away with using a different bottom bracket with a slightly shorter or longer spindle, but it appears that in your case you require the correct bottom bracket to make everything work properly.

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