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I disassembled a Shimano FC-M442 crankset and reassembled it using its exploded view. Usually, chainrings have a special notch indicating their orientation that should align with each other as well as with the drive-side crank arm. Oddly, the exploded view for the FC-M442 suggests that the middle chainring's notch should be 90 degrees off.

FC-M442

I then compared with a similar crankset, the FC-M590, using its exploded view. All the notches on this one are aligned as expected.

FC-M590

Has someone ever seen a crankset where the chainrings' notch need not to be aligned? Could there be an error in the FC-M442 exploded view? It would not make much sense to have alignment notches if we can't rely on them when reassembling the crankset.

Edit: Unless I contact Shimano, I guess I would not know if the EV is wrong or correct. Should I reassemble the middle chainring the way the EV shows it or by aligning all the notches like pretty much every other crankset?

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  • Couldn't they have used an existing chainring design on a new crankset design?
    – Daniel R Hicks
    Commented Feb 18, 2023 at 21:31
  • @DanielRHicks that is interesting. I checked a bit more and saw the exact same part (middle chainring) used on the FC-M510 and FC-M540. Also, the FC-M442 exploded view refers to the FC-M540 for parts interchangeability but not the other way around. This may tell us that the FC-M442 was created after and may have reused an existing chainring design as you suggest. Who knows if that is the case, but it sounds plausible.
    – olliebulle
    Commented Feb 19, 2023 at 1:39

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This may be the most primitive solution, but you can try both the "erroneous" orientation in the exploded view and the orientation where the notches align towards the pedal or crank arm.

With each of the orientations, try manually derailing the chain from the larger chainring to the smaller chainring by pushing the chain towards the latter with your hand while slowly turning the crankset. Do this a couple of times and keenly observe as the chain meshes with the smaller chainring.

Whichever orientation makes the chain mesh well with the smaller chainring is likely the appropriate choice.

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  • Are not ramps and pins there to help with upshifting (from a smaller chainring to a larger one)? If so, would not it make more sense to try derailing the chain in that direction?
    – olliebulle
    Commented Mar 12, 2023 at 14:17
  • @olliebulle if Shimano's R&D is anything to be trusted with, the orientation where downshifting meshes best would also be the orientation where the upshifts are proper. If both orientations seem to have equally good downshift performance then you can check for meshing in the upshifts. In doing so, you'd need the front derailleur for proper chain upshifting.
    – Gregory Leo
    Commented Apr 13, 2023 at 2:04

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