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I have noticed a lot of scraping on the inside of my Trushift 44T plate. Is it just a function of distance, time and color or is it a clue that something is not working properly? The bike was bought used.

Here is my chainring (bottom) and another from my buddy's bike. Mine did more km so it is not a perfect comparison but still: enter image description here

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Some damage is to be expected caused by upshifts, that said, anecdotally speaking (i.e., based on personal experience), that amount of damage looks excessive.

Speculation

I wonder if the front derailleur was misadjusted so that it could be in the upper position, but not far enough for the chain to properly catch and upshift. If the derailleur was left in the upper position the chain could partially catch then drop back down to the lower ring. If ignored and ridden in that position over many, many miles the chain would continual catch and drop, wearing the inner side of the ring.

In terms of upshift functionality, all that really matters is whether the ramps and pins remain functional. That is hard to assess from the photo (although I see some intact pins).

chainring ramps and pins

Next Steps

The best thing to do is make sure that the front derailleur is adjusted properly. If the upshifts are still acceptable, then don't worry about the damage as it would be largely superficial in this case (i.e., the pins and ramps can still do their job). If you cannot get it to upshift reasonably well then you should look at replacing the affected ring(s).

Finally, with that much wear it is also worth taking a look at the teeth profile the teeth themselves are excessively worn, such that a new chain may skip. This would be a different problem than the inner surface wear discussed here.

See: Does this chainring need to be replaced?

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  • That's the other question I've posted... bicycles.stackexchange.com/q/30924/14552
    – PIXP
    May 29 '15 at 21:46
  • Also I've decided to switch between the two 44t chainrings in the photo above to check the difference, if any, on tomorrow's ride.
    – PIXP
    May 29 '15 at 21:47
  • Yep, that chain ring looks pretty worn. The teeth have big flats in between.
    – andy256
    May 30 '15 at 8:10
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One thing to look for in modern chainrings is that the mark for the crank arm is matched on the chainring. The pins and ramps are meant to be at a certain point on the ring relative to the crank arm. It's possible to put the chain ring on such that the chain slides a bit before hitting the pins and ramps.

The pins are designed to shift at the lowest tension in the pedaling cycle.

There should be a small bump or mark on the chainring to indicate how it should be positioned relative to the crank arm.

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