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My son has bashed up the inner ring on his crankset (Shimano FC-TY701) and since it is riveted I can't replace the bent ring. I want to replace it with something better but am not planning on upgrading the rest of the drive system (currently 3 x 8). What are my options? Will a FC-M3000, FC-MT500-3, FC-M430, or a FC-M610-L work? What specifications do I need to watch to make sure that the replacement will work? Thanks

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    How badly bashed is it? You could try straightening it out with an adjustable wrench if its not that badly off. – Batman Apr 29 '18 at 18:06
  • According to bike.shimano.com/en-EU/product/component/tourney/FC-TY701.html the crank a square taper fitment to the BB axle. So that's all you need. Ideally the tooth counts would be the same (or you could tweak things a little with a bigger big ring or whatever suits) – Criggie Apr 29 '18 at 20:11
  • This is not a high end crank (rivets are evidence of that) so a used crank from ebay or CL or whereever is a good option financially. They generally don't wear out on kids bikes. – Criggie Apr 29 '18 at 20:12
  • A friend of mine had the same problem with a crank with riveted on rings made of pressed sheet metal. He took it to shop, and they simply bent the ring back. As far as I know, it still works. – ojs Apr 29 '18 at 20:20
  • Thanks for the suggestion -- My son is 16 and hard on the bike. I tried to bend the ring back but noticed it was cracked as well. So will upgrade the crank until he saves up for a full suspension MTB – Brent Baker May 1 '18 at 7:57
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What you have is a basic 3-speed square taper crank arm built for an 8 speed chain. The important parts to consider when replacing it is the BB interface (square taper) and the chainring spacing (8 speed). If you don't want to upgrade the bottom bracket, then you will have to get another square taper crank arm.

The chainring spacing is less strict, there are differences between 8, 9, and 10 speed crank arms in the chainring spacing. You can be off by a gear or two but the shifting will be a bit less than optimal. Here's some more discussion about it. Personally I have no problem using a 10 speed crankset with an 8 speed chain/cassette on my mountain bike, but I've also been riding it long enough to be sensitive/responsive to mis-shifts that might happen because of it. I consider it an upgrade, as the 10 speed crankset is quite a bit lighter and stiffer, but if you are prioritizing reliability over eeking a bit more efficiency out of the bike, I'd stick with an 8-speed crankset.

FC-M3000 This is meant for 6/7/8 speed drivetrains and is square-taper, so it would be an exact replacement and you wouldn't have any issues or have to upgrade anything else, but it's not much of an upgrade.

FC-M430 Alivio This is a square taper 3x9 crankset, so it would work even though it is not specifically 8-speed, and looks like a solid upgrade from the most basic model.

FC-M610-L Deore This is a nice crankset. Also 2-piece BB and 10-speed spacing. I have one like it on my bike. It would work with a new BB but would be sub-optimal shifting with 8 speed. FC-MT500-3 is basically the same.

You don't need to stick with Shimano either, something like the SRAM S600 would work also, as it is 8 speed and square taper.

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  • Well answered +1 – Argenti Apparatus Apr 29 '18 at 22:21
  • Thanks Kris for the detailed response. Would an older Deore XT Crankset FC-M739 crankset designed for a 3x8 work better / be a better upgrade (assuming square taper)? – Brent Baker Apr 30 '18 at 5:26
  • Thank you! It definitely depends on the price and the condition it is in, one of the main downsides of the square taper bb is that if there is any damage to the square hole on the crank it can work it's way loose and get destroyed, so I would not buy one if there was anything less than a perfect square. Chainrings also wear out eventually, not very quickly but if it is a 10 year old crankset you would hope it was sitting in a garage somewhere for pretty much that entire time. Chainrings can be replaced, but that is often ironically more expensive than getting a new crankset. – Kris Apr 30 '18 at 7:04
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    I like your suggestion to go with the SRAM S600 square taper, and am going to try that, as it appears that this option (like the other lower end shimanos) would not require a different bottom bracket. Thanks. – Brent Baker May 1 '18 at 7:30

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