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I have a road bike that has a triple chainwheel setup (48x38x28)in which the chainwheels are not replaceable. (Made by SunTour) The middle chainwheel has broken a tooth so the whole thing needs to be replaced. What a waste...

Anyway, I want to upgrade to a Shimano M361 crankset with the same tooth size chainwheels (48x38x28) that has the nice benefit of having replaceable chainwheels.

I have a Shimano JIS sealed bottom bracket; 117.5 spline size on the bike right now.

My question is do I have to replace the bottom bracket with a different size or will the existing one be fine?

The three bike shops here in town were no help. One tells me it will work, one says it will not, and the last wasn't sure.

Thanks for your help!

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    Googling for images of M361 and JIS bottom bracket it appears that both are of the square taper type. So it should work. Some adjustment of the FD may be required. – Carel Jun 25 '16 at 19:31
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    Well you have to buy the crankset anyway, so get it and fit it. If it doesn't work then you can buy a new bottom bracket cartridge. Your other option is to try disassembling the old chainrings using a drill, or to try riding on the big ring instead of the middle. – Criggie Jun 25 '16 at 21:48
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    If you're just riding on the road, chances are the non-replacable chainring options are fine. Chainrings last a very long time, and the price of a replacement chainring vs a replacement crankset with these cheaper units is not all that much -- 5 bucks between a replacement big ring and the whole crankset. – Batman Jun 26 '16 at 15:59
  • Sheldon Brown (RIP) mentions in his site that a missing tooth on a chainring isn't an issue so long as the chainring is straight. Your chainrings are very durable. Personally, I'd let it ride, save my pennies for something nicer that would enhance your comfort. – user26705 Jun 26 '16 at 17:10
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The datasheet for the crankset says it calls for a 123 mm spindle length. This would mean that your crankset would sit about a half centimeter further out than the existing one if you use the Shimano recommended bottom bracket, which will affect the chainline.

I'd go for trying it out as is -- it will probably work. If the shifting is fine, and the chain isn't jumping or derailing when its not supposed to, you're good to go. If it is having problems after adjustments, get a new bottom bracket.

  • Thank you! Now there is no doubt on what needs to be done. The information will be saved for future reference. I'll order the crankset today. Stay tuned for results... – Loyd Brown Jun 27 '16 at 14:51
  • You'll need a crank puller and some grease to remove/install the new crankset: parktool.com/blog/repair-help/… – Batman Jun 27 '16 at 15:40
  • I have all the tools here; I do most work myself. It's the subtleties and calculations for certain things I'm still learning. – Loyd Brown Jun 27 '16 at 15:42

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