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Replacing Shimano 3x9 MTB bottom bracket and - best options?

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Replacing Shimano 3x9 MTB bottom bracket and - best options?

Old 09-01-21, 02:18 PM
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Kanon25
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Replacing Shimano 3x9 MTB bottom bracket and - best options?

What might be the liighest weight and best quality options that are currently available to replace this bottom bracket and the crank (Shimano SM-BB51 bottom bracket + Deore FC-M591 3x9 crankset) which was original on the bike in 2012? The bike uses 135mm QR dropouts and has hydraulic disc brakes.

3x9 replacement would be most direct but am not opposed to going to 1x10, 1x11 or 2x if it’s straightforward enough.


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Old 09-01-21, 02:34 PM
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Shimano Deore XT FC-M760 would be a step up, I think, but a new one would be rare and expensive. Here's a used one:

https://www.ebay.com/itm/15459203949...oAAOSw4dhhLmnt

Above one looks ok except for the small chainring.

Or you can a new crankset very similar to the one you have now:

https://www.ebay.com/itm/33411801466...oAAOSw5wphHTVE

(I don't know what the difference between an FC-M590 and an FC-M591 is.)
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Old 09-01-21, 02:38 PM
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Thanks / what would the most appropriate current products that I can buy new from official sources like an online retailer or bike shop rather than EBay ?
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Old 09-01-21, 02:47 PM
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Originally Posted by Kanon25
Thanks / what would the most appropriate current products that I can buy new from official sources like an online retailer or bike shop rather than EBay ?
If you're buying new retail then I think you'll have to get a Shimano Alivio (one step lower then Deore, but brand new so it might be as good). Search for "Shimano Alivio 3x9 crankset". I'd get a "Hollowtech II" version, not an "Octalink" or square taper.

3x9 is old, so there are no new high end light weight instances that I know of. It's either new mid-low end or used higher end (or real expensive new-old-stock high end).
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Old 09-01-21, 03:11 PM
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Originally Posted by tyrion
Shimano Deore XT FC-M760 would be a step up, I think, but a new one would be rare and expensive. Here's a used one:

https://www.ebay.com/itm/15459203949...oAAOSw4dhhLmnt

Above one looks ok except for the small chainring.

Or you can a new crankset very similar to the one you have now:

https://www.ebay.com/itm/33411801466...oAAOSw5wphHTVE

(I don't know what the difference between an FC-M590 and an FC-M591 is.)
I looked at this when looking at the wear on my big chainring and seeking a replacement, and IIRC, its tooth count, and finish. 44 tooth is more common for the 59X series, but I wanted 48, and black. M591 comes with a gray finish.
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Old 09-01-21, 03:46 PM
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If you change to 2x or 1x then other stuff will need to be changed. You can put any crank in there you want that has a BB with 1.37 x 24 TPI which is also sometimes referred to as BSA or English threaded. You just need to also know the width of the BB shell on the frame which should be either 68 mm or 73 mm.

Pretty much everyone makes cranks to fit a BSA threaded shell so you should be able to find something. Try to keep it appropriate to the genre of the bike, in your case a mtn bike and what ever the number of speed on the rear is. But sometimes you can get away with cranks that are for a other speeds. IE. 10 speed crank with 11 speed rear.

Is this BB worn out? You could just replace it and keep the current cranks. Or are you wanting to change something up about the cranks too?
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Old 09-01-21, 04:01 PM
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Originally Posted by Kanon25
Thanks / what would the most appropriate current products that I can buy new from official sources like an online retailer or bike shop rather than EBay ?
With the parts shortages now, your best bet is probably to take the bike to your nearest bike shop and tell them to fix it. Let them figure out what's available and will fit your bike.

FWIW, I wouldn't mess around changing gearing systems (like 2x10 or 1x11) unless you want to buy a new bike.
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Old 09-02-21, 04:30 AM
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Thanks for all the input from everybody - that's very helpful!
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Old 09-02-21, 07:53 AM
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Just another note. You have a Hollowtech II external BB. This is still Shimano's current offering, so if there are problems with the unit, you can simply put in a new one. If it's still smooth, Deore-tier cranks on up will slide right in. It looks like Altus cranks and lower are a mix of square taper, octalink (!), and Hollowtech II.

I'm not clear on what's wrong with the current crank/BB. Worn chainrings can be replaced with exact matches, and the BB is still current.
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Old 09-02-21, 08:30 AM
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If you're just replacing the BB due to not running smooth try flushing and re-lubing the bearings. Just use a thin blade to carefully pull off the bearing seals and you'll have access to the bearings. You can even do this without removing the BB but I recommend you do so you can add a little grease to the threads to prevent corrosion while you're at it.
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Old 09-02-21, 11:45 PM
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Shimano Deore Front Chainwheel FC-M591 Exploded Parts Diagram

Might be able to locate NOS with the Shimano part number...
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