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Last year I bought a Norco Search 105 Hydro (https://www.norco.com/bikes/2018/dirt-dropbar/gravel/search-aluminum/search-a-105-hydro/) and from the beginning had bottom bracket creaking. Brought it back and they put in a 2mm spacer and creaks went away for the season. About half way through this season, they came back.

I tried to remedy myself, pulled off the cranks, pedals, bb and cleaned it all up and re-lubed and assembled. Was good for a ride or two and creaks again.

So I thought maybe it was the bb itself so went to purchase a new one but this is where I am confused...

  • Frame is 68mm
  • Original BB is a Shimano threaded mountain SM-BB52 (68mm)
  • But cranks are a road pair Shimano FC-RS510

I can't seem to find a 68mm mountain BB, everything is 68/73 which doesn't work with the road cranks because I need the spacers but then the road spindle isn't long enough. I bought a BBR60 (road BB) but the threads where resisting and I didn't want to force it so I returned it.

Any advice on how to move forward? I'm confused why they chose to a put a mountain BB with road cranks? Also should a road BB work in this setup? Did I just need to give threading it a little more muscle?

  • 68 mm is the road BB witdth. 73 mm is the mountain standard. – Paul H Sep 12 at 5:37
  • For mystery creaks when pedaling, make sure your pedal spindles aren't dry/ loose. I know they're threaded to be self-tightening, but they can still dry out and/or back off a fraction of a turn and develop a creak. Try taking the pedals off, greasing the spindle threads lightly, then putting them back on very firmly. See if the creak goes away. – SSilk Sep 12 at 14:32
  • Gave this a try already, including checking the chainrings, chain, seat rails. I'm pretty certain its either the BB or the cranks, as it gets better/worse when I touch either of those things. – slate Sep 12 at 14:39
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To use a 68/73mm bottom bracket in a 68mm bottom bracket shell, you use more spacers than the 73mm shell (normally 2 x 2.5mm spacers extra). Or in other words, you leave some spacers out when using it in a 73mm shell.

If you have a 68mm shell and road cranks, your best bet is to use a 68mm road BB. The dimensions are just a little different on the cups, as explored in this question here. The differences are slight so plenty of bikes could have a mountain HII bb with road cranks, normally without issue, but if you're wondering which to buy, I'd go with the proper road one.

Don't forget that creaks can come from lots of places, don't forget to check things like your headset, QR skewers if fitted, saddle rails etc.

If the threads were resisting, and you didn't put the wrong cup in the wrong side(!) then the threads in the frame may need 'chasing' with the proper tool. Doesn't take very long in the LBS if you don't have the tool (expensive). A clean thread typically accepts a new BB cup being threaded all the way in by hand. A rough thread however will feel tight and need some force.

I like installing a BB into a cleaned thread, threaded by hand, so that I'm confident it is not cross-threaded.

  • Thanks for the thorough explanation. I have checked headset, saddle rails, pedals, spindles etc. I'm pretty certain it's the BB or the cranks as it gets better or worse when I touch those. Also most creaks happen under force on start/stops. I'm going to bring it into the shop and see if they can remedy it, I'll mention the chasing as one side threads easily by hand, but the other has some resistance around half way in. Any idea why a manufacturer would pair a mountain BB with road cranks? Especially when the mountain BB is a 68mm version and not a 73? – slate Sep 12 at 14:46
  • The reason for the MTB BB I believe is because the rear wheel is MTB width 135 mm. That means a road BB with a road crank will give you a bad chain line. The chainrings will be too close in to the frame. You might even get interference between chainrings and chainstays. So you need to have a longer spindle than you would use with the same road cranks on a road bike. – Andrew Sep 12 at 15:18
  • @Andrew in my case the MTB BB (SM-BB52) is 68mm with no spacers on the drive side and not the more common 68-73 (which would use spacers). From what I can tell the only difference in MTB 68mm vs Road 68mm is the cup size of 11.2mm vs 10.2mm. With the road BB giving me +2mm (1mm on each side) be an issue? – slate Sep 12 at 17:36
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According to Shimano Compatibility Chart the SM-BBR60 and others (see linked chart) will work with the RS510 crank and is a threaded BB. Make sure that your BBR60 has the correct threading for your shell (English as opposed to Italian). However, looking at the Shimano specs for this, the only variable option is 68 vs. 70 mm widths, referring to bike's shell width. Keep in mind that the drive side aspect (right side adapter) is left hand threaded so must be turned anti-clockwise to tighten. Also important is meticulous thread preparation: very clean and generous grease both in the shell and on the BB adapters. Grease the spindle of the crank as well including the splines on the left side. Shimano's Dealer's Manual for your crankset and BB recommends this if creaking is noted from the BB area. Finally, adhere to the correct torque specifications for all threaded parts. See the dealers manual for these.

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