I recently bought a new Shimano BB-MT501 bottom bracket and installed it. However, once I put the Hollowtech crankset back in place, when turning the pedals there is a very obvious grinding or crunching feel. Any idea what would cause this and how to fix it, or what I did wrong?
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Did you install it using a tool to ensure proper alignment? And have you checked for any dirt between the cranks and the BB ?– BurkiCommented Mar 6 at 8:27
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Too much preload on the NDS cap? That only needs to be just finger tight.– Warren BurtonCommented Mar 6 at 8:29
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3I did clean out the dirt and it is properly aligned. I don't know what an NDS cap is. However, since posting this question I was inspecting it further and (duh!) I found that part of the grinding feeling is coming from the pedal bearings; also the chain is super stretched and not sitting on the chainring properly - so no wonder there is all this grinding! I will fix these first but that's probably it...– MattCommented Mar 6 at 9:16
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2NDS means non-drive side. I.e. the left. It’s the cap that screws into the crank spindle, somewhat analogous to your headset top cap.– Weiwen NgCommented Mar 6 at 11:20
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My mistake. In this case (hollowtech) NDS preload loads the crank onto the splines but has no influence on the BB.– Warren BurtonCommented Mar 7 at 15:41
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1 Answer
Having seen the comments, here are some general things.
If you had the BB cups in your hand and you turned the bearing's inner race, naturally you expect them to turn smoothly when new. If a bit worn, you should feel that when you turn the bearings. They will feel very slightly gritty. If very worn, they may feel very gritty.
If you turn the bearing and it feels notchy, that may mean the shell is out of round. That is, the bearings are getting squeezed at some points in the rotation. A competent shop could use sandpaper or more complex tools to get the shell within round, or you could get a warranty replacement for the frame. I'm not certain what could be done for metal frames.
On systems with preload, the bearings will feel notchy or gritty if there's too much preload. What on earth is preload? I've seen this term so often but nobody has ever explained it, you may say. This answer made an attempt to do so. But this is why the comments asked if your crank's fixing cap was tightened too much. Technically that thing is called the preload fixing bolt. You're supposed to push the spindle through, put the non-drive side arm on, then put the fixing bolt/cap in and tighten it to finger tightness, which means exert a reasonable amount of force with just two fingers on the tool, don't grab the thing and act like you're trying to squeeze all the juice out of a lemon. I realize this description is subjective but that is what they say. You would know what they mean if you try it.
For the pedals, Shimano SPD and SPD-SL pedals do actually need their preload adjusted after you service them, if you actually went and serviced them (but they can often go for a long time without servicing). Otherwise, pedals often use cartridge bearings. Sometimes those can be replaced, but you may need proprietary tooling. Usually we'd just buy new pedals. Or sometimes you can keep the spindle but buy a replacement pedal body, which contains the bearings. If you have a pedal with cup and cone bearings and it's gritty, you can try to clean the grease out and re-grease it. That may not do much. If dirt intruded into the pedal body, that would accelerate wear on the bearings, but the time to address that would have been during routine maintenance.
