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Crank too tight into new bottom bracket

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Crank too tight into new bottom bracket

Old 08-21-19, 12:15 AM
  #1  
mike_on_a_bike
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Crank too tight into new bottom bracket

Hi all, I've been reading here for some time but this is my first post. I'm an amateur learning how to replace the frequently worn things on my bikes. I've replaced a few chains, cassettes, braking components, tubes/tires, and those all went pretty smoothly once I figured out which exact metal objects I needed to get my hands on. It was easier on my old bike, a lower-end hardtail MTB, because everything was in the same 8-speed Shimano MTB product line. Now I'm replacing most of the drivetrain on my new-ish (5 months old but heavily ridden) Specialized Sirrus X. It's a 1x11 flat bar hybrid, and the usual mix of road/mtb components from various brands and non-brands in a 1x11 setup has been quite a challenge for me when it comes to choosing replacements and figuring out whether to reuse that spacer that fell out when I removed that thing. I'm generally not replacing components with the same exact ones, but keeping the same specs.

Tonight I replaced the chainring and bottom bracket, so now I need to reinstall my 2-piece crank through the new BB, but the spindle won't fit. I'm using the same crank arm/spindle as before, and I'm 99% sure the specs on the new BB are correct. It was the hardest part for me to spec (my first time replacing a BB), so I got help from a mechanic at the LBS where I got the bike, and bought the compatible one that they stock. It's a Shimano SM-BBR60, an external BB with BSA threading, 68mm long, for a 24mm diameter spindle. I used a digital caliper to verify these specs on the old BB, the spindle, the frame, everything. The only difference is that the old "Samox" brand BB I'm replacing had longer threading which goes deeper into the shell, but that doesn't affect the fit.

I've watched removal/installation tutorials where they need to tap with a mallet but this is worse. I tried using a rubber mallet but escalating from gentle taps didn't help so I quit that. It's worth noting that I did need the mallet to remove the crank from the previous bottom bracket, and that wasn't so gentle either, but this time is worse, it's beyond what I want to attempt with a carbon frame. I was able to yank the crank out again and noticed the fresh grease had taken on some rusty color, so I decided to inspect the spindle more closely. It had subtle rusting near the part that interfaces with the BB, and it felt slightly raised around that stuff. I wiped off the grease from the spindle and BB inside surface, got the caliper out again, and took more precise measurements. It's hard to get super accurate inner diameters but I took repeated measurements to get around 23.93 mm for the BB, and 24.06 outside diameter for the spindle with some variation there. I carefully removed some of the rusty color with very fine sandpaper, wiped/regreased and tried again but still too tight. I then tried a gentle metal polishing product containing citric acid (probably also has tiny abrasives), buffed w/ microfiber cloth, smooth & shiny, rinsed thoroughly and applied fresh grease, but still I can't get it through. The splines make it through fine, but just after that, somewhere between the splines and the spindle's NDS bearing surface or both, it gets jammed in the BB's DS bearing surface.

The polished spindle now measures 23.98-24.00 mm. Obviously it's still wider than the BB measurements I got, but I thought maybe it could squeeze in there as it's hard to get a true BB inner diameter with my caliper. But I'm stopping there because the crank is at spec. I don't want to introduce play in another BB if I have the wrong one or I have a bad one. I read an old thread on here where someone had mentioned sanding the BB bearing surface if it's a tight fit. I want to verify that this a thing that people have to do.

Is this a normal problem? What are the tolerances for these fits? Should I sand off more spindle or attack the BB, or return it? Tap it harder? Am I crazy? Yes. I'm going into all this detail and overthinking because there could be some other issue I'm missing. I do some really stupid things when I don't overthink.
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Old 08-21-19, 01:01 AM
  #2  
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Originally Posted by mike_on_a_bike View Post
Hi all, I've been reading here for some time but this is my first post. I'm an amateur learning how to replace the frequently worn things on my bikes. I've replaced a few chains, cassettes, braking components, tubes/tires, and those all went pretty smoothly once I figured out which exact metal objects I needed to get my hands on. It was easier on my old bike, a lower-end hardtail MTB, because everything was in the same 8-speed Shimano MTB product line. Now I'm replacing most of the drivetrain on my new-ish (5 months old but heavily ridden) Specialized Sirrus X. It's a 1x11 flat bar hybrid, and the usual mix of road/mtb components from various brands and non-brands in a 1x11 setup has been quite a challenge for me when it comes to choosing replacements and figuring out whether to reuse that spacer that fell out when I removed that thing. I'm generally not replacing components with the same exact ones, but keeping the same specs.

Tonight I replaced the chainring and bottom bracket, so now I need to reinstall my 2-piece crank through the new BB, but the spindle won't fit. I'm using the same crank arm/spindle as before, and I'm 99% sure the specs on the new BB are correct. It was the hardest part for me to spec (my first time replacing a BB), so I got help from a mechanic at the LBS where I got the bike, and bought the compatible one that they stock. It's a Shimano SM-BBR60, an external BB with BSA threading, 68mm long, for a 24mm diameter spindle. I used a digital caliper to verify these specs on the old BB, the spindle, the frame, everything. The only difference is that the old "Samox" brand BB I'm replacing had longer threading which goes deeper into the shell, but that doesn't affect the fit.

I've watched removal/installation tutorials where they need to tap with a mallet but this is worse. I tried using a rubber mallet but escalating from gentle taps didn't help so I quit that. It's worth noting that I did need the mallet to remove the crank from the previous bottom bracket, and that wasn't so gentle either, but this time is worse, it's beyond what I want to attempt with a carbon frame. I was able to yank the crank out again and noticed the fresh grease had taken on some rusty color, so I decided to inspect the spindle more closely. It had subtle rusting near the part that interfaces with the BB, and it felt slightly raised around that stuff. I wiped off the grease from the spindle and BB inside surface, got the caliper out again, and took more precise measurements. It's hard to get super accurate inner diameters but I took repeated measurements to get around 23.93 mm for the BB, and 24.06 outside diameter for the spindle with some variation there. I carefully removed some of the rusty color with very fine sandpaper, wiped/regreased and tried again but still too tight. I then tried a gentle metal polishing product containing citric acid (probably also has tiny abrasives), buffed w/ microfiber cloth, smooth & shiny, rinsed thoroughly and applied fresh grease, but still I can't get it through. The splines make it through fine, but just after that, somewhere between the splines and the spindle's NDS bearing surface or both, it gets jammed in the BB's DS bearing surface.

The polished spindle now measures 23.98-24.00 mm. Obviously it's still wider than the BB measurements I got, but I thought maybe it could squeeze in there as it's hard to get a true BB inner diameter with my caliper. But I'm stopping there because the crank is at spec. I don't want to introduce play in another BB if I have the wrong one or I have a bad one. I read an old thread on here where someone had mentioned sanding the BB bearing surface if it's a tight fit. I want to verify that this a thing that people have to do.

Is this a normal problem? What are the tolerances for these fits? Should I sand off more spindle or attack the BB, or return it? Tap it harder? Am I crazy? Yes. I'm going into all this detail and overthinking because there could be some other issue I'm missing. I do some really stupid things when I don't overthink.
Sounds like a tolerance issue. The old BB probably had a loose tolerance. I suspect that a Shimano crank is pretty much exactly 24mm in diameter and the inside of the BB is slightly undersize to create an interference fit--it is after all a soft plastic in contact with the spindle. One possibility is that the faces of the BB shell are not in perfectly aligned to each other. Maybe consider having a shop face the BB? Or try another BB--maybe try something like a FSA or Raceface 24 mm external BB.
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Old 08-21-19, 09:18 AM
  #3  
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Before you get too excited, try putting the crankset in your freezer for an hour or so and then install it.
This will shrink the OD by enough to simplify insertion, considerably less force will be needed.
It worked for me with my 30mm FSA cranks. Saw this hint on a boutique BB site where it was part of the
install instructions for their crank/BB.

Of course later removal will require some use of a hammer and large dowels, but that is the way some
crank/BB are made.

Last edited by sch; 08-21-19 at 09:22 AM.
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Old 09-25-19, 11:42 PM
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I'm following up because I should've have left the thread hanging. I like seeing how things ending up being solved, or further mystified.

I did work it out in the end, but getting it on there was more violent than I was comfortable with. I brought it to my LBS with the spindle stuck halfway in the bike (couldn't get it in or out), but they were swamped and said it would take up to a week before they can even look at it. But they reassured me that I can beat the hell out of it with the mallet. I took it back home because I'd had too many bikeless weeks recently leaving it at the shop for some small thing I hadn't yet learned to do myself or gotten tools for. All good shops around here are swamped like that now. I was in the mood to rather break something than leave it at the shop again.

I had success with a regular metal hammer and a block of wood between hammer and crank. I think metal through wood transmits more high frequency shock into the spindle, which vibrates it a little to overcomes the stiction. I could get the spindle through the BB with faster, moderate taps, whereas with the rubber mallet I was hitting it much harder without result. It was like trying to hammer a nail into wood with a pillow in the way.

I cut off a piece of a dowel that fits well for removal and saved that for my tool box. I also got a mallet with harder plastic than the softer one I'd been using, hoping that works best for most situations.

I didn't try putting the crank in the freezer, was worried it might conceal how hard it will be to remove, and later find myself unable to remove it. I'd rather get stuck at room temp and decide I need a different BB/crank combo or face alignment looked at.

I didn't get the BB shell face alignment checked, but that might explain why it was a bit harder doing it on the bike than when I tried sliding the BB on/off the spindle off the bike, though it was still pretty darn tight. I should definitely get that checked if I have a hard time with it again down the road, probably when I replace the crankset at some point.

100 miles later I removed everything again (glad I had the dowel ready) to diagnose a click that occurred every pedal revolution on the right side. Removed, cleaned, re-greased and re-tightened everything but the pedals, because I hadn't changed anything with the pedals before it happened. It would make more sense for it to be a direct mount chainring thing, or a BB thing, because I changed those things! But when I finally swapped the pedal with the same kind from my old bike, the click went away... and now the offending pedal doesn't click on my old bike now! WTF!! Maybe the fresh grease helped?

Before I solved the pedal click, I rounded out one of the crank arm pinch bolts. I was using a brand new, good quality hex bit and a torque wrench, but it somehow rounded out the head of the bolt. Before that happened it had always felt sticky getting it out after turning it, so maybe that's a warning sign. So I tried extracting it and failed, making it rounder and wider. So I took it to a different bike shop than my go-to where I got it, because I thought they might be faster (usually less busy due to their location) and I was also kind of embarrassed about all my issues lately.

Got the bike back 3 weeks later.
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Old 09-26-19, 01:15 AM
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3 weeks to remove a cap screw next time buy an easy out and tackle it yourself or stop by a regular car mechanics or an engineering shop get them to do it while you wait.
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Old 09-26-19, 01:39 AM
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Originally Posted by mike_on_a_bike View Post
...
Before I solved the pedal click, I rounded out one of the crank arm pinch bolts. I was using a brand new, good quality hex bit and a torque wrench, but it somehow rounded out the head of the bolt. Before that happened it had always felt sticky getting it out after turning it, so maybe that's a warning sign. So I tried extracting it and failed, making it rounder and wider. So I took it to a different bike shop than my go-to where I got it, because I thought they might be faster (usually less busy due to their location) and I was also kind of embarrassed about all my issues lately.

Got the bike back 3 weeks later.
A quick trick is to get a set of torx bits and find one slightly larger that you can bash into the rounded allen head, biting into the remaining metal.
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Old 09-26-19, 03:34 PM
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Originally Posted by ridelikeaturtle View Post
A quick trick is to get a set of torx bits and find one slightly larger that you can bash into the rounded allen head, biting into the remaining metal.
Tried that first and it might have worked if I'd thought to tighten up the opposite pinch bolt. I had left it loose, which left more clamping pressure on the remaining one I'm trying to remove.

Originally Posted by headasunder View Post
3 weeks to remove a cap screw next time buy an easy out and tackle it yourself or stop by a regular car mechanics or an engineering shop get them to do it while you wait.
It was a pinch bolt which is a lot tighter, but I probably could've done it with my old drill. Being unequipped to do this was another layer of frustration. I have easy-out bits that I've only used a couple times on wood screws, but I was sharing a drill with roommates that was around for years until literally a week before I actually needed it. My choice was to buy a drill that I might almost never use (I currently only do mechanical stuff that is bike related, but maybe more in the future) versus getting assistance from someone who does this a lot with tighter bolts and won't mess it up more. I hadn't thought of going somewhere other than a bike shop, but I had some questions I wanted to ask them and maybe get help with the clicking issue if that was still present after securing the arm with the other pedal. In retrospect I do wish that I'd bought or borrowed a drill, and finished it myself. There's also a volunteer-staffed DIY shop in another town that I could've driven it to. My experience there varies a lot, but this would've been a good type of problem to tackle there. At the time I was drowning in a comedy of errors, exponentially growing, breaking two things for each one I fixed. Felt like I should stop touching it and let a pro handle it. In retrospect I just missed another opportunity for hands-on experience.

I do have a small battery powered drill but it was too weak. I don't know the specs on the old drill I used to use. It was a Dewalt corded drill that felt powerful enough. That leads to a question I should maybe ask in another thread:

Does anyone recommend what to look for in a drill for this purpose? The spec on this pinch bolt was 12-15 nm which is high for a 4 mm hex. With wood screws the easy-out bits were easy to use, but the wood I was working on wasn't something I needed to protect in case the drill skipped out and left marks. Didn't feel like a lot of torque though. I don't remember that drill having a clutch for selecting torque, so maybe it would've been a bad choice after all. I assume I should look for a drill with that feature, and with a certain torque range. I was look at a bunch of drills online and was bemused that none of them document the actual in-lbs/nm delivered, it's just arbitrary numbers on a selector.

Last edited by mike_on_a_bike; 09-26-19 at 05:33 PM.
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