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Old 08-04-08, 06:29 PM   #1
awc380
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BB creaking, has plastic cup?

My crank's been creaking and clicking for a while now, and I just this afternoon took it apart, re-greased the threads of the cups on both sides and cleaned the BB shell and threads in the frame. Turns out the left (non-drive) side cup is plastic! Has anyone had this before? I didn't know you could/would make something like that out of plastic. The bike's not dept. store quality, so I am surprised unless this is just some practice I've never heard of...

The bike is a KHS Urban-X: http://www.khsbicycles.com/06_urban_x_07.htm

BUT the creak/click remains, of course. Given that I've correctly cleaned and installed the bottom bracket, and that the noise still comes from the crank: Would it either be that the crank bolts are too tight or not tight enough?

Or is it something besides the crank bolts and bottom bracket?
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Old 08-04-08, 06:33 PM   #2
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Yes, plastic is popular now, even for quality square taper bb's. Google Shimanos UN-72's and 73's - one of which is discontinued. They both, or just one, have plastic non-drive side cups that, I think, were previously metal. Some have complained that they break, even if just torqued to spec, but I doubt it will make anything more clicky. It is actually quite strong. I did experiments that involved using hammers and plastic/carbon parts that I no longer use and it took a little bit to break it. The CF parts were even stronger.....

Anyways, sounds like you did a god job on the cups so it probably isn't that. If you have the tool, yank off the cranks and grease them where the connect to the bb spindles - that might be it. There could be an off chance it could be the pedals or a few other things, but the contact point of the bb and crank is where I would think it'd be at first glance.

Good luck.

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Old 08-04-08, 07:18 PM   #3
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Yes, plastic is popular now, even for quality square taper bb's. Google Shimanos UN-72's and 73's - one of which is discontinued. They both, or just one, have plastic non-drive side cups that, I think, were previously metal. Some have complained that they break, even if just torqued to spec, but I doubt it will make anything more clicky. It is actually quite strong. I did experiments that involved using hammers and plastic/carbon parts that I no longer use and it took a little bit to break it. The CF parts were even stronger.....

Anyways, sounds like you did a god job on the cups so it probably isn't that. If you have the tool, yank off the cranks and grease them where the connect to the bb spindles - that might be it. There could be an off chance it could be the pedals or a few other things, but the contact point of the bb and crank is where I would think it'd be at first glance.

Good luck.

The plastic cups are fine at spec.

Just because the noise seems to be coming from the bb area, doesn't mean it's the bb. Please see this page:

http://www.sheldonbrown.com/creaks.html
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Old 08-04-08, 07:36 PM   #4
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Those plastic cups do not need to be incredibly tight. All they really do is make sure the BB is centered in the frame's BB tube. If you just snug them up reasonably tight you'll be fine. I cracked a couple of these before I stopped obsessing about correct torque. Even cracked, they will work just fine. Worry about torque on the drive side. That one needs to be pretty tight.
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Old 08-04-08, 08:42 PM   #5
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Yes, plastic is popular now, even for quality square taper bb's. Google Shimanos UN-72's and 73's - one of which is discontinued. They both, or just one, have plastic non-drive side cups that, I think, were previously metal. Some have complained that they break, even if just torqued to spec, but I doubt it will make anything more clicky. It is actually quite strong. I did experiments that involved using hammers and plastic/carbon parts that I no longer use and it took a little bit to break it. The CF parts were even stronger.....

Anyways, sounds like you did a god job on the cups so it probably isn't that. If you have the tool, yank off the cranks and grease them where the connect to the bb spindles - that might be it. There could be an off chance it could be the pedals or a few other things, but the contact point of the bb and crank is where I would think it'd be at first glance.

Good luck.
Good info on the plastic parts, thanks. Actually, it probably works nearly as well as metal, anyway.
Greasing the tapers! Damn! That's one thing that I DIDN'T do!

I'll do that tomorrow...
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Old 08-04-08, 08:58 PM   #6
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Greasing the tapers!
I wouldn't worry about it. You're going to open a can of worms with this.
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Old 08-05-08, 11:12 AM   #7
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If the grease didn't do it, you need Teflon tape. A lot. The plastic cup, while sometimes annoyingly easy to strip, is certainly not the problem here.
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Old 08-05-08, 12:54 PM   #8
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I wouldn't worry about it. You're going to open a can of worms with this.

Yeah, I was under the impression that you were not supposed to grease the tapers if they are alluminum (I'm assuming they are).
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Old 08-05-08, 01:35 PM   #9
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Mind if I tag along? I'm getting a nasty creaking sound, maybe from my Octalink BB. It didn't start until I had 15 miles on the bike. I was able to tighten down the crank bolts but it does not help.

Would grease on the crank to BB connection points make a difference?
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Old 08-05-08, 03:45 PM   #10
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So it's the fixed cup that's causing the creak? Or just tape up threads on both sides?

And what's the worst that could happen with grease on the tapers?
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Old 08-06-08, 12:26 AM   #11
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And what's the worst that could happen with grease on the tapers?
I wonder also. I have always done it and never had a problem. Have yet to hear not to until now.
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Old 08-06-08, 06:45 AM   #12
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The first or third time you grease the same cranks on the tapers won't make a difference. It'll be after a few mounts/dismounts and "lemme just snug up the bolt to make sure it's tight" that you'll notice something.

Then what you'll find is that the taper in the crank has stretched out and the crank is now bottomed out on the spindle's taper. This normally happens after many, many years of use (10+) but greasing the tapers can cause it to happen in a few years.

A "pressure fit" (someone with real training feel free to pipe up and call it what it's really called) relies on friction in order to hold it together. Greasing the tapers makes it too slippery, allows the bolt to push the crank further onto the taper, opens up the hole in the crank, and makes things miserable for everything except the BB.

I actually wipe down the tapers with a rag with some rubbing alcohol on it to make it as clean as possible.

I *do* grease the threads of the bolt and between the bolt head and the washer under it.

I ruined 4 or 5 various cranksets (a few Campy SR/NR, two Suntour Superbe Pro, one Gipiemme) because I greased the tapers. It took me a while to stand my ground to someone who insisted it was the right thing to do.

I also learned that if I painted the inside of a stretched taper with some spray paint, I'd buy myself a week or two of use out of my various very expensive cranks. The paint acted as a spacer to reduce the taper diameter.

Except on tapers that have stretched, or where the crank is on the wrong BB, the crank/bb taper area will usually not squeak. I've never seen one squeak.

I'd double check the fixed cup side, grease all threads including pedal and chainring bolts (but not outside the threads!), remove and clean/grease your removable dropout if you have one and reinstall. There aren't that many places where one piece meets another on a bike - you can remove, grease threads, reinstall one piece at a time. Sound travels in weird ways so it's difficult to pinpoint the source of a creak.

If you rebuild your whole bike and it's still creaking, you may have a cracked something. Bar, frame, something. My three worst creaks ended up being a cracked frame, a cracked frame, and a cracking bottom bracket spindle (which broke while I was at the front of a very large group of riders). Other bad creaks were due to "starting to fail" handlebars which I promptly replaced. One was a suspect stem - it went away when I replaced the stem but I couldn't find anything wrong with the stem I took off.

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Old 08-06-08, 04:50 PM   #13
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As stated above the plactic is normal and works just fine.

DO NOT grease a square tapered spindle! As stated also above clean the spindle and the inside of the crank arm and install them as a dry fit ( no grease). You can grease the treads of the crank bolts but do not greae the the taper end of the spindle.

As for for the noise it might sound as if it is coming from the crank/bottom bracket and this could include bad or loose pedals, loose chainring bolts, loose cassette lock ring (not the crank but can sound and feel like the crank), loose derailleur hanger bolt or even dirt between the hanger and the frame. Have you noticed if the noise goes away when you stand up and pedal? You have more load on the cranks at this point but no load on the seat and seatpost. If the noise goes away while standing up check you seatpost (yes, it is not the crank but noise travels through the frame) and see if the seatpost and frame is lubed (do not lube carbon frames or post) and also check to see if the seat is tight to the rails.

Noise will travel in the frame and I have belived it to be in the bottom bracket and it was one of the many listed above.
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Old 08-12-08, 04:52 AM   #14
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And now I am pulling cranks off and cleaning spindles for breakfast...
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Old 08-12-08, 03:43 PM   #15
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A "pressure fit" (someone with real training feel free to pipe up and call it what it's really called) relies on friction in order to hold it together. Greasing the tapers makes it too slippery, allows the bolt to push the crank further onto the taper, opens up the hole in the crank, and makes things miserable for everything except the BB.
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+2 on not lubing the spindle flats. Keep them dry and clean. It's called a 'drive fit' or 'press fit'.

Last edited by Deserted; 08-12-08 at 03:49 PM.
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