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Bottom Bracket thread, is my frame toast?

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Bottom Bracket thread, is my frame toast?

Old 12-18-11, 11:21 AM
  #1  
wphamilton
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Bottom Bracket thread, is my frame toast?

This weekend I wanted to replace the bottom bracket in my cheap mail-order bike with a sealed Shimano BB. I use this bike for daily commuting so I don't want it out of service during the week.

Since not having a spanner I couldn't budge the non-drive side cup with a crescent or lockjaw pliers I was leery of forcing it so I rode it in to the nearby local shop that has a focus on servicing bikes. (I realize it's backwards threads)

We got it turning out but at about halfway out it seized up again and looked cross-threaded. The mechanic felt like it could ruin the thread forcing it the rest of the way and ruin the frame, and would need to keep it several days as more of a project so I just purchased some new bearings and had them put the old one back. The thought was that whoever assembled it in Taiwan or where-ever may have used a power tool and cross-threaded it it. I was happy to pay him for a bottom bracket overhaul, and frankly pleased that they're willing to work on it in the first place. But what do you think about this?

I'm mulling over buying a cartridge bb anyway, and a spanner and vice perhaps, and getting serious on the non-drive cup. Do you agree that there's a serious risk, or is it minimal? Worst case, would there may be enough thread on it - 6 to 10 turns before it seized up again - that if I force it out cross-threaded would it hold up on the replacement?

I'm planning on getting a Nashbar frame and fork some time before spring and transfer components, those that are worth transferring at least. In my situation would you just wait and forgo the cartridge BB for now or go for it and get the bb you wanted?
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Old 12-18-11, 11:28 AM
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threadless bb
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Old 12-18-11, 11:30 AM
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One comment, the non-drive side cup has conventional right handed threads on any and all types of bottom brackets. English (and the rare Swiss) bottom brackets have only the DRIVE-SIDE cup left hand (or "backwards") threaded.

Assuming your LBS can remove the old bb, they should "chase" the threads with suitable bottom bracket taps to clean up any damaged ones and that should salvage it to allow any properly threaded one to be installed.
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Old 12-18-11, 11:45 AM
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cheap mail order bike == aluminum? It could just be galling. It's really hard to cross-thread a cup, and if you do it's obviously caty-wumpus relative to the face of the bb
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Old 12-18-11, 12:32 PM
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Thanks for the advice:

Originally Posted by HillRider View Post
One comment, the non-drive side cup has conventional right handed threads on any and all types of bottom brackets. English (and the rare Swiss) bottom brackets have only the DRIVE-SIDE cup left hand (or "backwards") threaded.

Assuming your LBS can remove the old bb, they should "chase" the threads with suitable bottom bracket taps to clean up any damaged ones and that should salvage it to allow any properly threaded one to be installed.
I asked about that, but they thought it might not be feasible. I suspected an exaggeration as a way of getting out of risky servicing a cheap bike (which is understandable). Do you suppose that was the case?

They were taking it off in a left-handed thread direction, I'm sure of that. I'd got a partial turn on it in fact at the bike shop (the kid didn't have much umph), but in the right-hand direction, but then they took over and reversed it.

Which could explain things, but it sounds really weird if the bracket threads were reversed from the cup threads and it was somehow forced in anyway.

Originally Posted by unterhausen View Post
cheap mail order bike == aluminum? It could just be galling. It's really hard to cross-thread a cup, and if you do it's obviously caty-wumpus relative to the face of the bb
Yes, aluminum. It started out straight, then appeared to be caty-wumpus about half way out.

Originally Posted by reptilezs View Post
threadless bb
aha. I didn't know there was such a thing, but at first glance at $55 it looks like a feasible last resort!
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Old 12-18-11, 09:40 PM
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https://www.biketoolsetc.com/index.cg...r-Spindle&q=&s=
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Old 12-18-11, 10:14 PM
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Thanks. At those prices I think I'll order one of those and wrestle the cup off without worrying about it.
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Old 12-19-11, 08:25 AM
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Something was REALLY wrong either in the bike's initial assembly or in the frame's construction if the NDS cup came out clockwise. Either the bb's cups were installed wrong or the shell was threaded wrong.
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Old 12-19-11, 08:43 AM
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If it is indeed a LH thread on the non-driveside... I can imagine this happening even though I've never seen it. It most likely means the bottom bracket shell was oriented the wrong way at the time of the frame manufacture. Bottom brackect shells are threaded before being welded to the tubes, or the tubes being welded to the shell- if that sounds better.

If that is the case, I don't see any problem having the bottom bracket in backwards, assuming it's symetrical. Fixed cup on the non drive side? Why not? There's more strain on the left crank anyway. It could be confusing to the LBS though if they didn't know about it.
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