External BB threads keep stripping
thistle_
Posts: 7,218
Went out for a ride in the sunshine this morning. Pedals felt a bit wierd and when I looked down I noticed the right hand bottom bracket cup was loose. I wasn't too far from home so went back to tighten it up, except it wouldn't because the threads had stripped off the end of the cup.
This is the second time it's happened since I changed to an external BB, both times on the RH side. The first time I put it down to bad luck, but twice in 6 months? Can anyone offer any advice on what I'm doing wrong?
The frame is a Giant Trance (X5) and the bottom brackets I've been using are Shimano Deore. When I changed to external bottom bracket, I had the frame faced and the threads re cut at the LBS and they installed it for me. 2 spacers on the RH side and 1 spacer on the LH side. I've not had any problem with the LH side, which seems to have the same or less thread inside the frame.
The threads on the cup are obviously stripped at the end (where it went into the frame) however the thread inside the frame doesn't look too bad but I expect it needs attention now.
This is the second time it's happened since I changed to an external BB, both times on the RH side. The first time I put it down to bad luck, but twice in 6 months? Can anyone offer any advice on what I'm doing wrong?
The frame is a Giant Trance (X5) and the bottom brackets I've been using are Shimano Deore. When I changed to external bottom bracket, I had the frame faced and the threads re cut at the LBS and they installed it for me. 2 spacers on the RH side and 1 spacer on the LH side. I've not had any problem with the LH side, which seems to have the same or less thread inside the frame.
The threads on the cup are obviously stripped at the end (where it went into the frame) however the thread inside the frame doesn't look too bad but I expect it needs attention now.
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What size is the BB shell? 68 or 73mm?I don't do smileys.
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Parktools0 -
Are you torqueing up the cups enough?0
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Are the threads actually stripped or are they just tapered to allow a straight fit into the frame?
Spacers are the right way. Have you measured the shell? They might of done too good a job of facing...
As SS has asked, are they torqued enough?0 -
I measured the shell and it came out as 67.22mm. That's close enough to 68mm isn't it?
I've taken a couple of photos of the first one that I broke. The threads definitely look stripped apart from where the 2 spacers have been.
They may not have been torqued correctly. I've used a Superstar BB tool (approx 15cm long) and done up as tight as I can without straining.0 -
Depends how strong you are - either doing them way too tight, or your LBS has totally stuffed up the threads. I kind of suspect the former.I don't do smileys.
There is no secret ingredient - Kung Fu Panda
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thistle (MBNW) wrote:I measured the shell and it came out as 67.22mm. That's close enough to 68mm isn't it?
I've taken a couple of photos of the first one that I broke. The threads definitely look stripped apart from where the 2 spacers have been.
It looks similar to the damage that would occur if a thread was only cut with a taper tap and not finished off with a bottoming tap. This would mean the threads farthest into the hole are not cut very deeply and then damage the peaks of the thread on the cup (see http://en.wikipedia.org/wiki/Tap_and_die for images - the cup looks a lot like the taper tap).
However, the Park BB tool only has one one tap for each side of the BB, no separate taper and bottoming taps, and other tools are probably the same. When the thread is cut the first few threads of the tap do most of the work so it is possible the LBS's BB tool is worn and isn't cutting the threads correctly in the part of the BB furthest from the face. What do the threads inside the BB look like? Are they cleanly cut or do they look similar to the cups?0 -
Overtightening is a possibility, I'll certainly bear it in mind when I next fit one.cooldad wrote:Depends how strong you are - either doing them way too tight, or your LBS has totally stuffed up the threads. I kind of suspect the former.
They look similar to the cups but not as bad, in that the threads near the outside aren't as deep as those towards the middle. They didn't look 'stripped', just not as deep. Maybe the tap didn't cut them properly? Maybe the frame is made from harder aluminium than the cups so resists stripping a bit better?dv69 wrote:What do the threads inside the BB look like? Are they cleanly cut or do they look similar to the cups?0 -
there was a issue with some cups being under size.
it could also be that your BB shell is over size a little, get engineering on it and get to measured up."Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
Parktools :?:SheldonBrown0 -
Elephant in the room.....
The cup shouldn't be undoing at all if the cranks are correctly pre-loaded......Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.0 -
has it been said the cups are undoing?The Beginner wrote:Elephant in the room.....
The cup shouldn't be undoing at all if the cranks are correctly pre-loaded......"Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
Parktools :?:SheldonBrown0 -
To be loose it has to have undone, unless there is no thread at all in the first 5mm of the shell anyway!thistle (MBNW) wrote:Went out for a ride in the sunshine this morning. Pedals felt a bit wierd and when I looked down I noticed the right hand bottom bracket cup was loose. .Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.0 -
The Beginner wrote:
To be loose it has to have undone, unless there is no thread at all in the first 5mm of the shell anyway!thistle (MBNW) wrote:Went out for a ride in the sunshine this morning. Pedals felt a bit wierd and when I looked down I noticed the right hand bottom bracket cup was loose. .
The OP only said that the cup was loose, it may have only been half a turn. Plus, the threads are damaged on the cup and possibly damaged or incorrectly cut on the BB shell so the cup wouldn't hold as tightly as would usually be expected.
If the cranks are pre-loaded correctly then there should be no slack but also no sideways force on the bearings. It should be possible to unscrew the cup to the point where the bearings are axially loaded - this may be what the OP first noticed.
It could be that the frame is a bit tougher or that if the thread was not cut deeply enough in the shell then the thin tips of the thread on the cups would be forced into uncut material on the BB shell which would flatten the thread on the cup.thistle (MBNW) wrote:Maybe the tap didn't cut them properly? Maybe the frame is made from harder aluminium than the cups so resists stripping a bit better?
I think you need to get this looked at, as Nick suggested. The LBS should have noticed if there was a problem with the thread or the cup/shell size - if the LBS had done this to my bike I'd expect them to sort it. I don't think you have overtightened the cup, the splines on the cup are in good condition. To cause this much damage to the thread by overtightening I'd expect the BB tool to cut heavily into the splines on the cup.0 -
Thanks for all the replies. I'll take it to the LBS to see what they think.
Worst case is I'll have to take it to BETD to get an insert put in.0
