ovalized bb shell or bad bb?
 

So I have a Bare knuckle track frame that I've currently been using a Miche bottom bracket on. I have had issues where the cups will tend to come loose over time and just need to be tightened which is usually no problem as it's a rare occurrence.

Today it happened again and now I'm wondering if my bb shell has become stretched/warped.

My question is for those of you with the Miche adjustable bb is there play in the cups up until you fully engage the last thread? Or are the cups tight in the shell from the first thread on?

Thanks for any help on this.

The threads are cylindrical, not tapered, so the cup should feel just about as tight on the first thread as the last. I suspect, that the threads are worn (partly stripped) from riding with a loose cup. I doubt the shell itself stretched since there's just too much meat there.

Without seeing it, I can't advise whether any repair is needed, and if so what approach to take. But it should be repairable at a fairly low cost by a decent mechanic. (finding one is the hardest part). If you'd filled in your profile showing the city, I might have been able to refer you to a decent shop.

What torque did you use when installing them?

This is non-relevant. It might account for why they loosened, but not for this thread wear pattern. In any case if it's a classic cup/cone BB he wouldn't torque the cup, just the lockring after adjusting.

I live in Boston so there are quite a few shops around here and a couple relatively within a mile or so from my house. It's not really a cone and cup but more of an adjustable cartridge Bb.

This is what it is: http://businesscycles.com/graphics/tbb-miche2.jpg

So you don't think it's ovalized? What is the repair method for this? My thoughts were since it's loose that means material is lost so re-chasing or re-tapping the threads wouldn't help. What are your thoughts?

That's not an adjustable BB, it's a straightforward cartridge held on by a pair of lockrings, which need to be set seriously tight, or with some thread locker.

Anyway, your shell isn't ovalized, but some of the thread is worn away, or mashed. On low end bikes I'd cure this down and dirty by using my 4# stonecutter's mallet to ovalize the BB, with the short radius at 6 and 12. That would bring fresh metal to a tap-able diameter, so I'd fill in the sides with some body filler, and retap the shell. The cups will get good support form the roughly 100 degrees top and bottom of meal to metal contact and the job can last for eons.

Fir a better bike, I'd ovalize less (only enough to ensure steel at the minor diameter), Retap, following the old thread, then fill the long radius area with braze or silver solder, and retap again, now following the good threads I'd established at 6 and 12. That job would outlast the bike.

The other option if the bike has ISO (British) threads, is to source an Italian BB (thread, not country of origin) tap the frame Italian (no ovalizing needed) and be as good as new (or at least a new Italian bike).

There may be other options if there's still enough metal at the right diameter, but it depends on the amount of material available and the type of tap the shop has.

The cups should not have play. The bottom bracket itself might have, until tightened by the cups. Since Bare Knuckle track frames are built by an Italian frame builder http://www.labrakeless.com/collectio...frame-fork-set the threadening of the BB-cups might be Italian (however, I don't know for sure). Italian style R-threaded adjustable BB-cups often loosen (particularly if it is not the original factory install anymore, or never was); a similar effect might happen here.
In contrast to FBinNY I think torque plays a role here and I would consider using thread lock on the right cup and tighten both as much as the aluminum (of the cup) allows.

My comment was based on the OPs description of it as an adjustable cup (which it turns out not to be). This type of BB needs to be torqued properly, which might account for it getting loose.

But it's the riding with loose that caused the thread damage. It's analogous to loose cotterless cranks, which are easily tightened, unless the owner rides them loose for any length of time.

Ok thanks a lot everyone for the help. I've really been freaking out about possibly losing the frame but it seems like things could be ok. The bb is english threaded. I took a measure with my calipers on the Inside Diameter of the shell and its roughly 33.85mm at the 6 and 12 position and 34.25mm at the 3 and 9. I'm not sure what the tolerance is for bb shells but this seems a little much. I'm going to bring it to a few shops this week and get some estimates/opinions.

Just because your BB is coming loose is no reason to jump to the conclusion the the BB shell is somehow to blame. Threading aluminum cups into a steel frame, even if it's done wrong will normally do no harm the steel threads. The usual suspect is you; ie user error. Miche BB have a reputation for coming loose if not installed correctly. In order to properly install the Miche BB it is recommend you use clean grease or Teflon tape (some shop mechanics use blue loctite, but the Teflon seems to be the most popular). Prior to anything you need to scrub the BB shell threads to make sure they are clean. The Miche BB has an adjustable chainline, so you need to adjust the drive side cup to the desired location and then tighten the non-drive side to about 25 f/lbs. Next tighten the driveside to about 50 ft/lbs and then do the same on the non-drive side. You must be careful as the cup installation/removal splines are very shallow and strip out easily; especially when your trying to torque in the 50 ft/lbs range. At the very least you should try a conventional BB with a drive side non-movable cup such as Origin8, SKF or Campagnolo Veloce; it would be a shame to pay hundreds of dollars to modify your bikes BB, when all you needed was a new $35 BB..

I guess i should be more detailed but when I installed them originally, I used teflon tape and torqued to same spec you mentioned. This lasted a little over a year until a few days ago. I understand that the cups need to be tightened to not become loose but is it normal for the cups to have a certain amount of play in the bb shell? I estimate there is .5-1mm of play where I can wiggle the cups inside the shell. Only until are they are fully tightened is there not play.

My assumption was that even if the cups are not fully tightened in the shell I shouldn't be able to wiggle them inside the cups. The threads still engage and I can still tighten the cups to spec but I just worry about the amount of play when they are loose in the BB shell. Is this normal?

I did a quick check with a caliper and found the Miche cups measure about 29.5mm where other BB cups average out at 29.8 (this included two adjustable chainline BB; Phil Wood and Raceface ST). What you should keep in mind is the Miche system is not the most secure. Phil Wood uses a similar system but requires a thread locking compound similar to loctite, the Phil Wood compound coming in 3 different strengths; low, medium and high (if the BB comes lose with low, try medium and then high). As I said before, the drive side fixed cup style bottom bracket doesn't have this problem and doesn't require any locking compound. You should keep in mind that if your BB shell was ovalised it would normally fit tighter, not come loose. If one starts with the fact the the Miche cups are .3mm smaller in diameter than other BB cups and the Miche BB cups are rattling around in the shell, wouldn't it make sense to try a BB with larger cups? My diagnosing process always starts with the most obvious or cheapists solution and then moves on the more expensive solutions. The cheapists solution would be to warp the teflon tape thicker than before. Next, Loctite is cheap, so I would would try some Loctite (the surfaces have to be absolutely clean for this to work) and if it doesn't work, try another BB.

onespeedbiker, I completely agree. A colleague and I have pretty much come to the same conclusion as you and have deduced that it's the cups themselves and not the bb shell. We are going to check some various other 68mm cups tomorrow and see if the fit is the same.

If it is just the cups then that's great! But my next question would be whether to

A. stick with this bottom bracket and use Loctite (already tried teflon with no success)

or

B. get a new bb and crankset (miche propitiatory sizing greatly limits bb selection).

I'm unsure about the loctite as I would hate the possibility of it seizing and ruining the threads later on during service.

Can anyone recommend a 68mm x 107mm English threaded iso taper bb? I have yet to find one.

Could chase the frame threads with the BB tap set and make sure it's not the frame.

Measuring the OD of a thread is an almost meaningless exercise. Threads engage on the flanks not the peaks so you need to measure what's called the pitch diameter. A process that uses either a special micrometer that touches the flanks without touching the crests or roots. Pitch diameter can also be measured using wire of a known diameter and a chart to translate the results.

Note that threads are rarely 100%, and the crests are often truncated by varying amounts, but this doesn't affect the fit, something which depends on the pitch diameter, which few bike mechanics have any idea of how to measure.

As a practical matter, a decent mechanic can check your BB shell's threads by way of a crude gauge, ie a known to fit well BB cup, which he can thread in and check for radial play. Likewise your Miche rings can be checked the same way in another new frame. Radial play in BB threads used to be rare, but has become more common over the last few decades, especially among what I'd call B-class makers. But even among A class produces like Campy and Shimano Dura Ace, there's also variation with Campy generally having a tighter fit. Given the quality level, I suspect that it isn't an issue of sloppiness, but where within the standard tolerance they set their targets.

Even perfect threads can sometimes seem sloppy, and my preferred way to build them up for a tighter, no creak fit is to paint one or the other with nylon paint. This makes a tight fit controlled by the thickness of the nylon, while still allowing dis-assembly later

The obvious answer IMHO is to try the loctite; I have used blue loctite on several occasions with good results and the screw was easy to remove later.

Obviously you could get a Phil Wood in any size, but I would think the price would place it out of your range. Soma sells a Tange 109 that should work http://store.somafab.com/taisosqtabob.html; assuming it's symetrical or; you could also buy a BB with a smaller spindle like this 103 IRD http://harriscyclery.net/product/ird...pered-2942.htm and space it out 2mm

So I just checked the fit with a Dura Ace Bottom bracket. The slop is definitely due to the Miche bb! The Dura Ace bb fit snug and proper.

After seeing how another bb fit the shell so well its amazing how loose the Miche is.

Probably going to look into a different bb/crankset setup. I was looking into replacing the cranks anyways since they are the old Miche style with the threaded spider and 135bcd.

Thanks for the help everyone!