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#11
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Threadless BB Cartridges: Why/Why Not?
Tom Sherman writes:
Thanks to Werehatrack for introducing me to the concept... Now it begs the question: Why are BB shells threaded in the first place? i.e. Why don't most bikes just come with threadless already installed? Sounds like there's a downside... I must have missed it but could you direct me to a web site where I can see the cross section of a threadless BB? The only ones I know of were on Ashtabula cranks and they had a larger diameter. Surely, you recall the Mavic system of the eigties? Conical rings on both sides screw onto a threaded Phil-ish cartridge. IN Mavic's design, the frame gets milled with a 4mm chamfer on each end of the BB. The later all-nylon-casing types (KSS brand) seem to work fine without that chamfer. I don't recall, and don't call me Shirley. They are both more expensive to make and much more time consuming to install. As such they can't be an OEM part and in today's world that is a kiss of death. Low volume means high prices which leads to low volume and therefore high prices, etc. Picture reference please. I don't have much hope though because these folks seldom show a cross section drawing where the function is revealed. You might suspect they don't trust their patent protection. Is this the referenced BB? See http://www.bikepro.com/products/bott...ets/mavic.html Insterding! Just the outer picture leaves me wondering what else they didn't test. At least the text explains what the intent was. In this design, the tube pictured is centered on threads that Mavic hoped would be radially clearance free, unlike standard BB cups. I don't believe that is a reasonable supposition unless the conical rings had at least two splits to allow them to clamp, as my pedal attachments do. What's worse is that there is no explanation of how the spindle is secured in the bearings and what sort of bearings these are. Just to give an idea of the fragility of BB retention, I recently had the right hand cup loosen and not be tightenable. When I removed it, I discovered that more than 100000 miles of riding had eroded the threads from the steel BB shell. The right side thread was completely gone and the left side close behind. The right hand cup had been brutally tightened and never removed during that time. Fretting gradually ate up the threads leaving nothing but grey paste. My frame maker bored the BB shell and silver soldered in steel threaded sleeves abut 12mm deep on either side. It is from this sort of experiences that I am suspicious of the Shimano over-hung BB bearing design. How can that work even nearly as well as internal BB cups? Jobst Brandt |
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#12
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Threadless BB Cartridges: Why/Why Not?
On Fri, 24 Feb 2006 14:03:24 -0500, "(PeteCresswell)"
wrote: Thanks to Werehatrack for introducing me to the concept... Now it begs the question: Why are BB shells threaded in the first place? i.e. Why don't most bikes just come with threadless already installed? Sounds like there's a downside... Most prevalent downside at present is the difficulty of getting a good one for a reasonable price. Bike Tools Etc sells one made by YST, but it's been disparaged for its relatively low durability. OTOH, at $17 plus shipping, it's one way to get a frame back in service quickly when the threads have been damaged, and even if it only has a lifetime of a couple of years in moderate service, that might be acceptable to many riders. -- Typoes are a feature, not a bug. Some gardening required to reply via email. Words processed in a facility that contains nuts. |
#13
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Threadless BB Cartridges: Why/Why Not?
So far as I have known, the Mavic thread less BB cartage was for fixing
stripped out threads, when the bike owner didn't want to spend enough $$$ to mill out the BB (frame) & re-thread for an Italian BB. Or the frame already had an Italian BB. I've (correctly/incorrectly) thought it was an inferior fix it terms of long-term reliability. And that JIS version was even poorer. John |
#14
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Threadless BB Cartridges: Why/Why Not?
J. Brandt wrote:
Just to give an idea of the fragility of BB retention, I recently had the right hand cup loosen and not be tightenable. When I removed it, I discovered that more than 100000 miles of riding had eroded the threads from the steel BB shell. The right side thread was completely gone and the left side close behind. The right hand cup had been brutally tightened and never removed during that time. Fretting gradually ate up the threads leaving nothing but grey paste. Jobst I don't see how you can seriously use the terms "fragility" & "100,000 miles" in the same paragraph. It would probably take a pile of 100 bikes @ a scrap yard, to have acclimated that kind of mileage or a pile of 10 bikes of the average rbt reader :/) John |
#15
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Threadless BB Cartridges: Why/Why Not?
Johnny Sunset aka Tom Sherman wrote: Is this the referenced BB? See http://www.bikepro.com/products/bottom_brackets/mavic.html. Yes. Here's a slightly better pictu http://www.zefal.com/stronglight/pag...keyProd=jp1000 "JP 1000". This photo almost shows the beveled tightening rings (alloy) *and* the thin plastic washers that fit in between the rings and the chamfered BB shell. Also almost shown, the outer, threaded adjustable (pin spanner), cicular alloy side plates, approx. 6mm thick, with o-ring around the outer circumference, but not the inner, where the axle pokes through. Roller bearings ride on shoulders on the crank axle. I've used a bike thus equipped for awhile, seems to work ok in spite of a lack of axle shaft seal-- maybe some Campy-style threads in there would be good; of course that would make it even more expensive. I don't think they sell for more than other cart. BB setups, though I haven't checked prices in awhile. Seems like a pretty good solution, maybe analagous to conical fit between crank (arm) and pedal spindle. --D-y |
#16
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Threadless BB Cartridges: Why/Why Not?
In article ,
wrote: Just to give an idea of the fragility of BB retention, I recently had the right hand cup loosen and not be tightenable. When I removed it, I discovered that more than 100000 miles of riding had eroded the threads from the steel BB shell. The right side thread was completely gone and the left side close behind. The right hand cup had been brutally tightened and never removed during that time. Fretting gradually ate up the threads leaving nothing but grey paste. One idea I've considered is to have a bottom bracket shell cut across the bottom, and clamp lugs (like seatpost clamp ears) across the cut, or perhaps external clamps outside each cup. This would allow the BB shell to be clamped down on the cups and arrest this fretting. I'm not sure how good my intuition is for the magnitude of forces encountered here, but the existance of bottom brackets with extensive cutouts suggests to me this may be reasonable. The torsion coming from the downtube would be the same order as what the handlebar clamp supports, and this is a much larger interface which should support it easily. On the other hand, vertical pedalling loads and chain tension that the handlebars don't experience, would be acting here. I think the chain tension would be benign though, being in a direction that wouldn't act to open this split. Vertical loads, I don't expect to be an issue as long as the clamping is intact, but would be an issue with a clamp bolt failure. I'm not sure that the BB cups are wide enough to allow for redundant clamping here. -Luns |
#17
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Threadless BB Cartridges: Why/Why Not?
john Drew writes:
Just to give an idea of the fragility of BB retention, I recently had the right hand cup loosen and not be tightenable. When I removed it, I discovered that more than 100000 miles of riding had eroded the threads from the steel BB shell. The right side thread was completely gone and the left side close behind. The right hand cup had been brutally tightened and never removed during that time. Fretting gradually ate up the threads leaving nothing but grey paste. I don't see how you can seriously use the terms "fragility" & "100,000 miles" in the same paragraph. It would probably take a pile of 100 bikes @ a scrap yard, to have acclimated that kind of mileage or a pile of 10 bikes of the average RBT reader :/) The people with whom I ride often total more than 10,000 miles per year as I have. My Campagnolo hubs from the 1970's are still serving well and I expect the frame to retain its "static" BB threads at least as well. The point is that crank threads and BB threads are dynamic and constantly moving, although they shouldn't. That is why left hand threads are used there. If you ask why we have left hand threads, most shops will mater-of-fact tell you so they don't unscrew. If you then ask why these threads aren't tightened, you will get a blank stare. Of course we tighten them is the reply. So how do they unscrew? These are classically improper designs and I don't believe anyone has attacked the BB problem although I have modified my cranks so that pedal threads don't move and cause crank failures of which I had many. I no longer need left hand threads on the left pedals. Because right threaded left cranks are rare and right-right pedal pairs even rarer, I still use left threaded left pedals. Jobst Brandt |
#18
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Threadless BB Cartridges: Why/Why Not?
someone writes:
Is this the referenced BB? See http://www.bikepro.com/products/bottom_brackets/mavic.html. Yes. Here's a slightly better pictu http://www.zefal.com/stronglight/pag...keyProd=jp1000 "JP 1000". This photo almost shows the beveled tightening rings (alloy) *and* the thin plastic washers that fit in between the rings and the chamfered BB shell. Also almost shown, the outer, threaded adjustable (pin spanner), circular alloy side plates, approx. 6mm thick, with o-ring around the outer circumference, but not the inner, where the axle pokes through. Roller bearings ride on shoulders on the crank axle. I've used a bike thus equipped for awhile, seems to work OK in spite of a lack of axle shaft seal-- maybe some Campy-style threads in there would be good; of course that would make it even more expensive. I see no additional information in this picture and don't believe it addresses the problem at all, other than give the user a second chance for BB treads to fail. The second time faster, because they are finer. I don't think they sell for more than other cart. BB setups, though I haven't checked prices in awhile. Seems like a pretty good solution, maybe analogous to conical fit between crank (arm) and pedal spindle. --D-y Not at all. I see no press fit between the threaded cylinder and the conical centering rings. Besides, how is the spindle retained and how are the bearings held in the tube? Both of these present greater fretting problems than a conventional cup BB. Jobst Brandt |
#19
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Threadless BB Cartridges: Why/Why Not?
Luns Tee writes:
Just to give an idea of the fragility of BB retention, I recently had the right hand cup loosen and not be tightenable. When I removed it, I discovered that more than 100000 miles of riding had eroded the threads from the steel BB shell. The right side thread was completely gone and the left side close behind. The right hand cup had been brutally tightened and never removed during that time. Fretting gradually ate up the threads leaving nothing but grey paste. One idea I've considered is to have a bottom bracket shell cut across the bottom, and clamp lugs (like seatpost clamp ears) across the cut, or perhaps external clamps outside each cup. This would allow the BB shell to be clamped down on the cups and arrest this fretting. That is an idea. but that makes the BB an open sided tube that has no torsional strength, and there is a rotating force there or the right hand cup wouldn't need a left thread. I'm not sure how good my intuition is for the magnitude of forces encountered here, but the existence of bottom brackets with extensive cutouts suggests to me this may be reasonable. The torsion coming from the downtube would be the same order as what the handlebar clamp supports, and this is a much larger interface which should support it easily. On the other hand, vertical pedaling loads and chain tension that the handlebars don't experience, would be acting here. I think the chain tension would be benign though, being in a direction that wouldn't act to open this split. Cut-outs OK but not slotted crosswise. Vertical loads, I don't expect to be an issue as long as the clamping is intact, but would be an issue with a clamp bolt failure. I'm not sure that the BB cups are wide enough to allow for redundant clamping here. I'm sure that is OK, bu the forces on the shell are not so simple as they first appear judging from the need for a left thread. Jobst Brandt |
#20
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Threadless BB Cartridges: Why/Why Not?
Luns Tee wrote:
One idea I've considered is to have a bottom bracket shell cut across the bottom, and clamp lugs (like seatpost clamp ears) across the cut, or perhaps external clamps outside each cup. This would allow the BB shell to be clamped down on the cups and arrest this fretting. I have a ~30 year old frame (Belgian) that has exactly this setup. The BB shell has 2 slots with ears and pinch bolts to clamp both the fixed and adjustable cups. I assumed, given the age of this bike, it was a well-known technique. I wondered why it isn't used more often. |
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