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rechasing stripped bottom bracket
just started volunteering at a bike exchange near me at the Boys/Girls club
someone donated a 1996 Cannondale SR500 (the purple one with a headshok) but it has stripped threads on the non-drive side of the bottom bracket Should I attempt to rechase the threads using steel cups? We don't have chasing tools so that may be my only option. Fine with just dumping the frame, but if I can get it back to a safe riding condition, the bike may bring $200-300 to the club |
Chasing can correct damaged threads, such as when there was some cross-threading. But it can't magically restore metal that's not there in a stripped thread. If it's truly stripped, such that it can't hold a cup, then the only option is tapping bigger. BITD it was common to convert stripped 1.37" BSC bottom brackets to Italian it involves real tools, and is rarely done anymore.
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The Proper BB thread cutting tool is special to bicycle Manufacturing . it has a Guide pin so both threads are in alignment precisely.. Park Tool Co. » BTS-1 : Bottom Bracket Tapping & Facing Set : Frame & Fork Tools
(as a Charity with valid 501c3 status you may be able to offer a Tax write down to a Bike shops Business accounting , to get the Shop to do the work with the proper tool.) A BB which does Not Use the threads was made and is sold by Velo Orange Grand Cru Threadless Bottom Bracket - Bottom Brackets - Components on the cheap and not fixing the problem .. but making it function.. the shimano UN type BB with a plastic Left sleeve at least wont make things worse .. an Epoxy filler, cured. then cut with the BB tap, may replace lost metal somewhat .. [JB weld has aluminum, Powdered, in its resin Portion] at least disclose the damage and be willing sell the bike, with that information, for Less . |
The Velo Orange option is the best in your circumstance if the threads are stripped, but you need to make sure you get the proper length. If damaged or cross threaded a cup is not at all the proper tool. Have a bike shop chase the threads with a tap.
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the VO option appears to be the ideal option, but I'm sure there are no funds available to go that route
The previous owner did use the epoxy UN cup option, but should I try it again? Safety is my primary concern, even if we disclose it as a known issue. I'll also check with some LBS for opinions on rechasing feasibility and the non-profit write off (that's a great idea Bob) |
i can't see any downside, IMO, to just trying it. it may or may not work is all.
but i would be compelled to tell a potential buyer what i had done, and so wouldn't hold out much hope of selling it at the price mentioned. i say that becuase, recently i have purchased a couple of nice new bare frames that, IMO, are every bit as good at 89 a piece. |
Originally Posted by qclabrat
(Post 17463129)
the VO option appears to be the ideal option, but I'm sure there are no funds available to go that route
The previous owner did use the epoxy UN cup option, but should I try it again? Safety is my primary concern, even if we disclose it as a known issue. I'll also check with some LBS for opinions on rechasing feasibility and the non-profit write off (that's a great idea Bob) |
I really don't like the threadless 'problem solver' type BBs. They put enormous tension on the BB shell. Since the NDS threads aren't required for torquing the BB cartridge laterally against the BB face (that cup simply there to center the cartridge along its axis), I'd prefer to have a shop chase the threads (and the DS threads while they're at it) and then install a Shimano UN55 cartridge for $25. Since the DS threads are fine, the unit should be very reliable.
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AGAIN, it's not clear yet whether the threads are in good enough shape to be chased and reused. The OP is taking it to a shop to determine that. If they are stripped out then there are no threads to chase. As far as the "enormous tension," the BB shell is by far the beefiest part of the frame, so the compression tension on it from such a BB is relatively minor
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If here are no funds available to pay for shop labor or replacement parts, I'd consider selling it As-Is, as a frameset with the notice that it has a problem with the bottom bracket, needs professional repair (to by paid for by the Buyer), AND the agreement that the cost of the frame would be refundable with a written letter from a shop stating that the frame had been inspected, could not be repaired.
That way the Coop still gains a little money, the frame is saved if possible, and the Buyer knows exactly what he/she is getting. |
Originally Posted by RoadGuy
(Post 17463722)
If here are no funds available to pay for shop labor or replacement parts, I'd consider selling it As-Is, as a frameset with the notice that it has a problem with the bottom bracket, needs professional repair (to by paid for by the Buyer), AND the agreement that the cost of the frame would be refundable with a written letter from a shop stating that the frame had been inspected, could not be repaired.
That way the Coop still gains a little money, the frame is saved if possible, and the Buyer knows exactly what he/she is getting. |
Can someone tell me what the typical cost is to re-chase one side of a shell? And is that something most shops can do? Or do I need to find a frame builder?
I just found I broke my fixed cup (Drive side) - it sheared along the outer cup threads. I tried threading the cup back in and it feels a bit rough...I think it looks like it's screwing in cock-eyed, but hard to tell. A new cup might work fine, or I may have stripped the shell threads a bit (I rode it a few days with the fixed cup working its way out a couple of turns). It's an old 501 reynolds steel frame, I was going to look for a bargain parts bin cup at the shop and failing that just pick up a cheap sealed Shimano BB. This is just an old 80s bike I use for commuting and street lock up so I want to keep costs down... |
...those Cannondale headshocks are quite notorious for failure in their own right, and Cannondale stopped supporting them.
Don't toss good money/effort into this bike, just pull and sell the components as a group, and recycle it for beer cans. |
Well this is a bit of a necro, but you can rebuild threads and add material that was removed with products like form-a-thread. At the very least it's probably stronger than plastic cups on some cartridge BBs.
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Originally Posted by pgoat
(Post 18929593)
Can someone tell me what the typical cost is to re-chase one side of a shell? And is that something most shops can do? Or do I need to find a frame builder?
I just found I broke my fixed cup (Drive side) - it sheared along the outer cup threads. I tried threading the cup back in and it feels a bit rough...I think it looks like it's screwing in cock-eyed, but hard to tell. A new cup might work fine, or I may have stripped the shell threads a bit (I rode it a few days with the fixed cup working its way out a couple of turns). It's an old 501 reynolds steel frame, I was going to look for a bargain parts bin cup at the shop and failing that just pick up a cheap sealed Shimano BB. This is just an old 80s bike I use for commuting and street lock up so I want to keep costs down... If you've removed the cup already and have not cross threaded a replacement cup, it's a straightforward job which shouldn't cost much at all, and probably isn't necessary anyway. OTOH if it's now cross threaded thanks to your earlier efforts, it my be much more complicated, and I won't venture a guess without seeing it. I know a large percentage of NYC dealers (4 boroughs) and might be able to refer you to someone good if you send me a PM telling me where you live. |
Originally Posted by pgoat
(Post 18929593)
Can someone tell me what the typical cost is to re-chase one side of a shell? And is that something most shops can do? Or do I need to find a frame builder?
I just found I broke my fixed cup (Drive side) - it sheared along the outer cup threads. I tried threading the cup back in and it feels a bit rough...I think it looks like it's screwing in cock-eyed, but hard to tell. A new cup might work fine, or I may have stripped the shell threads a bit (I rode it a few days with the fixed cup working its way out a couple of turns). It's an old 501 reynolds steel frame, I was going to look for a bargain parts bin cup at the shop and failing that just pick up a cheap sealed Shimano BB. This is just an old 80s bike I use for commuting and street lock up so I want to keep costs down... Loose ball cups can crack around the ball track after many miles of abuse, and an incorrectly adjusted Bb is abuse. The ones I usually see can be unthreaded from the shell with standard cup tools. Rarely the cup's end will completely separate from the threaded portion. The shell's threads are usually not badly harmed. The cup will become distorted after cracking, the end will look cocked WRT the threaded portion. Trying to reuse or even reinstall a cracked cup is bad decision making. When chasing a BB shell threads it is very important to maintain the shell's sides' coaxialness. So only chasing one side without the other side's tap in place, and support the pilot shaft, is another example of poor decision making. If a shop or builder is willing to only run one side's tap through the shell then question their experience. It is very easy with such a large diameter but fine pitch tap to miss align the threads and cut across the OEM threads. Andy. |
Originally Posted by 2lo8
(Post 18929792)
Well this is a bit of a necro, ...
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Assuming my BB shell threads are okay, I was looking at a Shimano UN with plastic cup, to keep costs down:
https://www.amazon.com/gp/product/B0...=AMY4I718ZUBOU or, if the threads are shot, rather than pay a shop to mess with it (which may not work anyway) and a new BB...any opinions on how well these work? https://www.sjscycles.co.uk/bottom-b...reads/?geoc=US |
Originally Posted by Andrew R Stewart
(Post 18929815)
Loose ball cups can crack around the ball track after many miles of abuse, and an incorrectly adjusted Bb is abuse. The ones I usually see can be unthreaded from the shell with standard cup tools. Rarely the cup's end will completely separate from the threaded portion. The shell's threads are usually not badly harmed.
Thanks for this info, Andy, and I hope you're right - visually the threads look bit shallower to me, but they might still have enough bite for a new BB. I can only guess that I cross-threaded the cup the last time I o/h the BB (about three months ago). Idk how that happened, I've done this a zillion times on a variety of bikes with different cups and tools and never had an issue before. Maybe I was rushing or distracted that day, idk. The cup will become distorted after cracking, the end will look cocked WRT the threaded portion. Trying to reuse or even reinstall a cracked cup is bad decision making. I realize what I saw as cockeyed screwing the old broken cup back in was at least partially due to the flange of the cup being off-kilter. But I think the resistance I felt and some wonky movement tells me there's some BB shell damage also. I only screwed the old cup in until it felt rough, then backed out and removed it. I sprayed the shell with WD40 first and wiped it down as best I could. When chasing a BB shell threads it is very important to maintain the shell's sides' coaxialness. So only chasing one side without the other side's tap in place, and support the pilot shaft, is another example of poor decision making. If a shop or builder is willing to only run one side's tap through the shell then question their experience. It is very easy with such a large diameter but fine pitch tap to miss align the threads and cut across the OEM threads. Andy. |
Happy to say my go-to shop here had an old fixed cup they gave me for free. I bought some new loose bearings and am gonna see how she looks after dinner tonight...fingers crossed the frame is okay.
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Finally had a second to follow up - the fixed cup they gave me fit just fine; after cleaning up the cup and inside of the BB shell I found the frame's threads were noticeably worn near the outer edge. But I took care to screw in the cup straight and used a little teflon tape on the cup's threads, and it went in good and snug. After a few weeks of commuting, no problems, I'm happy to say.
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The Other real Solution is Brass , you Lose the paint job
but by Thoroughly cleaning the Inside of the BB shell , and brazing in metal where the threads are gone then Re threading the now Brass lined steel BB shell and repainting it , it will be quite serviceable Again .. If you have to ask ''Is it worth it?", then, no , It probably Isn't. |
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