Bottom Bracket Upgrade
09-09-21, 02:47 PM
#26
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No argument regarding using a chaser to restore the threads if compromised, and I wasn't implying that your advise wasn't sound. I'm also certain you could restore the threads if they're damaged. (Not sure if I could or not, never had to do it so I haven't tried.)
But if the OP (1) indeed has a Swiss-threaded BB shell, (2) can't find another Swiss BB (or can't afford a Phil Wood BB, which I understand can still be had with Swiss cups), and (3) can't restore his current BB to usefulness, he may be left with precious few other options if he wants to keep using the frame. One of those options would be to use a repair/threadless BB.
My intent was simply to highlight one potential "gotcha" if using a repair/threadless bottom bracket: it's very likely available in JIS square taper only. You're IMO likely correct that that limitation won't be a problem. I've always thought it best to know about a possible issue in advance and make an informed decision regarding accepting a potential risk, even if that risk is small.
But if the OP (1) indeed has a Swiss-threaded BB shell, (2) can't find another Swiss BB (or can't afford a Phil Wood BB, which I understand can still be had with Swiss cups), and (3) can't restore his current BB to usefulness, he may be left with precious few other options if he wants to keep using the frame. One of those options would be to use a repair/threadless BB.
My intent was simply to highlight one potential "gotcha" if using a repair/threadless bottom bracket: it's very likely available in JIS square taper only. You're IMO likely correct that that limitation won't be a problem. I've always thought it best to know about a possible issue in advance and make an informed decision regarding accepting a potential risk, even if that risk is small.
Going in with delusions of grandeur and success are a surefire way to insure you may experience neither.
Be careful and realistic, play to your strengths, know when you really need the proper tool before you muck it up since after the fact it may not save you.
09-09-21, 03:35 PM
#27
Full Member
If the frame is indeed Swiss-threaded (and reputedly at least some Motobecanes of that era were), you may be out of luck in finding a new bottom bracket at all - particularly if you're looking for a modern external-cup version. My understanding is that that BB standard is now completely obsolete and was also rare even 30-40 years ago. But perhaps someone with more knowledge than I on this forum can point you at a source.
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09-09-21, 03:39 PM
#28
Senior Member
Unfortunately, that won't help the OP with his desire to use a large-spindle SRAM crank. But it does give him another option besides a threadless BB or rehabbing his current BB.
09-09-21, 03:49 PM
#29
Full Member
Thanks. I figured someone here would know whether such a product was still currently made or not (other than possibly by Phil Wood).
Unfortunately, that won't help the OP with his desire to use a large-spindle SRAM crank. But it does give him another option besides a threadless BB or rehabbing his current BB.
Unfortunately, that won't help the OP with his desire to use a large-spindle SRAM crank. But it does give him another option besides a threadless BB or rehabbing his current BB.
For the OP's situation, if it were Swiss, then I would look to Phil Wood. I see Swiss / GXP there for $184/set, but they show as sold out at the moment.
Last edited by John Valuk; 09-09-21 at 06:48 PM.
09-09-21, 04:56 PM
#30
Member
Thread Starter
As I don't have any tool to make a chaser, I took the old cups to the local bike shop to ask for the cuts on the cups; They told me that the old cups are English threaded. As they were excited to see a four-decade old Motobecane, they offered free threading of the BB shell (and they said everything is OK, just that the bike is very old and perhaps the BB hasn't been touched for decades).
I just installed the two cups: the drive side is tight, but the non-drive side has still a tiny gap after putting enough force to tighten it (see the photo). Any thoughts if this gap is OK? The BB came with two spacers, though everywhere in the net that I checked says the spacers are not needed (68mm BB). Does anybody recommend using them? Or maybe only one for the non-drive side with the tiny gap? I installed the Sram Rival crankset and everything seems to be fine.
I just installed the two cups: the drive side is tight, but the non-drive side has still a tiny gap after putting enough force to tighten it (see the photo). Any thoughts if this gap is OK? The BB came with two spacers, though everywhere in the net that I checked says the spacers are not needed (68mm BB). Does anybody recommend using them? Or maybe only one for the non-drive side with the tiny gap? I installed the Sram Rival crankset and everything seems to be fine.
09-09-21, 06:13 PM
#31
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As I don't have any tool to make a chaser, I took the old cups to the local bike shop to ask for the cuts on the cups; They told me that the old cups are English threaded. As they were excited to see a four-decade old Motobecane, they offered free threading of the BB shell (and they said everything is OK, just that the bike is very old and perhaps the BB hasn't been touched for decades).
I just installed the two cups: the drive side is tight, but the non-drive side has still a tiny gap after putting enough force to tighten it (see the photo). Any thoughts if this gap is OK? The BB came with two spacers, though everywhere in the net that I checked says the spacers are not needed (68mm BB). Does anybody recommend using them? Or maybe only one for the non-drive side with the tiny gap? I installed the Sram Rival crankset and everything seems to be fine.
I just installed the two cups: the drive side is tight, but the non-drive side has still a tiny gap after putting enough force to tighten it (see the photo). Any thoughts if this gap is OK? The BB came with two spacers, though everywhere in the net that I checked says the spacers are not needed (68mm BB). Does anybody recommend using them? Or maybe only one for the non-drive side with the tiny gap? I installed the Sram Rival crankset and everything seems to be fine.
'Chasing' actually re-cuts the threads... cleanly... takes away burrs, dirt and rust on older BB...
If you feel comfortable with where you are now - I would add a 'spacer' between non-drive cup and BB, spacer just a hair thicker than the remaining space...
Point is its Better to be able to snug down the cup before you try to 'force' it further... You could damage ALL the threading if you force past this point...
If the threading becomes damaged, it may 'strip' in use. Cups are alloy, after all....
Important to have the cup supported/snugged against the BB shell exterior to prevent eventual distortion and rocking of the cup...
Thx
Yuri
EDIT: I'm assuming that the non-drive crankarm is not fully seated, because you haven't seated it fully, yet...
Last edited by cyclezen; 09-09-21 at 06:17 PM.
09-09-21, 07:32 PM
#32
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As I don't have any tool to make a chaser, I took the old cups to the local bike shop to ask for the cuts on the cups; They told me that the old cups are English threaded. As they were excited to see a four-decade old Motobecane, they offered free threading of the BB shell (and they said everything is OK, just that the bike is very old and perhaps the BB hasn't been touched for decades).
I just installed the two cups: the drive side is tight, but the non-drive side has still a tiny gap after putting enough force to tighten it (see the photo). Any thoughts if this gap is OK? The BB came with two spacers, though everywhere in the net that I checked says the spacers are not needed (68mm BB). Does anybody recommend using them? Or maybe only one for the non-drive side with the tiny gap? I installed the Sram Rival crankset and everything seems to be fine.
I just installed the two cups: the drive side is tight, but the non-drive side has still a tiny gap after putting enough force to tighten it (see the photo). Any thoughts if this gap is OK? The BB came with two spacers, though everywhere in the net that I checked says the spacers are not needed (68mm BB). Does anybody recommend using them? Or maybe only one for the non-drive side with the tiny gap? I installed the Sram Rival crankset and everything seems to be fine.
09-10-21, 06:30 AM
#33
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Sometimes the marks are somewhat arcane; rather than explicitly stating the thread spec, cup shape, presence or absence of rings, etc. were used to indicate thread spec:
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