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JIS Standard Vs "Low Profile" crank tapers
I have an old bike long since converted to a "fixie". He's a solid
old machine with well over 100K behind him. The original "cup & cone" BB is simply worn out. It's worth a new BB to get it back on the road, IMO. My issue is that I currently have the old "JIS Low Profile" taper. I suppose that I can replace the crank, but I'd prefer not to. If I go to a standard square JIS taper, will my current crank work? My LBS says it will; however, I'm not impressed with their knowledge of obsolete (or "antique", depending on your interpretation) parts. It looks to me like the JIS low profile taper is identical to the JIS standard one at the tapered end; however, the low profile taper ends prematurely in a shoulder. If this is true, then the crank with a low profile taper would fit on to the end of the standard taper just fine; however, this would push the chain line outboard... I'm going to guess about 2mm on each side. Does anyone have first-hand experience? Jones... who seeks but to serve God... and to grow wealthy, of course, as all men. |
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#2
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JIS Standard Vs "Low Profile" crank tapers
!Jones wrote:
I have an old bike long since converted to a "fixie". *He's a solid old machine with well over 100K behind him. *The original "cup & cone" BB is simply worn out. It's worth a new BB to get it back on the road, IMO. *My issue is that I currently have the old "JIS Low Profile" taper. *I suppose that I can replace the crank, but I'd prefer not to. [...] It looks to me like the JIS low profile taper is identical to the JIS standard one at the tapered end; however, the low profile taper ends prematurely in a shoulder. *If this is true, then the crank with a low profile taper would fit on to the end of the standard taper just fine; however, this would push the chain line outboard... I'm going to guess about 2mm on each side. If there is no feature on your cranks that would stop them from being tightened before they attain a full interference fit on the spindle taper, then just get a normal JIS bottom bracket and install everything. If your cranks were sitting hard against the shoulder before, they'll probably push in just a little father on a non- shouldered spindle. For what it's worth, the Shimano BB-UN26 has press-fitted collars that serve as stops/shoulders (I sometimes remove them), and it costs about $15. I install these all the time and there have been no unusual problems with them. Chalo |
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JIS Standard Vs "Low Profile" crank tapers
On Apr 1, 5:29*pm, Chalo wrote:
For what it's worth, the Shimano BB-UN26 has press-fitted collars that serve as stops/shoulders (I sometimes remove them), and it costs about $15. *I install these all the time and there have been no unusual problems with them. The UN26 is an interesting bottom bracket, found as standard on a whole bunch of prestigious and pricey bikes, starting with Gazelle and relations, like Koga-Miyata. Utopia and other prestigious German makers are very keen on the even less expensive Kinex bottom bracket. These are people who have independent tests done on everything that goes on their bike, and give a ten-year guarantee. So it looks for all the world as if these experienced manufacturers decided that the bottom bracket is such a mature technology that there is zero advantage in splashing out even one step up from the base model by a reputable manufacturer. In short, the bottom bracket is a commodity item. -- Andre Jute |
#4
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JIS Standard Vs "Low Profile" crank tapers
On Apr 1, 5:00*pm, "!Jones" wrote:
I have an old bike long since converted to a "fixie". *He's a solid old machine with well over 100K behind him. *The original "cup & cone" BB is simply worn out. It's worth a new BB to get it back on the road, IMO. *My issue is that I currently have the old "JIS Low Profile" taper. *I suppose that I can replace the crank, but I'd prefer not to. If I go to a standard square JIS taper, will my current crank work? My LBS says it will; however, I'm not impressed with their knowledge of obsolete (or "antique", depending on your interpretation) parts. It looks to me like the JIS low profile taper is identical to the JIS standard one at the tapered end; however, the low profile taper ends prematurely in a shoulder. *If this is true, then the crank with a low profile taper would fit on to the end of the standard taper just fine; however, this would push the chain line outboard... I'm going to guess about 2mm on each side. Does anyone have first-hand experience? Jones... who seeks but to serve God... and to grow wealthy, of course, as all men. Yo, Jones, reference to Sheldon Brown's pages will tell you exactly how far your chain line will move when you switch between crank axle tapers without changing cranks. I looked into it once, and IIRC, it was only about 1mm per side, not enough to disturb even a finicky Rohloff setup. Kinex bottom brackets offer various tapers and are inexpensive and good. No idea where you will get them in the States. And don't Campagnolo bottom brackets come with the taper you want; over here their lower end BB are sometimes under thirty euro on sale. -- Andre Jute |
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