Garth- This is excellent info. Thanks for sharing. It looks like many modern cartridge BBs still have a little drive side offset, but it differs by model.
I already ordered (and received) a 124 mm symmetric BB from Velo Orange. I'm going to take it to the bike shop tonight* and install it with some BB spacers, to approximate the original XT M730 spindle (4 mm drive side offset). That should put both sides of the crank close to their original orientation. If I can't get the VO one set up properly, I'll try the 127 mm next. It looks like that model has 2 mm of offset built in. I wonder if I would notice the extra spindle length on the non-drive side with the 127 mm BB. Tim Gavin Cedar Rapids, IA *I work part time in a LBS, so I get to wrench on my own bikes there when I'm off the clock. They may even have a 127 mm UN-55 in stock, if I need it. On Thu, Mar 19, 2015 at 7:33 AM, Garth <[email protected]> wrote: > > <https://thebikesmiths.com/uploaded/thumbnails/db_file_img_4941_500xauto.jpg> > Tim , When changing from the pre cartridge days to the present BB's it's > not always so simple as just saying "my old BB is a 124 so that's what I'll > get" . > > First of all, while JIS is a standard, different brands and models do > not always set in the crank arms the same. You may have to try multiple > brands or lengths and spacers to get it dialed in. I've found sometimes it > helps to go with a slightly longer spindle , like in your case, the 127, > because it has more inherent length on the drive side, meaning less or no > spacers at all. This may or may not lead to a few mm's extra on the left, > which is of no concern . We're talking millimeters here , not centimeters > , a few here are there are unnoticed . > > Here is the Tange BB chart, for example, it's very useful and you could > download it for keeping. I believe Shimano BB's also use these proportions > . > > On Saturday, March 14, 2015 at 8:32:22 PM UTC-4, Tim Gavin wrote: >> >> While riding yesterday, I noticed that my cranks were wobbling. I >> stopped in the nearest bike shop (since I was not in my home town) to see >> if I could just tighten it up quickly. The tech tried that and found that >> the bottom bracket was shot: the cups have worn too much. >> >> Thankfully, he didn't charge me anything since he didn't do much. But >> it's something I could have figured out easily myself, if only I'd noticed >> the wobble while at home. >> >> It felt secure and strong as I commuted on it the prior 3 days, but then >> I noticed about .5 mm of side-to-side play on Friday. >> >> It had unknown mileage: this was the original BB-M730 (loose ball) in my >> '88 KOM. I'd cleaned and re-greased it just a couple weeks earlier when I >> had my frame re-finished. >> >> I really like the crank; it's 48-38-28 Biopace. It just feels right, and >> I ride so fast and easy on that bike. >> >> One issue: the original spindle is 124.5 mm. The closest replacement I >> could find was a 124 mm from VO. When I install it, the non-drive side >> will now be .5 mm closer to the frame, correct? I don't think it's worth >> worrying about. >> >> -Tim >> >> On Sat, Mar 14, 2015 at 2:17 PM, dougP <[email protected]> wrote: >> >>> Not a major project but one that was much easier done at home on my >>> schedule rather than a mid-tour breakdown. >>> >>> Bottom brackets are pretty easy to forget about, but it's easy to slip >>> the chain off the inner ring & turn them by hand. Spring is a good time, >>> and at-home is a good place. My thought for the day. >>> >>> dougP >>> >>> -- >>> >> -- > You received this message because you are subscribed to the Google Groups > "RBW Owners Bunch" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send email to [email protected]. > Visit this group at http://groups.google.com/group/rbw-owners-bunch. > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "RBW Owners Bunch" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/rbw-owners-bunch. For more options, visit https://groups.google.com/d/optout.
