sirclicksalot

So I've really tried to do my Google due diligence, as well as Sheldon Brown pilgrimage, but I'm stumped. Here's my question:

I've got this: Shimano N600 on a 1985 Trek 620. Started ticking on the ride home yesterday, and sure enough, there's wiggle in the BB. As I'm not committed to keeping it period, I immediately thought it might be good to replce the BB with a cartridge. I've measured my chainline, and it's the Shimano standard for a triple, 45mm. What I can't figure out is this; what spindle width do I want if I am going to switch to a cartridge BB? I know the current spindle length is 121 from the Velobase listing, but the only 68x121 JIS BB I can find is this one, which is a bit steep. Plus, it seems like from what I've read that cup&cone spindle lenght doesn't correspond 1-to-1 with cartridge length (I'm mostly thinking of what was done here, which is a different crankset, but same BB shell and a full 11mm shorter, granted with a 1.5mm spacer)

I'm sure there is some kind of standard conversion for figuring this out, but I'm stumped. Any help is greatly appreciated.

ThermionicScott 

Steep and unavailable. For that price, you could buy a 118mm and 122.5mm Shimano UN55, use the one that lines up better, and still have money left over.

RubeRad

Or spend like $1 more and get UN55 with a metal non-drive-side cup.

I don't think you need to match the 121 exactly, and it seems to me square taper spindle lengths would be 1-1 comparable (as long as you compare JIS-to-JIS or ISO-to-ISO). How much clearance do you have right now from granny to chainstay? If you have 5mm clearance, then I'd guess a 118 should be safe. Or moving everything 1-2mm outboard can't make that much difference. Last time I checked, millimeters are small.

This brings up a related question though (if I may hijack your thread); I am going to switch out a square-taper double crankset for an octalink double, thus I need to replace the BB as well. Are the spindle lengths comparable there? I.e. can I measure the sq. taper BB spindle, buy a same-length octalink BB, and end up with the same chainline/clearance?

bradtx

sirclicksalot, The Shimano cartridge BBs I've used were all symmetrical. If you have an asymmetrical crank set the chances are very good you'll need a slightly longer BB spindle, unless there is ample clearance for the chain rings.

Brad

sirclicksalot

So should I assume that style of BB would be asymmetrical? I realize I should just take the damn thing apart and look at/measure it, but I'm trying to do all my research first before diving in, as A) it's a new bike (to me), and B) I'll probably have to do it at a community bike shop, as I have no stand/lockring spanner/crank extractor (oddly enough, I do have a SPA-1, but damned if I can remember why). So I'd like to have an idea of what I'm getting into and what parts to get before I dive in.

So if it's asymmetrical, is there any way to measure to determine how much to add to the overall length, without pulling the cranks?

sirclicksalot

That was exactly the part I was looking at for a replacement. I guess $25 to give it a shot isn't a big deal, but as I replied to bradtx below, I'm trying to do my homework first. I'm also surprised how little info I've been able to find online, I spent probably 2 hours researching this last night, and found some stuff, like Messr Brown's partial BB size guide, but it seems to stop at 1990 for Shimano stuff.

davidad

https://www.biketoolsetc.com/index.cg...r-Spindle&q=&s=

RubeRad

https://www.ebay.com/sch/i.html?_saca...o+un55&_sop=15

sirclicksalot

So is what you are saying that something there that's close (122 or 119 with spacers?) will work?

Ummm, thanks, I guess? I wasn't really having trouble finding un55's, but Ebay ispretty cool. However, after searching ebay for 68x121, I found the white industries BB again, but it had in the description the following: . So again, is the number I'm looking for 121 or 113? Or something else?

davidad

If your axle measures 121mm that would be the ideal size. The 122 will work. The size would be 68X122. The 68mm is the width of an English road bottom bracket.

RubeRad

If you're at 121, the safest bet is 122 or 122.5. If you have a lot of clearance (like 5mm or more), then you should be able to safely drop to a 118.

(That White industries 121 vs 113 is probably a typo. If you want White, you should be able to ask the seller a question and get them to clear it up).

My LBS (blackmountaincycles.com) has a passthrough search for the QBP catalog, with prices, looks like $29.99 for any size UN55. 68mm is the most common, maybe there is a LBS near you where you could just bring your bike in and try out a few sizes if they have 118 and 122 or 122.5 in stock? If you are buying a part, maybe they would give you a break on installation, or let you borrow their tools?

Of course, you're in Portland, so there's co-ops on every other corner, right? UN54/55 seems like something even a co-op would stock, for all those vintage square-taper BB out there. Then you could buy for a good price and probably use co-op tools for free.

Yet another option, there's a good chance you don't need a whole new BB, just repack with fresh bearings. The bearings are close to free, so instead of buying a bottom bracket, you could buy bottom bracket wrench(es). Or improvise with the SB fixed-cup tool which is just a 5/8 bolt&nut and some washers. For the adjustable side, theres somebody at BF that made an awesome wrench by filing the jaws of ordinary widemouth pliers (channel lock?) so the tip of the jaws had teeth to fit into the notches. You can also get away with tapping in the notches with a hammer and flathead screwdriver (but you'll likely scratch or gouge it). And actually if the bearings are the only issue, "For normal servicing, only the adjustable (left) cup need be removed. It is a bad idea to remove the fixed (right) cup for a routine cleaning and repacking."

All that is if the bearings are the only issue, not the races or the cups. Opening it up should help you decide. Of course, if all that is too much hassle for you, then cartridge is the way to go.

Grand Bois

Don't be confused by the article you liked to. He changed cranks, that's why he needed a different length spindle, not because he went from a cup and cone to a cartridge bottom bracket.

sirclicksalot

Thanks to everyone for the info. Looks like I'm off to the LBCoop to do some tinkering.

sirclicksalot

Thanks, I kept seeing enough different mm #'s side by side that I was wondering if I was missing something where spindle lengths needed to be converted/offset somehow.

CACycling

The BB spindle is determined by the crankset, not the frame. You need to get the length specified for the crankset you choose.

To the OP, I'd just clean and grease the cup and cone unless it has issues.

Grand Bois

I agree that you should keep the original BB if possible. I'm not one of those that considers a cartridge BB to be an upgrade. I use them only when I have to, like when I couldn't find a long spindle for thick cups when I converted my PX10 to a Campy triple.

JiveTurkey

I'd measure the spindle myself. The crank arms would need removing, but the spindle can be measured with calipers while the BB is installed.

From the pictures on VeloBase, it appears the spindle is longer on the driveside than non-driveside. If your current spindle is 121 mm and offset like the one on that page, you'll need a longer symmetrical spindle for cartridge, if you want to preserve the chainline.

According to this chart, a 121.5 mm asymmetrical BB is replaced with a 127 mm cartridge. This would preserve the chainline, but bring the non-drive-side crank out a few millimeters. I'd look for a cartridge BB in the 126-128 range, like this one in 127.5.

bradtx

sirclicksalot, Look at this info: https://sheldonbrown.com/bbsize.html .

Brad

sirclicksalot

Yeah, I checked that out, but unless I'm missing some odd part designation (like the fact that velobase says the part name is 600EX, but Trek calls it the N600, and VB also says it was part of the Deore Deerhead group), I don't think it's included in that list. In fact, as there's nothing Shimano there that's older than 1990, I'm pretty sure it's not included.

Although, I just went and looked at it again, and I guess the "Japanese Bottom Bracket Spindles, Traditional Cup And Cone Type" section is possibly going to be helpful once I take it apart and check the spindle. It's looking more and more that repacking/servicing is the way to go.

sirclicksalot

Man, I was just thinking from re-reading this post alone, I think sheldonbrown.com could be the worst-looking website with the best Google pagerank ever.

Backlinks? Oh yeah, we got a few.

Bill Kapaun

The "Deerhead" group was for mountain bikes. My 86 Rockhopper had that group.
IIRC when I switched to a cartridge, I used a 127mm and it worked out OK.

The trouble with spindles is that some have an offset & some don't.
I've ran into some old TREK Fleetstreaks where one was a triple and the other a double (I have know way of knowing if they actually came in both flavors).


They used the same spindle, but used the "long side" for the triple and the short side for the double.

RubeRad

Good point. Somebody should scrape all that fantastic content and reorganize it as a free smartphone app. Or maybe 99c; is there some kind of SB memorial fund out there or something? If not, I'm sure there's some kind of bicycle-related charity that would be appropriate.

sirclicksalot

Just an update: got the tools, took it all apart (1st BB for me!), cleaned & regreased (some very minor pitting on the spindle cone on one side, but not bad), and after some cursing, and one thrashed lockring, got it dialed & smooth on the vinyl like Lionel Richie.

Much thanks to everyone here for the advice.

Road Fan

For future reference, to match chainlines you need to match BBs for how long the drive-side stub is. In the old Sutherland's manuals (4th, 5th and 6th editions are worth seeking out if you're going to do a lot of this) this is called Shell to End Right (SER), and it is the distance from the end of the BB shell to the end of the spindle for an installed BB, cartridge-type or spindle-type. This number plus the shell width, 68 mm in your case, minus the overall spindle length, gives the equivalent dimension for the left or non-drive end.

If you match the tapers and the SER, assuming the spindle was installed with its intended cups, the chainline with spindle-type should match the chainline with cartridge-type. And if the overall lengths match, the positions of the non-drive crank arms should also match.

sirclicksalot

That is some good info, much thanks. So the 7th edition manuals don't include this info?