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Upgrading to a cartridge BB
#1
Hey folks! First post. I'm working on a salvage project, re-building a road bike from an old frame. I want to put a cartridge BB in it, but I need some help figuring out sizing, etc. Disclaimer: I'm terrible with brands, but good with the mechanical side of things; you may have to hold my hand a little through this one.

I've looked at some of the stuff from Sheldon Brown, but it's really going over my head. Or maybe my mind is just saturated... I've been doing a lot of reading...

Anyway, the old spindle was a 3T, which I believe means I'd be best suited picking up a 130mm symmetrical unit. My problem is that I don't know:

1. Do I need to be worried about JIS vs. ISO tapering?

2. What style(s) of BB cartridge should (or could) I use?

3. The old crankset was a 2-ring set. I want to upgrade to three. What do I have to consider in terms of cartridge sizing to make this do-able?

Thanks for any help you can provide. I'm happy to provide more info if need be Smile

--Syntax
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#2
Hi SS! Welcome to BT!
What old bike are you refurbing? That might dial in some responses.

Re-read q #3. Often, the mfr of a crankset will suggest the approx axle length for that model. It's up to you to determine the BB Shell width (68 or 73mm are common).

As you've already discovered Mr Brown, you're a step ahead of the game! Most of us have that sitemap memorized and can probably help explain certain things if you point us to a page.
Wheelies don't pop themselves. (from a QBP fortune cookie)
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#3
(11-10-2013, 12:07 AM)RobAR Wrote:  Often, the mfr of a crankset will suggest the approx axle length for that model. It's up to you to determine the BB Shell width (68 or 73mm are common).

Oh my god. This. So much helpful Smile Thanks! I think this is the big piece I was missing!

I'm actually unsure of the brand of the frame. That said, the BB shell is ~69-70mm. I take it that's just a bad ruler? I would think it to be just a standard 68... everything else on the bike up to this point (seat tube, head tube, fork spacing) has been "standard."
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#4
If you're getting 69 or 70 on a ruler - my bet would be it's a 68mm with paint on the mating surface and you have a good eye. It's best to measure with a dial caliper, though. Is the 130 mm that you're reading based in true axle length at end of taper and not including any threaded part that often exists on spindles that use nuts rather than bolts?
On your question of JIS vs ISO - since Shimano is the big dog in the game these days, almost every tapered spindle follows thier lead.
Can you give an approx age of the frame? I ask because my idea of 'old' may differ from yours. Smile

Now, I'm gonna rain on your parade but, only in the interest of saving you $$. What you are attempting to do (dbl to triple) can be tricky. You have to watch the chain-line or you will have shifting issues. Don't expect to be able to just swap a 68 x 130 BB for another if you're gaining a chainring. You might run into the issue of the Triple sets little ring rubbing on the frame, or your front drlr may not have enough travel to spread over 3. See?
Wheelies don't pop themselves. (from a QBP fortune cookie)
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#5
(11-10-2013, 01:43 AM)RobAR Wrote:  It's best to measure with a dial caliper, though.
Yup. I'm going to use one to confirm before I make any purchases.

(11-10-2013, 01:43 AM)RobAR Wrote:  Is the 130 mm that you're reading based in true axle length at end of taper and not including any threaded part that often exists on spindles that use nuts rather than bolts?
I found the 130mm suggestion on SheldonBrown. Ctrl+F (or Cmd+F) "3T"

The old spindle is more like 126/127mm w/o the threaded bosses. Which is odd, because the 3T is described there as being 123mm...

(11-10-2013, 01:43 AM)RobAR Wrote:  Can you give an approx age of the frame? I ask because my idea of 'old' may differ from yours.
Hard to say. '85ish, maybe? That said, Sheldon Brown has noted regarding front derailer cable pull that:

Some older designs use a loop of cable housing running from a stop near the bottom of the down tube. This design hasn't been used since the mid-1970s.

My frame has such a stop. I really don't think it's that old, though. Makes me think it's a cheapie... (which is fine with me; this is just a pet project)

(11-10-2013, 01:43 AM)RobAR Wrote:  What you are attempting to do (dbl to triple) can be tricky. You have to watch the chain-line or you will have shifting issues. Don't expect to be able to just swap a 68 x 130 BB for another if you're gaining a chainring. You might run into the issue of the Triple sets little ring rubbing on the frame, or your front drlr may not have enough travel to spread over 3. See?
Ok. To be clear, the entire drive train is getting replaced. So, I figured that getting a new BB properly suited to the new triple crankset (as per mfr instructions) would help avoid such problems... No? Same for the rear derailer: I had planned to buy a new one based on the new chain ring size.

Truth be told, I always had mountain bikes (even though I rarely took them off road), so I'm just used to triple rings. Do you think I should just go for a double? I never cared for much other than the top two rings, anyway...
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#6
Double to triple = new front derailleur, and most likely new shifter for said front derailleur.

Agree that matching the crankset and BB is best. For the flatlands of Silicon Valley; I like 50/34 crank set with a 11-23 or 12-25 8 speed cassette (9 speed and higher chains are narrower and not as strong) and 622 or 630 rims (700c or 27").
Nigel
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#7
(11-10-2013, 08:55 PM)nfmisso Wrote:  Double to triple = new front derailleur, and most likely new shifter for said front derailleur.

Agree that matching the crankset and BB is best. For the flatlands of Silicon Valley; I like 50/34 crank set with a 11-23 or 12-25 8 speed cassette (9 speed and higher chains are narrower and not as strong) and 622 or 630 rims (700c or 27").

Definitely. Yes. New front drlr and shifters too. Forgot to mention. Thanks for the advice re: flat roads Smile Sounds like I'm on the right track!
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#8
2 Questions:

1. Is there a karma system on this website? You've both been very helpful already but I don't see a way to +1 or thumbs up or rate or mark-as-solved or whatever.

2. I'll post this as a new thread, too, but I figured I'd ask here just in case. I'm looking at the Shimano Tourney A070 double crank set. Can you help me make sense of the spec sheet I've found for a compatible BB? Shimano's recommendation is the BB-UN26, for which there at least 5 different lengths, from what I can tell.

In the "Axle length / BB spec" section, there are 8 categories, all applicable to 68mm (BC1.37) or 70mm(M36) shells:

HOLLOWTECH II construction
109.5 mm
118.5 mm
113 mm
121mm
MM107
MM110
LL113

"MM110" looks to be the one applicable to me (LL113 if I were going for the A073 triple). What are those? What do they mean? Does this tell me what the actual length of the darn thing needs to be?
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#9
From Amazon: http://www.amazon.com/Shimano-FC-A070-Road-Crankset-Cog/dp/B007Q4P490


"Type FC-A070 w/ CG Length / Teeth 170x50-34 Spindle Type 110 SQR JIS Color BLK Bolt Pattern 110x5B Weight Speed 2x7"

It says 110mm square JIS taper.

If you want to go with Shimano, go with a UN55 68x110 : http://www.amazon.com/Shimano-Square-Taper-Bottom-Bracket/dp/B0068FVOEM/ref=pd_sim_sbs_sg_7

If you go with a Shimano BB, you will also have to purchase the bolts to hold the cranks to the BB, some other brands include the bolts.

My SR has a Shimano A050 with a Vuelta BB (which included the bolts).
Nigel
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#10
(11-11-2013, 03:15 PM)nfmisso Wrote:  It says 110mm square JIS taper.

If you want to go with Shimano, go with a UN55 68x110

If you go with a Shimano BB, you will also have to purchase the bolts to hold the cranks to the BB, some other brands include the bolts.

Awesome. Thank you so much for confirming my suspicion on that.

Any insight on why a 110mm BB is categorized as MM110 (and, similarly, why a 113mm is categorized as LL113)? This is especially perplexing considering the otherwise intuitive convention for 109.5, 118.5, and 121 mm sizes.

And what's the difference between 113mm and LL113, anyway?

I don't have my heart set on anything yet in terms of a BB. Just wanted to know the size I need for the crankset. Thanks for the recommendation of the UN55.

And not to worry about the bolts; I've got buttloads of 'em!
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#11
I'll probably get hammered for this, but this is how I do it, as I often find the suggested BB size for a given crank set to be incorrect for my application.
Test fit the new crank set on the old BB. Check fit/chainline & measure. Although not perfect you can see if a 110mm is going seem way off after the test fit.
I prefer Tange sealed BBs. They are built like a brick crap house compared to the Shimano. The fit of the body into the adjustment cup is much tighter and it is of steel rather than aluminum construction.
Purchase the proper bolts for the cranks, they are usually cheap, application specific, with locking flanges etc...
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#12
Like Jef; I use the recommended BB as a starting point; I find that low to mid end Shimano tends to bias the chainrings outwards, => use shorter than recommended by Shimano. But that is a generalization that does not always apply.
Nigel
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#13
I've even pulled BBs from another bike to test fit, even if it's not the proper size you can do the math & extrapolate.
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