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loose bearing BB to cartridge

Old 05-30-16, 04:16 PM
  #1  
specialgreen
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loose bearing BB to cartridge

I bought a used '91 trek 7k with Deore DX, the last year they used ball, cup&race bottom bracket. The chainrings need replacement, and the BB has some decent play in it (enough to make the chain rub the front derailleur on the left foot stroke). I cleaned and repacked it (temporarily reused the caged bearings), but couldn't tighten it enough to get rid of the loose play in the axle. Is that something which might be overcome using 10 or 11 loose ball bearings, intstead of the 9 caged ball bearings? There is some pitting on the axle races, but not too bad, and the cups are smooth.

I suspect that the axle is worn out, in which case I'd probably replace with a catridge, when I replace the crankset. BB shell is 68mm; the crank axle measures 133mm end-to-end. Crank appears to protrude 4 mm farther on the chainring side. This seems to match a discussion from rec.bicycle.tech
Help: Replace 68,133 botom Bracket - Google Groups

I'm guessing I could get a 68x130 Shimano tapered-square, which would be put the chainrings 5mm inboard. I could use a triple crank with the inner chainring removed to gain-back about 4mm. I'd prefer Octalink, but don't see many long options. Does "120mm" mean the same chainpath whether you'r eusing tapered-square vs Octalink?

Last edited by specialgreen; 05-30-16 at 05:06 PM.
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Old 05-30-16, 04:45 PM
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Cartridge Shimano UN 55 are not that much Money though they top out at 127.5, longer than that Phil Wood is a maker of long axle BB's

Made in USA prices Though..


I'd prefer Octalink,
Good luck it has been made in the past , you need the BB and the crankset , and will have to find it on EBay.

Last edited by fietsbob; 05-31-16 at 12:23 PM.
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Old 05-30-16, 04:48 PM
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The longest square taper cartridge bottom bracket by Shimano is, IIRC, 127.5 mm so you will have to try one of those and see if it works. I once had an SKF bottom bracket that was 130 mm but it was a real odd-ball and i don't know where to find one these days. Phil Wood sells square taper bottom brackets with up to 155 mm spindles but it's cost would far exceed the value of the entire bike. A complete new crank and compatible bottom bracket is the better way to go.

As to the current BB, it seems like all it needs is correct adjustment and the bearing ball count shouldn't matter. If it worked originally with 9 caged balls it should still work with 9 caged balls. Axles don't "wear out". They sometimes develop bad pitting which requires their replacement but the races don't get smaller in diameter.
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Old 05-30-16, 05:52 PM
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If you know how to measure spindles and can do math it's not hard to get a good approximation of a current BB replacement size. One key is to find the old spindle's center between it's bearing surfaces and only measure from that to the drive side spindle end. The new spindle length is twice this. But there's some fudge depending on a few factors so the best replacement size will be determined by actual trial.

Changing the number of loose balls won't change the pitted condition of the spindle or cups, won't change the spindle size needs of the ability to get a best adjustment. Andy.
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Old 05-30-16, 06:19 PM
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Originally Posted by HillRider View Post
The longest square taper cartridge bottom bracket by Shimano is, IIRC, 127.5 mm
I see a few options in an eBay search with "bottom bracket 68 130".

If that doesn't work, looking at my existing setup, the axle is asymmetrical, 4mm longer on the chainring side, so if I imagined it to be symmetrical by adding 4mm to the non-chainring side, it would be 137mm wide. If I just put a 130mm BB on, that would move the chainrings inboard 3.5mm, which might work, but maybe not.

Ifx not, an option would be to adjust the low-stop to just avoid using the granny gear (I never use it anyway); or optionally just remove it altogether. The index on my 3x7 triple crankset appears to be 9.296mm, so removing the granny gear would move the chain-line outwards 5.8mm (about 2/3 of an index), versus the old granny+middle ring chainline. That may be enough clearance to allow for the larger middle ring (now the low gear).
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Old 05-30-16, 06:27 PM
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If yours is the 3TR spindle, you may be in luck. Sheldon's database says that that measured 42mm left of the center section, and 39mm right of it. So when mounted in a 68mm bottom bracket shell, you'd get a length of about 31mm from the shell to the end of the spindle on the right side. A 127mm UN54/55 will have 30mm from the BB shell to the right end of the spindle, and about the same on the left. As long as your old BB didn't place the NDS crank really close to the chainstays, I'd be optimistic that a 127mm sealed BB would do the job just fine.

If nothing else, you could start with a UN26, which you can get for $10-15 shipped, so you wouldn't be out much if it doesn't work.
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Old 05-30-16, 06:29 PM
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You said you purchased the bike used. Are you certain the current bottom bracket is the correct size? When I searched for Shimano Deore DX bottom brackets, it appears it was only made in a 122.5 or 127.5. It would help to know the chainline measured from the centerline of the seat tube to the middle ring.
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Old 05-31-16, 11:59 AM
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Good thought on the BB, sensei. Chain line looks like 49.5mm. It doesn't look to me like there is excessive room for the chainrings or crank arms.
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Old 05-31-16, 12:15 PM
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Originally Posted by specialgreen View Post
...I'd probably replace with a catridge, when I replace the crankset.
As the spindle length is mostly determined by crankset not the frame, choose your new crankset and get the appropriate length BB for it.
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Old 05-31-16, 12:28 PM
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Originally Posted by CACycling View Post
As the spindle length is mostly determined by crankset not the frame, choose your new crankset and get the appropriate length BB for it.
+1
IF you are going to change the crank, you'll most likely need a much shorter BB then what they used 25 years ago.

The spindle should have a "code" on it such as 3S, 3P etc.
that can help you determine the "symmetrical equivalent" of a cartridge BB.

Sheldon Brown's Bottom Bracket Size Database
Scroll down just a bit-
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Old 05-31-16, 01:05 PM
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Originally Posted by CACycling View Post
As the spindle length is mostly determined by crankset not the frame, choose your new crankset and get the appropriate length BB for it.
This was my thought. If you're planning on replacing the crankset, why do you care what bb spindle length is on there now?
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Old 05-31-16, 02:14 PM
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specialgreen, Make sure that the chain rings are replaceable. Some are riveted on, if so you'll need a new crank set.

Brad
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Old 06-01-16, 09:57 PM
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Originally Posted by Bill Kapaun View Post
+1
IF you are going to change the crank, you'll most likely need a much shorter BB then what they used 25 years ago.

The spindle should have a "code" on it such as 3S, 3P etc.
that can help you determine the "symmetrical equivalent" of a cartridge BB.

Sheldon Brown's Bottom Bracket Size Database
Scroll down just a bit-
I'm not sure how to read Sheldon's page: it describes the chainline for each Shimano crankset, but doesn't mention which BB width was used in the measurement. I may be confused, but it seems like the chainline will be: half the width of the BB, minus whatever width is removed by the inward curve of the crankset. So I'd expect to read two separate numbers: the BB width (e.g. "68x126," which adds 63mm to chainline), and the offset of the particular crankset (e.g. "Shimano Supositorio MTB Triple has -14 mm offset to middle chainring"), and the combo would have 63 - 14 = 49 mm chainline.
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Old 06-01-16, 10:11 PM
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Originally Posted by specialgreen View Post
I'm not sure how to read Sheldon's page: it describes the chainline for each Shimano crankset, but doesn't mention which BB width was used in the measurement. I may be confused, but it seems like the chainline will be: half the width of the BB, minus whatever width is removed by the inward curve of the crankset. So I'd expect to read two separate numbers: the BB width (e.g. "68x126," which adds 63mm to chainline), and the offset of the particular crankset (e.g. "Shimano Supositorio MTB Triple has -14 mm offset to middle chainring"), and the combo would have 63 - 14 = 49 mm chainline.
Look at the "spindle chart" to read the "Code" to determine the length of what you have now.
Then you know where you need to go.
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