Bigbus

I'm really tired of having to adjust my bottom bracket after every few 20 mile or less rides. I've replaced the bearings in it and have checked the lock nut to ensure it's not cross threaded and still the bracket comes loose. The crank shaft (square tapered) slowly moves from the drive side to the non-drive as I keep turning in the adjustment nut on the non-drive side. What will it take to replace the loose bearings with a sealed cartridge? I'm planning on pulling it apart again tomorrow and I'll have my caliper handy, but which dimensions do I need?
Thanks in advance and Merry Christmas everyone!

mtbikerinpa

Honestly it surprises me that an adjustable square axle bb is still in service. A cartridge replacement will boil down to what brand/family the arms are and what thread frame it is, and lastly what length spindle you have. Those aspects are fairly common to have on hand in a few options if you take it to a shop and ask what size you need. Good news is there are a lot of low-cost options to choose from that will give years of service.

Equally important to mention, TORQUE WRENCH always. An undertorqued square taper arm(all really but square particular) will be prone to wearing irreversibly and end up creaking. There are some variations on torque specs per manufacturer but I have not seen many below 40-45 ft/lbs.

Andrew R Stewart 

So the BB axle is somehow moving in the direction that the adjustable cup is preventing it in doing so? I'm confused by this possibility. Perhaps a second try at the description with different words will make things clearer.

But to try to answer your question- A few aspects of the replacement BB have to match the OEM one, a few others can vary.

The BB shell's threading and it's width are first. The vast majority of bikes made in the last 50 years have been ENG (British, 1.1370 x 24TPI) threading. Do know that there are still plenty of French and Itl. shelled bikes out there. Since we don't know what kind of bike you have (key data point missing) we can't assume here. As to the shell width that's easy to measure, in MMs. Most likely it will be 68mm (or 70 or 73mm).

The overall length of the BB axle is needed to be within the range that both established reasonable chain line and also insures that the chain rings clear the chain stays. Many loose ball axles are not symmetrical, meaning the dimension from the center of the frame/shell and the RH end is often longer then that of the LH side. But since the LH side has only crank arm/stay clearance concerns this side can vary. But to measure the RH side is important. Remove the RH crank arm and from the tapered end measure in to the shell's edge. To this add 1/2 the shell width (previously measured). Now you have what is 1/2 of a symmetrical axle. Since most all cartridge bearinged BBs are symmetrical double this RH side to get the total overall axle dimension.

If one knew that the OEM chain line wasn't best and one knew how much clearance existed between the inner ring(S) and the stay and one knew how much ft der range still existed one could change the RH arm's location. That's a lot of if one knews. This is why it can be best to have a motivated shop do this stuff. They will check out the before situation, dimensionally, and understand if any change is good and if so in which direction that change should be sought out. Having a selection of different BBs with slightly longer/shorter axles is nice to confirm what measurements and observations suggest. Andy

Bigbus

Wow! You guys are the best.Thank you for the input. It's a Huffy MTB frame with full suspension. I believe it's BSA threaded, 73mm and the axle length I will measure tomorrow when I have it pulled apart. I'm looking online at the Shimano UN-26 or UN-55. I replaced the bearings a year ago using bearings out of a Royce MTB that I was cannibalizing for parts. The Royce had an Asymmetrical setup, but the Huffy is symmetrical. Bearings were the same and in good condition.
To explain the axle shifting-when it comes loose, there is a lot of play on the drive side (wobble). As I tighten the adjustment nut on the non-drive side it pulls the axle toward it, essentially moving the front sprockets closer to the frame. Parts seem cheap and plentiful or I'd just replace the bike. Wife is constantly trying to get me to invest in a real bike, but with the sea air here I'm afraid it'll rust away before I ever truly enjoy it.

Bill Kapaun

Sheldon has a chart to determine what cartridge to use vs what spindle you have.
Look for markings such as 3-S etc.
https://www.sheldonbrown.com/bbsize.html

Did you happen to "overhaul" this and get bearing retainers backwards?

CycleryNorth81

Go with cartridge bottom bracket. You won't regret it.

Hoopdriver

I'm having a hard time visualizing what's happening. What is the "adjustment nut" on the NDS? Do you mean the adjustable cup? You describe screwing this in (clockwise) yet you say the spindle moves toward the NDS, which doesn't make any sense. Assuming that your cup and spindle BB is the correct one for your frame, is installed correctly, and all threading is intact, there is no reason for you having to adjust it every 20 miles. In any case, replacing it with a cartridge may be the best thing. Got pictures?

Really? A well maintained, quality cup and spindle BB will last pretty much for the life of a bike. I have a early 1980s Sugino cup and spindle BB on my all weather commuting bike that has needed nothing more than yearly maintenance. Still in perfect shape.

Andrew R Stewart 

Like Hoopdriver repeated, what you say isn't found in our many years of doing this stuff.

If when reassembling the crank/BB there's wobble (as in loose bearing adjustment) on the RH side it's also going to exist on the LH side. Whether you see it or not. If you don't have the LH arm attached then this might be hard to notice. Now if the RH arm isn't fully tightened you might be seeing the arm being loose on the axle???

Your saying that as you run in the adjustable cup the RH crank arm moves to the left is like saying that when you close a door the door frame (and attached wall) is moving to the door. (So they meet somewhere in the middle???)

Of course we're not there and we only are striving to understand what's going on. If you replace the BB with another chances are our need to understand will be moot. Andy

Bigbus

Let me try again. There is a large internal nut on the non-drive side with a larger outer nut (lock nut). When I loosen the outer nut and tighten the inner, it literally pulls the axle shaft from the drive side to the non-drive side before taking the play out of the axle. It's like my non-drive crank is moving away from the frame while the drive side moves closer-and it's almost put the smaller front gear (24 spd) up against the frame. Going out now to tear it down and get needed measurements. I hope that explains it. I've never had problems with any of my other bikes doing this and it started within 3 months of being new and it's now going on 3 years. TRS-740 model number. Other than that it's performed well for a Wally World special. All Shimano components. thanks

Andrew R Stewart 

A while ago Shimano did produce an adjustable version of their "cartridge BB" (and in quotes because the bearing design was an angular contact but the whole BB unit was installed as one piece) I forget the part numbers but Shimano also made an adjusting set of tools, these were basically two thin wall sockets with one residing within the other. What I also don't recall is the right side bearing orientation. It might be that the "cup" was reversed, inboard to the cone. This would result in the axle moving to the LH side as bearing adjustment was taken up. This is a very uncommon configuration. Only the even older Shimano Front Freewheeling System (of the late 1970s/early 1980s) used a similar design, as I remember.

No doubt we are all confused. I suspect most here have never seen this (if that's what you actually have), I forgot about this BB design as it's been a few years since I saw one and a few years before that since the second to last exposure. This is a case where a photo would help our understanding. I'll pay attention to this thread for the real facts as you discover them. Andy

Ferrouscious 

Yes, pictures would help massively.

mtbikerinpa

Basing on your updated attempt to explain, what you are saying is that the lock ring is changing your adjusted setting when you go to tighten it? That is pretty common on cheaper end bikes due to slop in the threading. When the nut is tightened it can pull or push on the inner portion sometimes in a sizable way that just takes a lot of fiddling to compensate for.

The surprise remark was regarding the concept that non-sealed non-cartridge units are still being produced, not that they are still rolling. As for longevity an open-ball non-cartridge will last a very very long time if you do enough maintenance to it and keep it adjusted properly. For the rest of us who don't want to bother, there is cartridge which lasts long enough without the hassle.

Bigbus

Okay, let me try again. What I referred to as adjusting nut is really the non-drive side bearing cup. So I pulled it all apart and the bearings on the drive side came out with the grease and the bearing cradle was mangled. The non-drive side bearings looked really good so I dug through all my bike junk and came up with another bearing assembly that fits and cleaned everything up, repacked, put the bearings in the cups with the race side facing toward ctr of frame and put it all back together. After adjusting the slop out and locking the nut down tight, I had to readjust the front derailleur because now the sprockets are back out where they should be in relation to the frame. I'm not feeling confident with my fix and know I am just postponing the inevitable so I'm going to get me a sealed cartridge for it since I like the rest of the bike. Maybe it's just all the miles I've put on it, but I like it, even more since the dear wife painted the frame for me last summer so it doesn't say Huffy anymore. It is a Giant designed frame. So 68mm x 120mm with British threads and square tapers here I come. Thanks to all the gave me input,

Bigbus

One last question. After doing some looking online I have come up with 117.5mm and 122mm on the cartridges. Mine measures 120mm. Can I go with either of the others and if so, which is better, the longer or the shorter? Thanks again for everyone's input.

mtbikerinpa

You will need to have enough length to keep the crankarms from hitting the frame but also a chainline offset built in to keep the chainrings where they need to be. Those two measures interact with eachother and can take some fiddling unless you take to a shop to measure/cross refference.

Andrew R Stewart 

And don't forget about the ft der's available range (if the limit screw was to be played with) to the inside. I have had to pull a replacement BB because with the new ring placement (closer to the frame) the ft der would run out of movement or hit the seat tube before down shifting happened. Andy

andrewclaus

It sounds like, as surmised above, the bearing retainer was installed backwards years ago and you've been fighting it since. The races on the spindle and/or cup may be damaged now, as well.

Good points above about a new BB changing the chain line. It often takes more than one try.

Also pay attention to the post about tightening the locknut changing the bearing adjustment due to sloppy threads.

If you have access to a co-op, there may be a bin full of salvaged spindles and cups to replace the original stuff (and a mechanic to check your work).

Bigbus

Thanks for the good tips. I will check my clearances and then go from there. I did replace the non-drive cup even though that had the better bearing still in it, but I couldn't find another for the drive side, which is CCW threads and the cup looked a little worse for wear. Like I said earlier, I don't have much faith in this fix and it's only buying me time so I can keep riding until I can do a more permanent fix. I've moved around a lot in my career and with each move I was always giving my bikes away to non-riders, hoping to instill a love for riding like I have. What I would give now to have a couple of those babies back LOL. Thanks again for everyone's help.

dedhed

Is your existing spindle symmetrical?

https://www.sheldonbrown.com/bbsize.html

https://www.sheldonbrown.com/chainline.html

Bigbus

[QUOTE=dedhed;20720032]Is your existing spindle symmetrical?


NO. It's 4mm offset. Is that going to be a problem with a bottom cartridge?

New Edit here: I followed the link you provided and it appears that I have a '3N' spindle so I'm thinking I need a 124mm symetrical cartridge. I've located a 122mm and am pretty certain I can make it work. Thanks for the heads up.

fietsbob

Measure the drive side , match that , to keep the crank set in similar place as you had on the bike first other side can be longer ..

Since you will only need a removal tool once, to take off the original fixed cup, assemble a Sheldon B's BB cup remover in the hardware store..

https://www.sheldonbrown.com/tooltips/bbcups.html



A Shimano UN26* style cartridge BB needs a different tool to install it.. *( there are even cheaper than the under $20 Shimano made ones to be found)







....

Bigbus

I've removed both bearing cups with no problems so I;m assuming I don't have a fixed cup on this bike. No snap rings or anything like that. They just screw in from either side with opposite thread rotation. The drive side snugs down and leaves the non-drive side for bearing adjustment and lock ring. And believe it or not, I have the tool for a UN-26 BB. It came with a bunch of other bike related tools I've been collecting over the years. Thanks

Bill Kapaun

The fixed cup is called "fixed" because it's non adjustable. Not because it's a permanent fixture.

Bigbus

Thanks for clarifying that Bill.

Bigbus

I do like the ingenuity behind the home made tool, but I use a 1 3/8" open end wrench. Hold it in place with one hand and tap it with a rubber mallet and it comes loose easily.