Square-Taper BB 68 (1.37 24T) Crank-Arm Fixing Nuts (not bolts) Comes Loose

[EdSr]

New to forum, just signed-up, after reading an entry about constantly loosening crank-arm fixing BOLTS.

In my case, my original BB, uses crank-arm fixing NUTS (original equipment, not jury-rigged), instead of BOLTS. I’m “dating” myself, but I’ve had this bike since new.

I’m constantly re-tightening the nuts, every other ride, or worse, at times after a long ride. I have had difficulty finding newer nuts, to see if this resolves the problem, so have been using Loctite Blue Threadlocker, which have given me a few days to a week, before having to re-do the process. The threads on the nuts, appear to be fine, no damaged or stretched thread tracks.

Just the other day, found my lighted magnifying glass, so while I had the crank-arm off, took a good look at the male-threaded end of the crank-arm spindle. Sure enough, I can see very small nicks missing in some of the thread tracks. I can barely seem them, so there is some doubt, that this is the problem (but SMALL doubt).

Some background…
I’ve had this 1985 Schwinn Traveler since… 1985, NEW, original owner! Never had to do extensive maintenance… heck, never have done any extensive maintenance! Never needed to… till now! It has lived a sheltered life (not figuratively), but have ridden it hard (Catskill Mountains), the first two years, then my company (I’ve Been Moved) moved me out to Illinois, plus hectic schedule, ended my touring/cycling… for years!

Now in Florida, over the last 2 years… back on the road again! Even scarier? Everything I didn’t do when I first got my bike in 1985… I’m teaching myself (I’m assuming properly) to do… armed with two books… Park Tools BBB of BR 4th Ed and Zinn Road Bike Maintenance…

Acquired the time, patience and tools… working on the confidence part right now. In “middle” of confidence building, have convinced myself to take on a project, to build my skills… set a budget, while trying to keep this bike on the road.

The project? Upgrading this original double crank 6 speed, to a double crank 11 speed, without ANY downtime (other than installation time). I could have just waited till I had ALL THE PARTS, then just hit it all at once! But no! I had to do it the hard way! Sucks to be me!

As most of you may know… there are components that can be repaired or replaced, do it right the first time, job over and done with, till ya wear it out! Then there are components (due to specs or requirements) that it’s a one thing leads to another, chain reaction! Replace this, gotta replace that… and so and so on!

Well, due to circumstances that time and or failure has allotted, I’m right at the point of “final” project linchpin. That is… the drivetrain…. And I’m not ready to do the drivetrain YET! But the BB/Crank-Arm issue, is forcing me to change the BB!

I know I’ll need to eventually change the BB, but it won’t be the same BB. So I decided to buy another new one, to buy me more time, till I’m ready for the heaviest part of the overall project… but now, getting the CORRECT BB?

The spindle has male threaded ends… hence, crank-arm fixing NUTS! I’ve currently measured, total length of spindle, end-to-end at 150.55mm, asymmetrical (which is common). Current BB installed, is a Sugino 68/? 1.37 24T (which I haven’t removed from the shell yet! (Chicken? Probably!)

So doing my Google Research, got me AND you (if you’re currently reading this, throughout this “story”) where we meet! So if you followed me to this point, I need to repair, or preferably replace the BB, with a sealed BB, so that I can gain back reliability and trust without packing extra tools or “breaking down” while on the road! But I’m NOT finding any sealed BB’s with male threaded-ends, which then it’s critical to get the measurement correct, on the one installed!

Anyone want to take a whack at this one!? Appreciate the insight!
Otherwise, it’s crankset, BB, Front & Rear Mech, Chain, Brifters, Cassette, Re-Lace Rear Wheel/Hub, Widen Rear Drop-out, Pedal components… one thing leads to another, before I’m back on the road!

Not ready for that point!

[Jesper]

(05-04-2021, 06:37 PM)EdSr Wrote:  [align=left]New to forum, just signed-up, after reading an entry about constantly loosening crank-arm fixing BOLTS.

In my case, my original BB, uses crank-arm fixing NUTS (original equipment, not jury-rigged), instead of BOLTS. I’m “dating” myself, but I’ve had this bike since new.

I’m constantly re-tightening the nuts, every other ride, or worse, at times after a long ride. I have had difficulty finding newer nuts, to see if this resolves the problem, so have been using Loctite Blue Threadlocker, which have given me a few days to a week, before having to re-do the process. The threads on the nuts, appear to be fine, no damaged or stretched thread tracks.

Just the other day, found my lighted magnifying glass, so while I had the crank-arm off, took a good look at the male-threaded end of the crank-arm spindle. Sure enough, I can see very small nicks missing in some of the thread tracks. I can barely seem them, so there is some doubt, that this is the problem (but SMALL doubt).

Anyone want to take a whack at this one!? Appreciate the insight!
Otherwise, it’s crankset, BB, Front & Rear Mech, Chain, Brifters, Cassette, Re-Lace Rear Wheel/Hub, Widen Rear Drop-out, Pedal components… one thing leads to another, before I’m back on the road!

Hello Ed,
Welcome! Sounds like a complete rebuild is in the making. I don't know what to make of your loose crank arm nut/spindle problem. I don't think I have any BBs with the nutted vice bolted on cranks. Are the cranks tight without play when fitted (I assume aluminum cranks)? If the cranks don't fit properly due to wear from being ridden while loose you may need to replace the cranks themselves. I would replace the nuts first (if cranks are good with properly spec'd nuts), or try adding star lock washers (thinner than split lock washers) if you have ample threads to do so. Your actual BB spindle length should not include the male threaded portion of the spindle when determining length. The 68 refers to the BB shell width (68mm), the 1.37"× 24 TPI is the cup and shell threading. If you increase to an 11 speed rear cluster (cassette) you will need to "cold set"/bend the rear fork to accept the wider hub. I am not a big fan of doing that; if I put a wider rear hub on an older bike I'll keep it to within one size larger or where I only need to manually spring apart the fork a little when mounting the new wheel. If you are going the route you outlined, I would have a properly outfitted shop do the work so the frame alignment can be maintained. You would also have to "re-dish" the rear wheel with an 11 speed rear. You would also be affecting the chainline so another issue may arise where the BB spindle offset and total length might need to be different in order to achieve the desired chainline. I would recommend a sealed bearing BB assy. with bolts as opposed to nuts, either way you need to make sure that the taper length portion is the same for the cranks (there is a difference, e.g. JIS long and short, and ISO). A good online source (there are many, check this website here also) is Sheldon Brown's site which details many of the issues you would be facing. You could probably fit a 7 or even an 8 speed without going through too much hassle (no cold setting of frame). I also live in Florida most of the year and even being in my late 50's I don't find the need for 8 speed and larger cassettes due to the flat terrain. Most 9-12 speed cassettes have only one tooth difference between the first 3-5 (or more) smallest cogs; thus, you can easily do away with 2 or more cogs ( use a 7 speed vice a 9 speed, or an 8 speed vice an 11 speed) and still cover the overall range of gearing you need. That of course is all about personal preference and how much modification you want to do and how much money you want to spend. You may be able to get a really nice used ride with everything you already want without changing your loved original ride. I bought a 10 speed Colnago for $280 (a lucky deal since it was being sold for $450 when I first inquired) a few years back; a dream to ride, but I still prefer my old 70s and 80s friction shift bikes with only 5-6 speed rear gears. I do fit my rear gears for my type of riding, both the terrain and cadence. You should be able to customize the 6 speed cluster to the sizes you need. Thus, you may be able to utilize the same freewheel, but just change a sprocket, or 2, or 3; same could be said on the front, change the ring(s) size to suit your riding needs (a 50T is a substantial difference over a 52T ring). Both options are cheaper and easier without changing any geometry of the frame. If you are like myself you probably primarily only use 3-4 gears (6 speed) on the rear, and maybe (like myself) never use the largest rear cog and/or small front ring (or only use just the small ring). When I am up north I ride a completely differently geared bike for purposes of climbing large and steep hills that would seem like mountains to folks who grew up in Florida. I travel hundreds of feet of elevation just going from my house to town; I think "Mt Dora" in Florida is under 200' elevation, and Britton Hill (the highest land in FL) is about 350' elevation. So most gearing can be set up for the terrain, your ability, and health conditions without undergoing extreme set-up changes to the bike. I also have multiple wheels that use different gearing so I really don't need the multiple bikes I have, just a rear wheel change and I'm good; no changes in chainline using 6 speed to 6 speed swap, only thing that changes are my gear ratios. Plus, when travelling I know I have a complete rear wheel (I also carry another front wheel) in case of changing terrains, damage and breakdown; never mind having the spare tires and tubes on them.
I wouldn't mind seeing a photo of your original bike before you do any changes if you would care to post them here. It gives others a reference as to what the bike should look like and what it's original components are for rebuilding if you have some detailed pics.

Here is my super flatland Florida bike ('87 Nishiki Linear) for flying around on shorter rides; only a "straight block" (15T-19T) 5 speed rear using a 53T/48T front; definitely not geared for climbing hills or mountains, but perfect for climbing Florida's "meanest" ascents. I bought it from a friend whose back couldn't take the position; my back starts to complain after 30 miles on it:
   

[Jesper]

@EdSr did you manage to get your modification complete?
What was required to accomplish the modification?