polynimbus

Trying to replace the crank set on an old Shogun Prarie Breaker II, and am having a tough time finding info about this style of BB (It uses nuts to attach the crank instead of a bolt). I have tried 3 local shops, but they don't seem interested/know much about threaded stud style BB's. The crank arms they sell are all "designed for bolts, not nuts" on the pedal side, but I don't know if that matters.

I'm hoping this is a quick/easy question for someone who has dealt with older sets, but can I just use a standard JIS crank arm or does the nut need specific crank arms to not bottom out before getting tight on the taper? It's a 3 ring crank set on there now, and I would like to stay at 3 if the offset will still work with a new set.

Also, if I were to replace the BB entirely and go with a more modern JIS mount style, is the BB shell a standard thread on that old style BB? I don't want to tear it apart to find out if it's going to be tough to find new components. Any info will be appreciated, I am just getting in to the more complicated parts of rebuilding.

Litespud

So, if I understand it, you want to replace the cranks, but retain the BB, which uses nuts rather than bolts, and you're having a hard time finding replacement cranks that use nuts, given that bolts are essentially the standard fastening method these days? Have I got that right? This issue is finding a crankset compatible with your BB?

Assuming that your BB shell threads are some standard thread (and I'd be willing to bet that it's a standard English thread (1.37" x 24tpi)), and you're replacing the crankset anyway, I'd invest the extra ~$20 and buy a new BB that matches your new cranks. Using a modern - or at least more mainstream - BB will vastly open up your crank choices. You might need the requisite tool to remove your old BB to confirm, but if you're going to work on your bike, you should get this anyway just for routine maintenance

JohnDThompson 

The crank arm doesn't care if it's mounted with a bolt or a nut. JIS taper is JIS taper regardless of mounting type. The concern is whether the axle length is appropriate for whatever crank you want to use.

dedhed

Doesn't matter whether it uses bolts or nuts as long as the shell width & threading, spindle length, and taper are correct. Some cartridge BB come with bolts some you have to reuse the old ones or buy a couple if coming from a nutted one.
The crank doesn't care that it's a bolt or nut holding it on, just that it's tight.

What's wrong with the old crank that you can't just reuse it on a new BB?

Cranksets determine the BB spindle length so you determine the crank to be used before selecting the BB. A new crank may or may not work with your existing BB spindle length. It's always worth a try and then if it works great if it doesn't then buy the one needed.
That Shogun is without a doubt English threaded but you'll have to measure BB shell width to see if it's 68mm or 73mm

Do some research on chainline, and BB spindle length.

Fissile

All explained in the Gospel of St. Sheldon. https://www.sheldonbrown.com/bbtaper.html

I agree with the other other posters who say you should swap out the old BB for a modern cartridge BB. You can find a perfectly serviceable modern BB for about $20 delivered.

dsbrantjr

I fail to understand the difference between putting a nut onto a stud or a bolt into a hole to hold a crank onto a BB taper. I have swapped stud-type cup-and-cone BBs for bolt type cartridge BBs using the same cranks without any thought or special process, except for getting the correct length of course.

cb400

You should take it apart anyway to find out whether or not the cups/spindle are pitted, if any are then getting a cartridge bottom bracket is a no-brainer.

polynimbus

That is correct, I wasn't sure how universal JIS cranks were but it sounds like they should work. And the shell thread is good info, I will definitely pull it apart and see if I can get a new one.

One crank is missing, otherwise I would be fine reusing them. I figured if I am getting new crank I might as well update the BB.

I think that is a good plan, and thanks for the specific reference. That helps a bunch.

The only thing I was worried about was the width of the new crank, since you can tighten a bolt clear down to the start of the taper if necessary, but the nut will stop where the threads on the stud end (which is still 1/4" from the start of the taper). I assumed this was fine since you shouldn't be that close to bottoming out, but I wanted to double check I wasn't doing something dumb.

Thanks for all the replies, I will definitely take it apart and get a new BB to match a new crankset.

dsbrantjr

It is kind of academic since you plan to replace the BB, but you could put a washer under the nut if needed.

Moe Zhoost

I'd stay away from those shops. Either the mechanic is inexperienced or, if you talked to a sales person, they were too lazy or dumb to refer your question to a mechanic.

Barry2 

Just a thought - Are you sure the Crank you have is a JIS taper?
Identifying a taper type can be tough. Some Cranks were made in more than one taper type.

Now, if you replace the cranks and the BB at the same time, that issue goes away.
Plus you don't have to go looking for a JIS replacement crankset. That alone might save you the cost of a new BB.

All the best

Barry

Fissile

Then he's going to be staying away from pretty much every bike shop. The days of hole-in-the-wall type bike shops that employ crotchy mechanics named Sheldon who could repair your 50's era Mingus racer because he has a box full of French threaded jockey bolts somewhere in the train-wreck of a workshop for $2 are long gone. Today bike shops need to compete with the net and big-box stores to stay in biz. That means selling and servicing new bikes.

Narhay

It took working on about 5 different bikes in my spare time as a hobby with a square taper bb to find one with a nut instead of a bolt. Square taper bb are still very common and to not have come across one as a bike professional tells you a lot.

Moe Zhoost

We're talking about nutted square taper spindles here, which are very common. Even crotchless mechanics should be able to handle them.

Bill Kapaun

Note that this refers to "Bolt Type", inferring there are other types.
It doesn't matter as long as you have the PROPER nut or bolt.
https://www.huskybicycles.com/bicycl...bolt-type.html

alcjphil

In my experience, everybody has a crotch. Square taper bottom bracket spindles using nuts are very common. Any bike mechanic who is unfamiliar with them might well be crotchless, but I am not comfortable with finding out

Bill Kapaun

Might be some conjoined twins.....

scott967

I had that nut-style BB on my 85 Fuji Touring III. Never gave any thought to it when swapping cranks, but it was set up for a triple and had some chainline issues when installing a 2X on it. Now it has a UN55 on it. Getting the drive side fixed race off was a bit-- but eventually got it off. Got some flat stock for each side and ran a threaded bolt through it so I could lock the wrench on the race then started hammering that sucker.

scott .
.

polynimbus

Thanks for the help everyone, I am learning a lot here.

I got the old spindle out and it all makes sense with the dimensions from Sheldon's site, but I am a bit perplexed at finding a new spindle/BB. The spindle size I removed is a 3T, which is assymetric, which means I would need a 130mm symmetric spindle in order to keep the chainline correct. All of the cartridge and spindle options I find top out at about 123mm, which makes me think I might be misunderstanding something. It's a 68mm shell, and english threaded.

The bearings are in decent shape (very slight brinelling is the only issue I can see) so I might just clean these up and put them back together and get a new set of cranks and call it a day. I still would like to understand how to go about getting a modern external bearing BB, however. Is there a way to get the chainline out to match the existing location but use a shorter, modern crank? The chainline measured a pretty standard 47mm, so it seems like it should be possible, I'm just not sure what I'm missing.

Bill Kapaun

The longest cartridge BB's I've seen are 127mm.
The 3T has an abnormally long DS length.
Modern cranks tend to use much shorter BB's than the "old stuff".
The spindle I linked to in my 1st post is a 3T.