egpotter

Hello,

I started working on my bike and have a question that I could not find a precise answer. It currently has a cup and cone bottom bracket, which has some play. I want to replace it with a sealed one. However, the current spindle lent is 124,5mm. I am not sure which BB size I should go for, 122,5 or 127. Has anyone had a similar case?

Thanks in advance

dabac

Well, how did the cranks sit with the old BB?
Dangerously close to the chainstays - get the longer one.
Do you have a front derailer?
If yes, how much travel do you have on that one?
It can be quite annoying to replace a BB only to discover that now you’ve lost a front gear due to lack of travel.

KenNC

Well are the cups and cone races damaged, or is the play due to a lack of adjustment? If the cups and cones are okay I'd just replace ball bearings, and adjust. Also, the taper on the ends of some vintage spindles can be longer than the modern standard, so if you are going from one to the other you may want to factor that in: https://www.sheldonbrown.com/bbtaper.html

conspiratemus1

Also, old cranks typically required an asymmetric bottom bracket spindle (longer on the drive side) to accommodate the thickness of 2 (or 3) chainrings. Modern cranks are shaped differently and so the cartridge BBs available since the mid-90s have symmetric spindles. Another thing to consider in getting the right size, if even possible.

Narhay

What markings does the current spindle have? You'll have to note asymmetric spindle length, taper (iso vs jis vs other), threading and bottom bracket shell width, and of course the crank.

Velo Mule

If it were me, I would stick with the cup and cone as long as there is no damage to the cups or spindle. Replace the balls, new grease and put it back together.

If the cup or spindle is damaged then it gets more interesting.

egpotter

Thanks a lot people. I will try cleaning it deep, changing the bearings and check if I can remove the play, as per your suggestions/questions it is not so easy to change it. I am quite a beginner so for sure and do not have much time right now, so for sure I will take a lot of time on this. I will post the outcome here later, as it may benefit another newbie. This is the first time I am working on and older bike. Not that anyone asked, the Bike is a Panasonic Touring Deluxe. I am very excited about getting it done.

Salamandrine 

Stop. Before you do anything at all, learn to adjust the bottom bracket bearings. Play in itself is an adjustment and nothing more. Leave the cranks on. Loosen the adjustable lock ring on the non drive side. Tighten the adjustable cup a little bit, say 1/8 turn. Tighten the lockring down again. Check the spindle for play by wiggling a crank arm. The goal is that it should be just tight enough that there is no play. If it's too loose, there will be play. If it's too tight it will bind and feel a little crunchy.

The tricky part of this is that when you tighten down the lockring, it will tighten or otherwise affect the adjustment. You have to keep tweaking the adjustable cup rotation, tightening it down, and testing for wiggle/binding again. Lots of try and fit. It might take you 10 times to get it right. You will need a lock ring wrench, and probably a pin spanner for the cup - depending on the type of BB.

Once you have mastered this, then consider taking the BB apart for an overhaul. If the spindle and cups are not pitted, I recommend you keep the existing BB.

If this sounds complicated, know that trying to replace the BB with a modern one, and getting everything to align and work properly, will by 20x harder, and you may have to buy 2 or 3 bottom brackets before you get the size right.

Salamandrine 

If you are set on replacing the BB, start by measuring the current chainline,. It should be ~ 45mm from dead center of the seat tube to the center of the middle chainring*. Besides that, measure and note the clearance distances of both the ends of the crankarms by the pedals, and the small chainring to the chainstay.

If the chainline distance is more than about 45 mm, and you have plenty of clearance to the chainstay, you might be able to get away with the 122.5mm BB. If clearance is tight already, especially for the small chainring, and you have less than 45 mm to the middle chainring, the 127 is a better bet. There's going to be some try and fit as often as not when replacing BBs.

The symmetrical vs asymmetrical thing is less a big deal than you would think, because with modern sealed symmetrical bottom brackets, the whole unit is shifted over slightly to the drive side.

124.5 mm means it is probably a 3U spindle, pretty ordinary.



* 30.7 mm from the side of the tube if it's a standard size 28.6 seat tube.

conspiratemus1

A good test for worn parts inside is, as you are advancing the adjustable cup, if you can't remove wiggling without getting binding/crunchy sounds somewhere around the circle as you turn the cranks, it is either really dirty inside or there are pits (potholes) in the spindle or (less likely) cups. If you can't find a sweet spot before tightening the lock ring (which will often need you to look for a new sweet spot as above), then the BB needs disassembly to find out why. I replace balls every time I do this, saves having to corral and scrupulously clean those fussy little balls, only to find they are not as shiny any more as they're meant to be.

If you are able to find a sweet spot, and you can find it again with tightening the lock ring, the good news is that you don't need to do anything more with it right away. Overhauling it eventually is good preventive maintenance but you can wait till you have all the tools you need to get the cranks off, say, all with some assurance that you won't need to replace any parts inside other than the balls.

Dfrost 

I’ve found that tightening a BB lock ring actually usually slightly loosens the adjustment, since it is pulling the cup away from the cone on the spindle (opposite of the effect on a wheel hub). I get pretty good results by tightening the adjustable cup just snug, then holding it in place while tightening the lock ring.

As noted, this adjustment can often be performed with the crank arms in place. Handy since they are useful in checking the adjustment.

conspiratemus1

^ Good point. With a really good BB. the tendency of the lock ring to drag the cup clockwise as you start to tighten it just exactly balances its tendency to pull the cup out of the frame, in terms of bearing tightness. So it may be better to not hold the cup in position with the pin wrench, and just let the cup go where it wants to as you tighten the lock ring against the frame.

Trial & error.

Salamandrine 

Yeah, that is true. If the adjustable cup stays put that's what happens. OTOH, if the lockring drags the cup along with it when it's tightened down, it will more likely tighten. I didn't want to write a book.... The point is, it's kind of unpredictable, and you'll never know here you're truly at until the lockring is tight.