Linear Bottom Bracket Issue

[a.twiddler]

Flushed with success by my bar end gear lever conversion yesterday, today I thought I would change the bottom bracket on my Linear. It has been a bit rough for a while, but still usable. Still, I thought, why not start the New Year with a smooth running transmission. I had taken the cranks off a couple of weeks ago to measure up and see what tools I would need, then put them back on again until my order arrived. Although the bottom bracket tube is welded to a couple of plates which are clamped to the frame, it looks like a standard BB55 type cartridge bottom bracket. The shell width is 68mm, the spindle length is 127.5mm, and the cups take a standard Shimano type tool.

I expected everything to be tight but having changed a couple of similar BBs before I just gave it some time and oil. I managed to loosen both sides (I thought) but after a while I found that everything turned stiffly but didn't unscrew. I tried both sides in turn but although they moved, they didn't unscrew at all. It was only when I stood over the frame and turned the tool on one side that I realised that the other side was turning as well. So either I have stripped both threads (which I think is unlikely -I'm not that strong, and why would both sides turn) or this is some type of replacement bottom bracket which screws into itself to fit frames with already damaged threads. The bottom bracket shell is an aluminium tube probably over 25 years old so this could be possible. Until I get it out I won't know what it is. At the very least I will probably need to find another Shimano tool to see if I can separate the parts.

I am open to suggestions. Meanwhile I am going to trawl the internet to try and find out more.

Looking on the bright side, I've managed to get out on my upright earlier on this clear and frosty day and blow away some cobwebs.

 

[Ajax Bay]

I tried both sides in turn but although they moved, they didn't unscrew at all. It was only when I stood over the frame and turned the tool on one side that I realised that the other side was turning as well. . .
why would both sides turn

I wonder if the two parts of the cartridge BB (eg UN-55) have seized together - it's a close fit when the left side is screwed in. Then when you unscrew the left side (normal anti-clockwise) that seeks to turn the right hand side (would have to be loose) - and of course that unscrews the 'same' way (but looks clockwise from the right side). But the two sides would pull away from the BB shell after a turn or two - presumably that didn't happen?

 

[a.twiddler]

Aargh! Well I just guess I'll just have to suck it up and accept that I'll be camping on the shores of Lake Disappointment tonight. No quick fix to this, I suspect, following my investigations on t'internet. Either the Linear already has a "threadless" bottom bracket installed in which case I need to get hold of another Shimano BB tool to get it out (or indeed even confirm that one is fitted) or I have with my own blundering ministrations messed up the threads all by my self. I will either have to get in the queue for my not so local bike shop to get the threads chased or just fit a threadless BB. My original intent was to bung in a new BB and go a'recumbenting (even if just round the block) for a ride on the last day of the year. Ain't gonna get done in the last 15 minutes of 2020 now.
Well, not to worry, it'll get done in due course. Meanwhile I am investigating the properties of this rather nice Aspall's cyder which I received for Christmas. Happy New year, folks!

 

[Gunk]

Sounds like a threadless BB, the non drive side is threaded, so use your socket on that and try some needle pliers to stop the other side spinning. If that doesn’t work, you will need a second socket.

 

[a.twiddler]

The more I think about it, the more I think it is threadless. The needle nose pliers suggestion sounds good! They might just give enough friction to get the threads moving. Otherwise, ebay may provide a Shimano BB tool.

 

[a.twiddler]

The mystery is solved. The needle nosed pliers didn't work last night, so I looked on ebay for an extra Shimano BB tool. Disappointingly, the delivery dates were towards the end of next week, or the week after. However, the dreaded Halfords was open on New Years' Day so I nipped out and picked one up from our local branch. After an hour or two of sweating and straining with little to show for it I drenched it in yet more oil (plenty in there from yesterday) and left it to soak.

I returned later and bolted some washers to the spindle ends to retain the BB tools against the cups. Bit by bit they loosened, needing the bolts easing to give them space to unscrew. At last one cup came loose -on the right hand end. I thought that was a bit strange, as the loose cup ought to be on the left hand end, with a right hand thread. The cup on the right hand end ought to to have a left hand thread, but the loose one had a right hand thread. I pulled the bottom bracket assembly out and noted that it was threadless, and in the wrong way round despite being marked with arrows for L and R. That explains why nothing started to loosen until the main body of the BB began moving! I could have been grappling with this for a lot longer than I did. I have been lucky there.

I wondered why a threadless BB had been fitted, let alone the wrong way round. I had a new threaded BB ready to fit, so I decided to give it a try. I could see that the threads in the shell didn't look too bad though one or two on the drive side looked slightly rough. I tentatively screwed the left hand cap in and it felt OK. I did the same with the main body but it felt a little reluctant. I gave the shell a flooding with GT85 and cleaned up the inside with a cloth. I tried the main body again and it went most of the way in before I had to use much force. It seemed to be cleaning up the threads as it went in. I took it out and cleaned up some bits of swarf, gave the shell a good cleaning again and decided to take the plunge. If it didn't stay in place and came loose I would have to buy another threadless one, but if it proved to be OK then I hadn't lost anything.

I gave the threads a good greasing (bearing in mind it was steel screwing into aluminium) and the main body went most of the way in, a bit stiff but without an excessive amount of effort. It tightened up well, and the left end went in smoothly and nipped up OK too.

The bike is back together now, just awaiting a test ride.

 

[Ajax Bay]

So the previous installer had put a threadless BB as a friction fit into a threaded 1.37 x 24 BB shell, and the wrong way round. You couldn't have guessed that. Chasing the threads first would seem more prudent if you were in less rush. Best of luck.

 

[a.twiddler]

An interesting situation, and a learning episode. The old BB looked inscrutably like any square taper cartridge jobbie with Shimano ends. As my X-ray vision isn't what it used to be, there was potential for all sorts of woe, maybe even damage to the shell. So I have been lucky that it came out without the application of all sorts of brute force and ignorance, and even the threads are functional.

The puzzle will probably never be solved as to why a threadless set was put in in the first place, and particularly the wrong way round. The only clue to a threadless BB being fitted might have been that the outer diameter of both ends is wider than the inner diameter of the shell, while on the new threaded one, only the drive side end is larger than the inner diameter. Easy to miss if you are not looking for it. The inboard side of the ends of the old BB has a chamfer, but the shell has not been given a chamfer to match, which I would think a bike shop would have done, as well as putting it in the right way round.

Despite all this home mechanic bodgerie it functioned well enough as a bottom bracket. There was a little play in it showing it was due for replacement soon, but could have gone on for hundreds of miles yet, until I tried to get it out. It was certainly not in danger of coming loose!

It just goes to show that with an older bike you don't know what has been done in the past by one of several owners. Also, if something can be fitted the wrong way round, someone, somewhere will do it.

 

[a.twiddler]

One disappointing thing that I found out in my quest for a replacement bottom bracket was that the redoutable Shimano UN-BB55 range has been discontinued. Although I haven't had to replace many bottom brackets over the years this was the "go -to" one for decent quality at a good price. Where there have been the last stocks in the size I needed, the price has at least doubled from the price I paid for one at the beginning of last year. The current Shimano equivalent seems to have a lower build quality for the price of a BB55 a year ago. Maybe for all normal purposes the replacement in the range will be fine.

I can't help thinking though that it's another example of older tech like square taper BBs going the way of screw-on freewheels in that they are less easily available in medium to high quality, only in potentially lower grades. Just because components like these tend to be used in utility type bikes, it shouldn't mean that the quality of materials, seals etc should suffer. All my bikes have square taper BBs, so make of that what you will.

Any how, I plumped for a FSA RPM BB-7420ST due to decent reviews for the price, and will see how that works out.

 

[Ajax Bay]

No, I think the UN-55 replacement, the UN-300 is the same standard, spec and price. Stronglight 400 also looks fine and (?) better vfm than FSA.

 

[a.twiddler]

Time will tell how the FSA BB lasts.

 

[a.twiddler]

Meanwhile, I've managed to get out for a preliminary test ride and can report no strange noises. It's free running, and the difference between even the small amount of play in the old one and the solid feel to the transmission now is noticeable. So in that respect overcoming the earlier tribulations has produced a good result. If I can get through this year without issues with it I can count it a success. Need more miles now to give it a thorough shakedown.