a.twiddler
Veteran
I Ain’t Afraid of no...Brompton Bottom Bracket!
Or, fools rush in.
As with most of life’s triumphs and disasters this episode started with pondering about what if…
With the standard bottom bracket an early type 50T chainring with a small inner ring attached works with the bike unfolded but when you fold it the slightly domed chainring bolt heads just contact the paint on the chainstay.
What if… I took the bottom bracket out, put a spacer (which I have in my bits box) on the drive side and reassembled it? A cheap and cheerful modification at just the cost of a FAG tool from ebay. There seems enough clearance to allow the crank on the non drive side to move inwards a corresponding amount without clashing with the folded frame.
I’ve changed a few bottom brackets in recent years, mostly Shimano, but apart from a bit of brute force and ignorance needing to be used to get some of them started, it has all gone well. This FAG bottom bracket with its plastic fantastic cups should be easier, I thought, with no possibility of corrosion seizing them in. I ordered a FAG tool which had a hexagonal nut on one side, and the six prongs to engage with the bottom bracket on the other.
The day came. Selection of washers tensioned with the spindle bolt -check. FAG tool to be held in place by said washers to avoid slipping and chewing up the plastic (not too tight, to allow the cup to move outwards ) -check. 12” Hercules adjustable spanner -check. Small hide faced mallet just in case -check. I started with the non drive side. It wouldn’t move with just hand pressure but after a couple of gentle taps with the mallet I was able to move it by hand.
It was looking promising. I managed half a turn then slackened off the spindle bolt, another quarter turn then it became harder to turn. Another push on the spanner and “t’chink” and the ring turned freely. Oh. I undid the spindle bolt, removed the FAG tool and the plastic ring fell off. The name of Kinnel was heard throughout the land, or at least in my garage, as in what the Kinnel is going on?
Had someone overstrained the mounting rings when putting it on? Have they become brittle from age or exposure to sunlight? There were no marks on them, or fading. I thought that as I had another chance to get it out on the drive side, I would worry about getting the remains of this cup out when I’d got the rest out. Maybe one side might be unusually weak, surely the other side would be OK.
So, the same procedure on the other side. Again, it started to turn freely then without warning this side too snapped like a carrot. What in the name of the various flying fudpuckers is going on? Is it made of cheese? (Mmm, cheese).
I was a bit perplexed. I’d not used much more leverage than a fairy fart this time and yet the plastic had given way.
Over the next few days I tried various things. Drilling the plastic and tapping steel pins into it, then trying to rotate the cups by tapping with a small hammer and screwdriver. Eventually resorted to a G clamp and various sockets to spread the load, trying to press the centre out, which did move one of the bearings slightly. Since the bottom bracket wasn’t going to be re usable I ordered a Shimano one. Since the original chainsets were ISO, according to Sheldon Brown they should fit 4.5mm or so further out on the Shimano taper, being JIS, which ought to give the correct clearance if I got the size right.
I tried drilling lots of small holes in the non drive side cup hoping to weaken it enough to enable the innards to be bashed through using a lump hammer on the opposite spindle but only succeeded in slightly mushrooming the end of the spindle. I was more worried about damaging the frame and particularly the suspension spindle by over stressing it.
Finally I visited a long established bike shop in a nearby town where after some sucking of teeth and intakes of breath was suggested to try a local engineering works to get it pressed out. I did try there but was booked up for weeks ahead. Sunk in gloom, I put it aside it for a while.
A few days later I called in at a car accessories place which had a bike workshop to see if they had any tools I could use to get the blighter out but they suggested I brought it in to let them look at it. I took it in without much hope together with the new BB as if they got it out they would probably have to clean up the threads, so might as well fit it. “Give us a week” they said.
Two hours later I got a phone call. “Bike’s done.”
I went to collect it immediately, as I wanted to find out how they’d managed it. They took the bearing seals out and after crowding the ball bearings together were able to remove one then all of them and take the spindle out. I could probably have done that part myself. Next they used some kind of cutter to break up the hardened steel outer race and remove it. That’s something I don’t have the tools to do.
I was so glad to have got something fixed that I’d been fretting about for two weeks that to me, what I paid them was a bargain.
I reassembled the bike with the 44T single ring as a 3 speed as before. I’d tried the double and still had clearance problems when folded. I’d failed to account for the 118mm Shimano BB unit being more symmetrical than The FAG one, so the spindles were about the same both sides.
Normally I tend to think, “if it ain’t broke, don’t fix it” but over the last couple of years of recumbenting I’ve made things work that I’d previously not thought possible. Sooo...
What if ..what if… I took the bottom bracket out, put a spacer (which I have in my bits box) on the drive side and reassembled it?
Groundhog Day?
Not going to try that for a while.
Now if anyone mentions FAG bottom brackets to me it’s time to Be Afraid...Very Afraid…
Shimano is the way to go.
Or, fools rush in.
As with most of life’s triumphs and disasters this episode started with pondering about what if…
With the standard bottom bracket an early type 50T chainring with a small inner ring attached works with the bike unfolded but when you fold it the slightly domed chainring bolt heads just contact the paint on the chainstay.
What if… I took the bottom bracket out, put a spacer (which I have in my bits box) on the drive side and reassembled it? A cheap and cheerful modification at just the cost of a FAG tool from ebay. There seems enough clearance to allow the crank on the non drive side to move inwards a corresponding amount without clashing with the folded frame.
I’ve changed a few bottom brackets in recent years, mostly Shimano, but apart from a bit of brute force and ignorance needing to be used to get some of them started, it has all gone well. This FAG bottom bracket with its plastic fantastic cups should be easier, I thought, with no possibility of corrosion seizing them in. I ordered a FAG tool which had a hexagonal nut on one side, and the six prongs to engage with the bottom bracket on the other.
The day came. Selection of washers tensioned with the spindle bolt -check. FAG tool to be held in place by said washers to avoid slipping and chewing up the plastic (not too tight, to allow the cup to move outwards ) -check. 12” Hercules adjustable spanner -check. Small hide faced mallet just in case -check. I started with the non drive side. It wouldn’t move with just hand pressure but after a couple of gentle taps with the mallet I was able to move it by hand.
It was looking promising. I managed half a turn then slackened off the spindle bolt, another quarter turn then it became harder to turn. Another push on the spanner and “t’chink” and the ring turned freely. Oh. I undid the spindle bolt, removed the FAG tool and the plastic ring fell off. The name of Kinnel was heard throughout the land, or at least in my garage, as in what the Kinnel is going on?
Had someone overstrained the mounting rings when putting it on? Have they become brittle from age or exposure to sunlight? There were no marks on them, or fading. I thought that as I had another chance to get it out on the drive side, I would worry about getting the remains of this cup out when I’d got the rest out. Maybe one side might be unusually weak, surely the other side would be OK.
So, the same procedure on the other side. Again, it started to turn freely then without warning this side too snapped like a carrot. What in the name of the various flying fudpuckers is going on? Is it made of cheese? (Mmm, cheese).
I was a bit perplexed. I’d not used much more leverage than a fairy fart this time and yet the plastic had given way.
Over the next few days I tried various things. Drilling the plastic and tapping steel pins into it, then trying to rotate the cups by tapping with a small hammer and screwdriver. Eventually resorted to a G clamp and various sockets to spread the load, trying to press the centre out, which did move one of the bearings slightly. Since the bottom bracket wasn’t going to be re usable I ordered a Shimano one. Since the original chainsets were ISO, according to Sheldon Brown they should fit 4.5mm or so further out on the Shimano taper, being JIS, which ought to give the correct clearance if I got the size right.
I tried drilling lots of small holes in the non drive side cup hoping to weaken it enough to enable the innards to be bashed through using a lump hammer on the opposite spindle but only succeeded in slightly mushrooming the end of the spindle. I was more worried about damaging the frame and particularly the suspension spindle by over stressing it.
Finally I visited a long established bike shop in a nearby town where after some sucking of teeth and intakes of breath was suggested to try a local engineering works to get it pressed out. I did try there but was booked up for weeks ahead. Sunk in gloom, I put it aside it for a while.
A few days later I called in at a car accessories place which had a bike workshop to see if they had any tools I could use to get the blighter out but they suggested I brought it in to let them look at it. I took it in without much hope together with the new BB as if they got it out they would probably have to clean up the threads, so might as well fit it. “Give us a week” they said.
Two hours later I got a phone call. “Bike’s done.”
I went to collect it immediately, as I wanted to find out how they’d managed it. They took the bearing seals out and after crowding the ball bearings together were able to remove one then all of them and take the spindle out. I could probably have done that part myself. Next they used some kind of cutter to break up the hardened steel outer race and remove it. That’s something I don’t have the tools to do.
I was so glad to have got something fixed that I’d been fretting about for two weeks that to me, what I paid them was a bargain.
I reassembled the bike with the 44T single ring as a 3 speed as before. I’d tried the double and still had clearance problems when folded. I’d failed to account for the 118mm Shimano BB unit being more symmetrical than The FAG one, so the spindles were about the same both sides.
Normally I tend to think, “if it ain’t broke, don’t fix it” but over the last couple of years of recumbenting I’ve made things work that I’d previously not thought possible. Sooo...
What if ..what if… I took the bottom bracket out, put a spacer (which I have in my bits box) on the drive side and reassembled it?
Groundhog Day?
Not going to try that for a while.
Now if anyone mentions FAG bottom brackets to me it’s time to Be Afraid...Very Afraid…
Shimano is the way to go.
