Advise me how to replace my bottom bracket! - NOW FIXED! :)

For discussions about bikes and equipment.
jimster99
Posts: 210
Joined: 18 Jun 2012, 7:00pm

Re: Advise me how to replace my bottom bracket!

Post by jimster99 »

Thanks for the advice that it might be tricky to get the other side of the bottom bracket off. And also to turn it clockwise. Very helpful! :)

I did manage it in the end. I didn't use plusgas, just some serious welly and a home made breaker bar comprising the hollow end of my car wheel nut wrench slotted over the handle of a socket wrench, clamped over both sides of the frame with a g clamp.

Took about an hour and much loud grunting to tease it off. I had to reset the clamp every quarter turn to maintain sufficient leverage, which was fun.But nothing sheared and I didn't break any fingers or snap the frame!

The bottom bracket on the bike itself is 70mm wide. The axle is 120mm and I noticed it's not symmetrical. Sigh! Not sure how to measure this, but from one side of the axle to the highest point (the bit that the bearings rollon ) on one side was 36mm and on the other side, it was 40mm.

Removing the bottom bracket
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IMG_20230127_132315930_HDR.jpg
Partway removed
IMG_20230127_134728637.jpg
Last edited by jimster99 on 27 Jan 2023, 2:51pm, edited 1 time in total.
jimster99
Posts: 210
Joined: 18 Jun 2012, 7:00pm

Re: Advise me how to replace my bottom bracket!

Post by jimster99 »

The bottom bracket itself looks very rusty on the inside but the threads that mate to the bike look fine (albeit grease-free)
IMG_20230127_135005858.jpg
IMG_20230127_135009361.jpg
IMG_20230127_135011287.jpg
peetee
Posts: 4292
Joined: 4 May 2010, 10:20pm
Location: Upon a lumpy, scarred granite massif.

Re: Advise me how to replace my bottom bracket!

Post by peetee »

Well done. And thanks for letting us know how it went. 🙂
The older I get the more I’m inclined to act my shoe size, not my age.
Jupestar
Posts: 920
Joined: 29 Feb 2020, 3:03pm

Re: Advise me how to replace my bottom bracket!

Post by Jupestar »

jimster99 wrote: 27 Jan 2023, 2:47pm The axle is 120mm and I noticed it's not symmetrical. Sigh! Not sure how to measure this,
This may help when I had exactly this problem. although some of the BB are harder to find now.

viewtopic.php?f=5&t=105385
jimster99
Posts: 210
Joined: 18 Jun 2012, 7:00pm

Re: Advise me how to replace my bottom bracket!

Post by jimster99 »

Thanks Jupestar & peetee!

Jupestar - looking at the helpful Brucey post you linked to, I wonder if a slightly different size would actually fit in my frame? I will remeasure everything a couple more times.

If I do go with a slightly different size bottom bracket, would I be better going smaller or larger? The bottom bracket on the bike itself is 70mm exactly (I could get 68mm or 73mm easily at Halfords) and the axle is 120mm wide (Halfords has 117.5mm or 122.5mm in stock).

Or should I hold out for the exactly correct sizes?
Jupestar
Posts: 920
Joined: 29 Feb 2020, 3:03pm

Re: Advise me how to replace my bottom bracket!

Post by Jupestar »

jimster99 wrote: 27 Jan 2023, 5:11pm 70mm exactly (I could get 68mm or 73mm easily at Halfords)
68 or 73 is the size of the shell it goes into (i.e. width of the hole in the frame). Never heard of 70mm TBH. But that doesn't mean it doesn't exist.
slowster
Moderator
Posts: 4629
Joined: 7 Jul 2017, 10:37am

Re: Advise me how to replace my bottom bracket!

Post by slowster »

Jupestar wrote: 27 Jan 2023, 6:30pm Never heard of 70mm TBH. But that doesn't mean it doesn't exist.
70mm is the width of italian BB shells, but obviously that is not what the OP's bike has, because italian BBs and shells use normal (not reverse) thread on both drive and non-drive sides. It's not always even necessary to measure the shell to discover if it is an italian bottom bracket; often you can rely on the bottom bracket letting you know by unscrewing itself mid-ride.

My guess is the OP's bike has a 68mm shell (but maybe with not great manufacturing tolerances).

https://www.sheldonbrown.com/cribsheet- ... ckets.html
Jupestar
Posts: 920
Joined: 29 Feb 2020, 3:03pm

Re: Advise me how to replace my bottom bracket!

Post by Jupestar »

slowster wrote: 27 Jan 2023, 6:38pm My guess is the OP's bike has a 68mm shell
I agree, but measure twice, buy once. It's a road bike 68 makes sense. Axle length is basically a guestimate..

Good info again on the 70mm....
jimster99
Posts: 210
Joined: 18 Jun 2012, 7:00pm

Re: Advise me how to replace my bottom bracket!

Post by jimster99 »

Thanks - the battery on my digital calipers was flat so I had to eyeball it with the manual measurement. It's possible that instead of "manufacturing tolerance" there may have been "user tolerance" :) I'll double check again tomorrow!

PS it's a vintage Carrera Vulcan MTB (from Halfords) so I don't think it will have fancy non-standard sizes.

PPS Also I measured the actual bottom bracket on the bike (without the cups installed on each end). Maybe I should have allowed for the cups also? If so, that would probably jump the size from 70 to 73 I suspect!
alexnharvey
Posts: 1923
Joined: 10 Jan 2014, 8:39am

Re: Advise me how to replace my bottom bracket!

Post by alexnharvey »

jimster99 wrote: 28 Jan 2023, 12:43am Thanks - the battery on my digital calipers was flat so I had to eyeball it with the manual measurement. It's possible that instead of "manufacturing tolerance" there may have been "user tolerance" :) I'll double check again tomorrow!

PS it's a vintage Carrera Vulcan MTB (from Halfords) so I don't think it will have fancy non-standard sizes.

PPS Also I measured the actual bottom bracket on the bike (without the cups installed on each end). Maybe I should have allowed for the cups also? If so, that would probably jump the size from 70 to 73 I suspect!
The shell width measurement excludes the cups.
jimster99
Posts: 210
Joined: 18 Jun 2012, 7:00pm

Re: Advise me how to replace my bottom bracket!

Post by jimster99 »

Woohoo! New bottom bracket on and the bike is perfect again. Thanks so much all :)

I remeasured the bottom bracket shell in the daylight and new batteries back in the digital caliper, and to my surprise, it was a 68mm! I thought I had been so careful measuring it to 70mm with analog calipers. The axle was still 120mm and non-symmetrical (by about 4mm), so I went with a 68x122mm symmetrical bottom bracket from Halfords (for the bargain price of £10) which was the closest size I could find for immediate availability. It did have a small scratch gouged in the middle of the cartridge which worried me whether it would become a rust spot, but I couldn't face another trip to Halfords tomorrow to exchange so I decided to live with it.

Anyway installing the new bottom bracket was super simple. I cleaned the threads with some Holts disc brake cleaner & a mythical lint free towel, put a bit of copper grease on the threads, it slid right on, and everything just works. Amazing!

Only thoughts: (i) I'm surprised the front gear didn't need the indexing redoing given I changed the axle size and symmetry, perhaps it will once I've taken it for a proper ride and (ii) I did wonder if a prevous owner had installed a wrong size bottom bracket on? It seems fairly unlikely that a Halfords Carrera bike would have something so incredibly non-standard as a 120mm, and the 122m fitted perfectly.
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