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| cb1rocket |
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cb1rocket
World Chat Champion
Joined: 30 Jan 2010
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 Posted: 22:35 - 28 Jul 2013  Post subject: Bottom bracket |
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Hi
Where does the measurement after the usual 68 come into?
I have been looking to replace my bottom bracket but need to know what size to get.
I keep seeing sizes like 68 - 120, 68 - 114 etc
What is the 2nd (ie 120) group of number referring to?
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| stidds |
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stidds
Two Stroke Sniffer
Joined: 17 Dec 2012
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| cb1rocket |
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cb1rocket
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| Posted: 22:10 - 29 Jul 2013 Post subject: |
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| stinkwheel |
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stinkwheel
Bovine Proctologist
Joined: 12 Jul 2004
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| Posted: 23:12 - 29 Jul 2013 Post subject: |
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You also need to know what thread type it has. English or Italian.
An English thread has one side standard thread and the other reverse thread. An Italian has both standard thread.
Also the fitting. Octalink or square taper.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles. |
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| AndyB1989 |
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AndyB1989
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| stinkwheel |
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stinkwheel
Bovine Proctologist
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| Posted: 10:16 - 30 Jul 2013 Post subject: |
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| AndyB1989 wrote: | If you are going from a loose cup and cone square taped to a sealed unit it is not the total length you need to measure as these are often not symetrical and measuring total length can fuck up your chain line ,
what you need to do is make sure the amount that sticks out on the drive side is equal on the new BB. |
But equally, the distance the crank sits on the taper varies from brand to brand anyway so you just have to suck it and see. Measuring, with the best will in the worlkd, will only put you in the ballpark. The stated length is mostly irrelevant other than for comparing two BBs of the same make and type.
I keep an old, knackered shimano sealed unit at home. If I'm swapping out a loose or non-shimano BB, I fit it then see how far out the chain line is. I then add or subtract twice the difference to order in the new shimano one.
So my knackered one is 113mm. If my chain line is 1mm too close to the frame on that one, I order a 115. If it's 2mm too far out I order a 109 (well, a 108, you never see a 109).
It's a bit of a buggeration but the only way to be sure if chainline is critical (which in fairness, on bikes with multiple chainrings and deraileurs, it can afford to be a fair way out). On a fixie, single speed or hub gear bike it's more important.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles. |
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Old Thread Alert!
The last post was made 11 years, 358 days ago. Instead of replying here, would creating a new thread be more useful? |
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