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PostPosted: Tue Nov 17, 2015 6:06 pm 
Old School Hero

Joined: Mon Jun 09, 2008 9:55 am
Posts: 205
Location: London
Mine always come loose when I install a new bottom bracket, probably because I tend to go over-the-top with the grease. Then, when I tighten it up a second time, everything is fine, no more coming loose.


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PostPosted: Tue Nov 17, 2015 6:14 pm 
Retro Guru
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Joined: Mon Mar 26, 2012 5:21 pm
Posts: 635
pigman wrote:
I would have thought there was more chance of an English BB coming loose...

As Shaun says, Italian BB are prone to coming unscrewed because of "mechanical precession".

Your pedals are threaded as they are, for the same reason.


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PostPosted: Sun Nov 22, 2015 1:14 pm 
Dirt Disciple

Joined: Sun Feb 12, 2012 1:55 pm
Posts: 94
Location: Blue Ridge mountains
I have a frame with an Italian BB that would start to unscrew on long climbs. I reinstalled with some plumbers teflon tape on the threads and it has not moved for several years now. Probably depends on the quality of the frame and the skill of the person threading the BB if yours stays tight or not.


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PostPosted: Mon Nov 23, 2015 5:21 pm 
Old School Hero
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Joined: Mon Oct 15, 2012 11:12 pm
Posts: 215
Location: Herts/Essex border
British threaded BBs are the correct engineering solution as pedalling forces tend to tighten up the cups on both sides. The chain set side of an Italian BB tends to unscrew as the cup that side tightens up conventionally i.e. not reverse thread as British BBs.
Italian bikes usually have their BBs glued in with something on assembly to stop them unscrewing. This can make them a real problem to remove later so when I get them out I usually (foolishly) over compensate by applying too much grease to the cup threads on reassembly. I have had two occasions when the BB unscrews itself on the chain set side. Once it jammed the crank and rear wheel solid and the other prevented the front derailleur functioning. Reassuringly on neither occasion did the BB totally unscrew itself and fall in the road ! Solution was to strip the BB down and remove the excess grease and then tighten up hard.


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 Post subject: Re:
PostPosted: Mon Nov 23, 2015 11:07 pm 
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Joined: Sat May 22, 2010 10:33 pm
Posts: 2210
Location: Suffolk
My one bike with an Italian thread BB has plenty of miles on it and it does jot work loose hut then again I torque the ds cup to 70 Nm to be sure.


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PostPosted: Mon Nov 23, 2015 11:33 pm 
Old School Hero

Joined: Tue Apr 22, 2014 11:44 am
Posts: 166
Location: Saaarf London
I'm working at a London bike shop while I'm 'between jobs' in aviation. Oddly enough I fitted a new Miche 103mm BB to a customer's repainted Mercx frame a couple of weeks back; I used a brand new cutter on the shell, lots of grease and bolted it up nicely and tight. A week later it came back with the r/h cup unwound and jammed up against the crank. Not good. So I whipped it all out and had a good look at it, just a bit of scuffing around the r/h crank but nothing more. I'd not heard of mechanical precession in relation to BB's, only regarding gyroscopes in autopilots etc, but it made sense when I researched it. So I did as others have done - cleaned the excess grease off and refitted it and so far it's been ok. Interesting stuff.


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PostPosted: Tue Nov 24, 2015 11:25 am 
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Joined: Sat May 22, 2010 10:33 pm
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Location: Suffolk
I use anti seize on on mine. The BB cups wind in by hand. The trick is 70Nm that is how you avoid unwinding. Never had one unwind (whether it be mine or a customers) because I do it this way. Nice and tight is not 70nm it could be alot less.

You should always use grease or anti seize on BB threads as in time they can become a pain to remove.


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