Originally Posted by
bikingshearer
Because you have had the good fortune to have had the fixed cup tightened until it screamed for mercy and/or had pipe thread tape put on the threads and/or had it held in place by LocTite (blue, not red, unless you never want to be able to remove it ever again, although some say you should never ever use any kind of LocTite for this application). It is not hard to have this never happen, but it is also not hard to slip up and end up doing the Fixed Cup Unscrewed Walk of Shame.
Some of us (me and apparently [MENTION=168558]Drillium Dude[/MENTION] and [MENTION=150273]thinktubes[/MENTION] included) have had the unpleasant experience of installing an Italian BB, not doing one or more of the above, and having the fixed cup come loose 10 to 15 miles into the first ride. It happens because, as the drive side bearings spin with the BB axle, the outer part of the bearing is trying to push a right-hand threaded cup in the direction you would spin it to make it come out. (By contrast, with a left-hand threaded British fixed cup, the bearings are trying to push the cup in the direction that tightens the cup.) It sounds like there is no way that tiny little bit of force could do more than loosen the cup more than a tiny little bit, but multiply that tiny little bit of movement by 70 to 100 rpm and multiply that by however many minutes it takes you to go 10 to 15 miles, and it adds up to a walk home or a phone call for a pick up.
I've been there (and boy, did my riding buddy give me rations of cr*p for it), and it sounds like Drillium Dude and thinktubes have, too. In my case, it happened exactly once, and I swore a mighty swear that it would never happen again. I bet that is true of these other two fine gents as well.
[MENTION=168558]Drillium Dude[/MENTION] and [MENTION=150273]thinktubes[/MENTION] too
Fixed cups loosening while riding was more common during the 1970's when components and frame quality was lower. Undersized threads on the cups and oversized BB threads, especially when they'd been chased by someone who didn't have good tools or didn't know how to use them resulted in loose fits.
I have had and have seen fixed cups on French bikes come loose far more often than on Italian bikes. Fortunately I sensed that the BB was coming loose and was able to tighten the cup by hand (several times) enough to get back to the car or home. After that I started using Loctite on cups that came loose.
When I overhaul BBs I make sure that the threads are clean and free of crud and rust. I have set of VAR BB taps and chase the threads if needed. Before reassembling, I run the cups in by hand. If they are too loose, I apply some Loctite Blue - amount depends on looseness. The threads have to clean and grease free for Loctite to work well.
One of my best tool investments was a VAR Fixed Cup BB tool. When I tighten fixed cups they stay tight!
Here's a cheap, easy solution per Sheldon Brown RIP. A bolt, nut and some washers.
I was out riding with a friend an number of years back. He was on his 2006 Lemond Sarthe with Bontrager outboard bearing cranks. He kept saying his cranks were feeling weird. We stopped and I discovered the the drive side BB bearing had come loose. I tighten it by hand and we made it to a high end bike shop a few miles away. The so called mechanics put the bike up on a stand but couldn't see the problem.
That was the first time I'd ever seen an outboard bearing BB up close but I was able to show them how to tighten it. DOH! Those BBs come loose too.
verktyg
