Bicycle Mechanics - Unscrewing Peugeot bottom bracket
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05-20-09, 10:23 AM
So I've got an early 70's Pug UO-8. The fixed cup (drive side) keeps unscrewing during pedaling, and even when it's "tight," it clunks (it's not the cotter - you can feel the other side move up while that side moves down and vice versa). Is there any way to get it REALLY tight without removing the crank? I don't have an adjustable wrench (or any other wrench for that matter) that is big enough to fit, yet narrow enough to get behind the chainrings. Any ideas?
05-20-09, 12:24 PM
parktools use to make a wench for this job, but not any more.your lbs may have one,or check ebay for one. if one not found yes you will have to remove the crank.
05-20-09, 01:58 PM
So I've got an early 70's Pug UO-8. The fixed cup (drive side) keeps unscrewing during pedaling, and even when it's "tight," it clunks (it's not the cotter - you can feel the other side move up while that side moves down and vice versa). Is there any way to get it REALLY tight without removing the crank? I don't have an adjustable wrench (or any other wrench for that matter) that is big enough to fit, yet narrow enough to get behind the chainrings. Any ideas?How did you get the fixed-cup "tight"? And exactly how "tight" did you get it? As in a torque number?
The up & down movement sounds more like a bearing-adjustment issue.
05-20-09, 02:03 PM
"tight" is a relative term that involves the fixed cup not unscrewing whilst riding (which it did previously). I'm sure that, could I get proper access to it, it wouldn't be even close to tight, but it was tightened to it's current state by a set of channel locks and a lot of praying.
05-20-09, 02:25 PM
You do have to take the crank off to do this right. Then you have to take the bottom bracket apart. And you have to make the fixed cup tight, TIGHT, TIGHT! I would use a three-foot lever to make sure it's tight enough. I'm not kidding.
Hurry up and do this, because riding on a loose bottom bracket will damage it.
05-20-09, 02:29 PM
Thanks Tom. I'm not riding on it - I've taken it maybe two or three miles just to test ride it. No damage from me, but if it is damaged, it's probably the previous owner who was completely absurd...
05-20-09, 02:41 PM
Is it left handed or right handed thread? If it's right, which is wrong, I would use a little removable locktite. If it's left, I would start to investigate the deeper into the bottom bracket.
05-20-09, 02:48 PM
I'm pretty sure Peugeots of that vintage had standard French-threaded bottom brackets. That means the fixed cup is right-hand threaded, i.e. turn clockwise to tighten. With this thread, there is a tendency for the cup to loosen. This is why the world has pretty much standardized on left-hand threaded fixed cups. It's also why you have to make the cup so darned tight. Thorlak's suggestion of removable Loctite is a good one.
I just looked at their threadlocker page (http://www.loctiteproducts.com/products/subcategory.asp?CatID=10&SubID=48). It says that blue just prevents things from vibrating loose, so that might not be strong enough. It says that red is removable with heat, so maybe this is the stuff I remember that is very hard to take off, even when you try. Is that too strong? I'm confused. I haven't used Loctite in a long time.
05-20-09, 02:48 PM
It's right handed (threads clockwise, if you're looking at the front of the chainrings)
05-20-09, 03:09 PM
I was just suggesting the blue because the red is very strong and you want to be sure you know what you want before using it. loctite does have other locking options as well.
05-20-09, 03:45 PM
A little blue Loctite is fine. The primary locking force comes from the stretched threads that's been tightened to the proper torque. A two-foot breaker-bar for sure, a 1-meter one would be even better.
Loctite needs greaseless threads to work so an extensive cleaning ahead of time is in order. Also only put it on 2-4 thread widths on the last threads to engage on the cup. Not the first threads to engage
or on the BB. This way you limit the amount of loctite to a suitable area. Blue or equivalent is best.
The stronger ones can be a real hassle to remove if smeared over most of a fine thread BB cup. Heat
works to remove but they mean 350-450F, not exactly paint friendly.
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