The bottom bracket is the assembly that the crank set attaches to.  The bottom bracket consists of a couple of bearing cups that screw into the bottom bracket cavity, a couple of sets of bearings, a spindle that turns on the bearings, two bolts or hex nuts that hold the cranks in place on the spindle and a lock nut that keeps the adjustable cup from going out of adjustment when the bicycle is being ridden.  The assembly might also include a plastic sleeve designed to keep debris away from the bearings.

Bottom brackets and their cavities, are more difficult to work on than seat post cavities, simply because special tools are required, to do the job.  Needless to say, grease will be required and I like to use a good quality synthetic grease, but that is just me.  Any quality water proof bearing grease will do the job.  The tool list itself includes: one 12" adjustable wrench with sharp jaws, a grease applicator, a ring wrench, an assortment of metal brushes, a small magnet, and a big bolt.  A good supply of cleaning rags will be worth having on hand also.

The bottom bracket's non-drive side should be loosened off first.  A ring wrench is required to remove the lock nut.  Other tools will do the job, but not without also doing damage to the component.  In this case, the Stronglight French threaded bottom bracket is valuable.  Care must be taken to ensure that it is not damaged, during removal and installation.

Even the correct tool will have a tendency to slip off of the lock nut.  Wear gloves and try to hole the business end of the wrench in place.  Once the lock nut is loosened off, it can be removed completely, for the time being.  Next, use the appropriate tool to loosen off and remove the non-drive side bearing cup.  Be prepared to catch the loose ball bearings that just might fall out.

Removing the drive side bearing cup can be very difficult.  If the cup was installed with no lubricant applied to the threads, then chances are the cup will be seized into place.  The drive side cup can be either right or left hand thread.  It is difficult to determine which, before trying to loosen things off.  You will need a good wrench that fits the cup well.

Though there are correctly sized wrenches, for each manufacturers bearing cup, I use a 12" adjustable wrench that is dedicated to this job only.  Dedicated because the jaws on the wrench must have a good sharp, or crisp, edges.  Rounded wrench edges WILL cause the wrench to slip off of the bearing cup, possibly doing damage to the cup, the frame and/or your hand.  Though the Peugeot's drive side cup unscrewed with little difficulty, I recommend holding the wrench in place with the Big Bolt, mentioned in the tools list.  The Big Bolt, snugged-up a tight "finger tight" against the adjustable wrench, will help keep the wrench from slipping off.  I recommend using the Big Bolt every time you attempt to remove a drive side bearing cup.  And, since the possibility of slipping exists during assembly, one might as well use the Big Bolt then also.

With the bottom bracket removed, you can begin to get an understanding of the horrors that this humble cavity contains.  Horrors that will impede ride performance, as well as component durability.  Many of these horrors get in through the open and exposed top end of an Old School seat post.  On one occasion, when the bottom bracket was removed, exposing the housing contents, the skeleton of a dead (obviously) mouse greeted me.  I often times see plastic bags, compressed into a balls, and jammed into the seat post top openings.  The plastic, of course, acts as a bit of a seal against foreign bodies entering the cavity and falling into the bottom bracket housing.

Of course, unwanted items and liquids can enter through another opening.  The space between the bearing cups and the crank spindle can, and will, allow water relatively easy access to this key apparatus.  Water that, sooner or later and more often than not, will cause oxidation - rust!  The only way to combat this kind of potential contamination is with a proper maintenance schedule.  I check bottom brackets and refresh lubricant on my personal bicycles at least once every riding season..

The Peugeot's cavity did not contain the horrors that commonly present themselves, however; the assembly itself was very poorly built.  To suggest that a craftsman built this bicycle would be foolish.  Look into the opening and see how far the frame's down tube extends past the point where it is doing any good what-so-ever.  This huge assembly flaw can and does interfere with the insertion of some bottom brackets.  This situation also suggests that such sloppy workmanship is probably present elsewhere in the frame set.  And the PR 10 was one of Peugeot's better bicycles back in the mid seventies.

But the too long tube will go unaddressed for now.  The present bottom bracket does fit just fine and, as so many people believe, "if it ain't broke, don't fix it".

Once the bottom bracket assembly is removed, begin by cleaning the bottom bracket housing cavity thoroughly.  Remove as much of the old lubricant and loose crud possible with a soft scraper.  Follow that with a good brushing with a soft wire brush.  I use a small brass brush or a seriously worn stainless steel one to complete this aspect of the task.

Wipe, or blow, out the loosened debris and do it again, until all loose material has been removed.  If you do feel the need to stick you fingers into this cavity, and you will feel the need, be CAREFUL.  The are most likely sharp edges in there and rust to boot.

Once satisfied the cavity is as clean as you can get it, try threading each bearing cup into its appropriate fit.  Ensure that each threads in and out smoothly.  If the do not thread smoothly, clean the cavity threads again and do the same for the threads on the offending cup(s).  Try again, until they thread in properly.

With everything going in and out the way they should, the last thing to do to prepare the bottom bracket housing, is to smear a thin coating of grease over the entire inside.  Ensure that all threads are coated.  This task is best accomplished with my fingers, but if you want to use your fingers, go right ahead.  Just remember to be careful.  During your cleaning, you might have missed smoothing out a sharp edge or two.  The purpose of this thin layer of grease is twofold.  First, the grease protects against the formation of rust.  Second, the lubricant does just that - lubricates fragile threads and helps with bearing cup insertions.

That's about it for bottom bracket housing preparation.  You could, of course, take the frame set to a local bike shop and have them chase the threads and face the ends of the bottom bracket lug.  Then you would be absolutely sure that your bearings are going to run as true as possible.  In fact, if you are seeking the best ride, you should do this sort of thing.  Every little improvement adds up invisibly to create an increasingly better ride.