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Saturday, April 25, 2009

Adjustable Bottom Brackets

Performing maintenance/changing the grease and ball bearings on a bottom bracket is one of the most difficult things to do for a bicycle mechanic. You will need all the proper tools before attempting this, and its recommended you watch someone else with experience do it first.


Adjustable Cup - A cup containing ball bearings that screws into the left side of the bottom bracket shell.

Ball Bearings - Tiny metal balls used as rollers for the axle so it turns smoothly. Its recommended you use as many ball bearings as possibly, but leave a small gap the width of 1 or 2 ball bearings so they roll very smoothly.

Bottom Bracket (BB) - The bearings and bearing assembly which allows the bicycle's crankshaft to rotate.

Bottom Bracket Shell - The horizontal tube (1.5" x 3" long) at the bottom of the bicycle frame.

Cone - The piece which fits on top of where the ball bearings rest, along with grease. There are two cones and two sets of ball bearings in a bottom bracket.

Cup - The surface which holds the ball bearings, along with grease. The cup threads into the BB shell.

Fixed Cup - A ball bearing cup on the right side of the BB shell, in a fixed location (no adjustments). Fixed cups have built in pieces that fit right up against the surface of the BB shell.

Grease - You will want to fill the area with the ball bearings with bicycle grease to hold them in place and allow them to turn smoothly. Lack of grease will result in pitting the surfaces and end up ruining your bottom bracket. Use excess grease to keep the rust off.

Lockring - A round locking ring with outer notches which holds the bottom bracket in place. You will need a lockring wrench to properly loosen/tighten the lockring. (If you don't have a lockring wrench you will need to find a bicycle mechanic to do it for you.)

Race - The tiny surface inside the cone and cup which the ball bearings rest or rub against.

Retainer - A set of ball bearings held together with a round metal piece. Retainers are for amateurs. Professionals prefer to have loose ball bearings and lots of grease for extra smooth movement.

Seal Mechanism - A rubber piece that seals the spindle gap.

Spindle - Also called an axle or crankshaft, a metal rod which rotates inside a well-greased bottom bracket.


If you have good grease...

Depending on the weather conditions you should do maintenance every 2000 miles. If its really wet where you live (or you're leaving your bike out in the rain) you should do maintenance every 750 to 1000 miles. Remember parts rust even if you don't ride your bike.

If you're not keeping track of mileage, you will know its time for maintenance when your bottom bracket becomes sluggish, too loose, makes noticeable noises, is jerky, makes a constant clicking sound when rotated. Sometimes a part may just be loose, or it may be time for an overhaul.

If you have bad grease or if its a new bike...

You should clean it out ASAP (within the first 1000 miles) and replace the grease and ball bearings.

NOTE: Grease injection systems and water tight seals (they lessen the water, they never full protect it) do not prevent the need for maintenance.


Once you know all the parts and have all the tools, you just need to remove the parts, place them in order, clean out the old grease, toss out the old ball bearings, check for pitting (you may need to replace your bottom bracket), add lots of new grease (pack it in there), add ball bearings (make sure the size is the same using a gauge) to the grease (almost fill it, replace the cone inside the cup, place the parts back inside the bottom bracket in the reverse order that you removed them... test and enjoy.


Don't pay too much for your ball bearings. Some places overcharge you for ball bearings. A bag of 100+ ball bearings should cost you $2 to $5.

Don't worry about ball bearings that fall on the floor. They're cheap and cost less than a penny. You shouldn't use them either because they collect dirt off the floor easily, which will cause pitting inside your bottom bracket and wear it out faster.

Don't be afraid to get your hands dirty packing the grease in. The more grease the better.

To be continued...

1 comment:

  1. Here is another tip. You get what you pay for. You may save a bit on cheap ball bearings, but only until they rust or dent, and damage your bearing cups. Go with high quality stainless steel. Do it right the first time.



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