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Repair Help and Education

Adjustable Type Bottom Bracket Service

Useful Tools and Supplies

This article will discuss the service of adjusting bottom bracket bearings. It will also review the types of tools required. The basic concept for bearing adjustments is to get the bearings adjusted as loose as possible but without play. This can be done by purposely beginning with play in the adjustment, and then tightening in small increments until play is gone. With much use, the bottom bracket bearings, cups and cones may become worn and pitted. In this case, a smooth bearing adjustment will not be possible. The bottom bracket will need a complete overhaul and most likely new parts as well.

There are three common types of bottom brackets.

 

 

 

  1. Three piece bottom bracket- Cartridge type: Bikes made in the last few years tend to come with a "cartridge" bottom bracket. For the most part, these are unserviceable, and the entire unit is simply removed and replaced when they wear out. They can not be greased or adjusted before that time. Some brands use common industrial bearings, just like ones found in cars, pumps, electrical motors, etc. Generally, the bearings are intended to be used until they wear out. With most brands, the entire unit including the spindle is replaced. For service of cartridge bearing bottom brackets, see Cartridge bearing type bottom bracket service.
  2. Three piece bottom bracket- Adjustable type: These usually contain four major pieces: lockring, adjustable cup, spindle, and fixed cup. The left side lockring has notched rings, and the adjustable cup may have holes for a pin spanner, or notches for a wrench. The right side cup will have wrench flats, but no lockring. Cups may be removed and replaced separately, and the spindle may be replaced separately. A set of round ball bearings are found in each cup, typically eleven balls per side of 1/4-inch diameter. This type of bottom bracket may be cleaned, greased, and adjusted.

     


    An older adjustable type bottom bracket.
  3. One-piece or "Ashtabula" bottom brackets: These are found on some older Schwinns, juvenile bikes, some BMX bikes and on many department store-type bikes. One piece of steel forms the crankarms and goes from the pedal, through the bottom bracket, to the other pedal. See One-piece Crank Service for procedures.

 

Bearing Adjustment and "Feel"

Bearing surfaces are made from hardened steel. The surfaces are cut typically by grinding. Round ball bearings roll on the curved surface of the cup and cone. Even the highest quality bearing surfaces will have slight grinding marks. In the left image below is a high quality cone magnifed two hundred times. Notice the parallel marks from the grinding stone. Also note a slight pit from wear. The right hand image is a bearing magnified the same amount. It does show some surface marking, but is generally smoother than the cone or cup. Bearing surface smoothness will vary between manufacturers and between models. Some bearing system will simply "feel" smoother because they are smoother. This is why it is difficult to adjust by using a subjective feeling of smoothness. Generally, adjust bearings for the loosest setting that has no knocking or play, regardless of this relative smoothness.

Cone bearing surface

 

Ball bearing surface

 

There is a fairly simple test to detect a worn out bottom bracket bearing. Shift the chain to the inner most rear sprockets front and rear. Drop the chain off the smallest front ring, and arrange it so it will not strike the chainrings. Spin the crank while holding the frame. If you feel an obvious rumbling and/or grinding sensation resonating through the frame, the bearing surfaces are most likely worn out. Internal parts may be required. Typically, the spindle will wear out before the cups. The ball bearings tend to wear out last.

Check bearings

 

 

Adjustment Procedures

The adjustment procedures below assume the bottom bracket axle, cups and bearings are not badly worn. If a good adjustment cannot be found, it is likely the parts are wore out and need replacement. Trace the bearing path with a ball point pen.

When adjusting the bottom bracket, work in small increments. To help in this, begin by taking about two inches of tape and making marks on one edge every 1/8". Stick the tape on the left side of the bottom bracket shell so the marks face outward. These will be reference marks when adjusting the bearings and represent the small increments used when turning the adjustable cup.

Adjustable bottom bracket consist an axle and two cups, one on either side of the bike. The drive-side cup (right side) is sometimes refered to as the "fixed" cup because it is secured into the frame. Adjustments are made to the non-drive (left side) cup. If you did not assemble the bottom bracket yourself, it is recommended you check the security of the drive-side cup. A drive-side cup will not allow a proper adjustment. When overhauling and regreasing the bottom bracket, the drive-side cup can remain in place.

 

NOTE: If bottom bracket bearing surfaces are worn out, it will not be possible to have a smooth adjustment when play disappears. The bottom bracket parts will need replacement.

Badly worn race surface

 

 

Shimano® Dura-Ace and XTR Adjustable bottom brackets

These bottom brackets use a cup and cone type system. The bearing adjustment is from the left side, similar to other adjustable bottom brackets. The bottom bracket uses both a ball bearing and a needle bearing system on left and right side cups. When overhauling, it is recommended to leave the needle bearing and ball bearings in the cup. Clean by flushing with solvent.

Dura-Ace cup and axle

 

 

Dura-Ace

The non-drive side (left) of the Dura-Ace bottom bracket uses 20 internal splines in the cup. These tend to be shallow. When adjusting the Dura-Ace, use the BBT-22 or BBT-32 to adjust and hold the cup. Secure the lockring with the BBT-7 lockring spanner. Use care to hold the BBT-22 fully into splines of the cup. Note in image below the right crankarm is mounted. Use this as a lever when checking for play.

Adjust from left side

 

 

XTR

Adjustable type XTR BB-950 use the BBT-8 for both drive and non-drive cups. The lockring is the BBT-7, as seen in the image below. The procedures for service is similar to the procedure described above.

BBT-7 on XTR