Sunday, October 9, 2011

Repacking Bearings

Older bikes often have dried up bearing grease. Replacing dry or dirty grease will greatly prolong the life of your components. Marine bearing grease is cheap at an auto parts store, and will protect the bearings from water intrusion. Replace any damaged ball bearings. If you don't have the tools, at least try to get some oil in the bearings on a very old bike to protect from damage.


Hub Bearings:

  • Wheel bearing work requires cone wrenches and adjustable wrenches. Put the right size cone wrench on the inside bearing cone, and an adjustable wrench on the outer locknut. Unscrew the locknut, using the cone wrench to keep the axle from turning.
  •  Next unscrew the cone wrench, placing the wheel over an old towel or rag to catch the dirty bearings. Remove the axle, and gently pry out the balls using a small flat screwdriver.
  • Wipe all bearings clean, using degreaser when necessary (don’t use simple green on aluminum parts). When all surfaces (hub, balls, axle cones) are clean, fill each side of the hub with fresh grease.
  •  Place the ball bearings into the grease (typically 10 per side on the front, 9 per side in the back). Carefully place the axle back inside on the correct side, and then screw on the other hub cone. Replace the remaining washers and locknut, and then tighten the locknut against the cone. Adjust the bearings so that they spin smoothly and there is no play in the wheel.

Bottom Bracket Bearings:

 The bottom bracket is the bearing assembly which allows the cranks to rotate.
  • 3 piece bottom brackets require a crank puller (for cotterless cranks), lock ring tool, and a large adjustable wrench. First remove the cranks by unscrewing the crank bolts, then screwing the crank puller all the way into the crank and turning the lever until it pops off. 
  • For very old cranks with cotter pins, unscrew the nut holding the cotter on a little bit, then use a vice or large C clamp to press the pin out from the threaded side. You will need a brace for the other side of the pin (a block of wood with a hole drilled for the pin should work, or a 3/8” socket that’s bigger than the nut).
  • Remove the lock ring on the left side cup, then unscrew the cup. This is threaded normally. Remove the spindle and then unscrew the drive side cup using the 2 wrench flats. This piece is reverse threaded, and may require considerable force to remove (the right side cup can remain in place if removal is difficult; just clean it from the inside of the frame).
  • Clean all ball bearings along with the cups and spindle. Clean out the threads in the frame if necessary.
  • Repack the drive side cup with lots of grease and pack it full of ball bearings (there should be 11 per side, 1/4” size). Grease the threads on the cup and screw it back into the frame.
  • Pack the left side cup with grease and ball bearings, and then reinsert the spindle into the shell. Carefully screw the left side cup around the spindle to avoid disturbing the ball bearings.
  • Leave some play in the left cup. Tighten down the right side cup hard once the spindle and bearings are secure. Finish screwing the left cup in.
  • Secure the bearing adjustment with the lock ring. There should be no binding nor play in the spindle. A minor amount of drag is acceptable.
  • Bolt the cranks back on with lots of force on the crank bolts. If using cottered cranks, use the vice to drive the pins back in, and screw the nuts back on. The nuts will only hold the pins in place, not tighten the pins.

Headsets: 
  1. Older bikes typically have threaded headsets. This is the bearing assembly that allows your handlebars to rotate. First remove the stem and the top nut, as well as any spacers, washers, or brake cable stops.
  2. Unscrew the top bearing race over an old towel so that the bearings can’t get lost as they fall out. Once the race is unscrewed, carefully slide out the fork (the front brake cable may have to be disconnected).
  3. Clean all bearing surfaces, and put any loose ball bearings back into their retainers. Pack the top and bottom frame cups with grease, and replace the ball retainers.
  4. Slide the fork back in, then screw on the top race. If your headset chronically loosens, adding blue loctite on the fork’s threads may help.
  5. Replace all washers in the original order and screw on the top nut. Adjust the bearing race for minimal play, and then tighten the nut. Check for tightness/play, and adjust accordingly.
  6. Replace the stem and reconnect the brake.
  • Threadless headsets use a clamp on stem rather then a threaded locknut to secure the headset. This system is more secure and easier to service.
  1. First unbolt the top cap, and then unscrew the bolts holding the stem to the fork.
  2. Remove any spacers and slide the fork out. The bearing surfaces themselves are similar to the threaded headsets, so clean them and repack with grease.
  3. Carefully replace the fork once the bearings are secure, then add the spacers and stem. Screw on the top cap.
  4. The top cap controls the preload on the bearings. It does not need to be tightened very hard and it isn’t a structural part of the bike once the stem bolts are tightened. Simply screw in the top cap until play is eliminated, then align the stem and tighten down the stem bolts.

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