One-Piece Bottom Bracket Service
Typical Tools and Supplies
- Repair Stand, holds bike secure for easy work.
- HHP-2 bearing press (for installing cups only)
- HCW-7, (30 and 32mm common) or large adjustable wrench
- Grease PPL-1 Polylube® 1000
This article will discuss service on one-piece crank bottom bracket bearings("Ashtabula").It will also discuss pressing the three-piece cartridge bearings into the Ashtabula bottom bracket shell.
The one-piece bottom bracket and the one-piece bottom bracket shell are found on some older Schwinn® bicycles, many juvenile and 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. This crank also acts as the bottom bracket bearing axle.
The one-piece crank system can be replaced with a three-piece bottom bracket system, using a different bearing system and a spindle that is separate from the cranks.
One-Piece Bottom Brackets
The crankarm is threaded in the middle, and acts as the bottom brackets spindle. The crank drive side threading is a right-hand threading, and the non-drive side (left side) is a left-hand threading. It is necessary to first remove the left side pedal in order to remove the crank. Turn the left pedal axle clockwise to remove. See Pedal Removal for more detail.
- Locknut is left hand thread on one-piece cranks. Loosen left side locknut clockwise using the HCW-7, or large adjustable wrench. Use opposite arm for leverage.
- Remove washer. Note washer has keyed tab that aligns in slot along the thread.
- Remove adjusting cone clockwise with SPA-4 spanner.
- Pull both left right bearing retainers out of cups. Arm will not remove with bearing in place.
- Slide arm out of bottom bracket shell.
- Inspect drive side cone for wear. It is not necessary to remove cone for cleaning. If replacing, clamp arm in vise with right side cone facing up. Remove drive side cone counter-clockwise.
- Clean and inspect parts. Inspect bearing cups in frame.
Generally, if the bottom bracket is overhaul, there is no reason to remove the cups. If the cups are worn, or if the bottom bracket is being replaced, the cups must be removed. Use a punch and hammer to remove the cups. Tap on alternate sides until cup is removed.
Assembly and Adjustment
Most one-piece bottom brackets use a bearing retainers. Check the orientation of the retainers before installing as retainers have only one correct orientation. Inspect the metal cage that retains the ball bearings. The cage traps each ball with a hook. Look for the open side of the ball retaining hook. This open side of the cage should face the cone shaped race, not the cup shaped race. If in doubt, install the cage, and place the race inside and turn. If the cage is correct, it will feel smooth. If the cage is upside down, the cage retainer will rub on the race and it will feel different. Reverse the cage and test again.
Cut away of ball cage retainer and bearing cone
The procedure to assemble the bottom bracket:
- If the cups were removed, begin by installing cups. Use the HHP-2.
- Install drive side cone, if necessary. A thread locker is recommend.
- Pack bearings fully with grease.
- Place one bearing retainer on drive side cone. Inspect metal retainer. Large opening Ball bearings face cone, retainer side sits in cup.
- With bearing on cone, feed arm into bottom bracket and through shell. Install non-drive side bearing, and thread on adjusting cone. Adjusting cone is a left-hand thread, turn counter-clockwise to intall.
- Install keyed washer and locknut.
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. If bottom bracket is correctly adjusted, but bottom bracket grinds when spun, cups and or cones are worn and should be replaced.
- Begin with locknut loose. Turn adjusting cone counter-clockwise until it hits the ball bearing, then turn back clockwise to loosen 1/4 turn.
- Secure locknut
- Grab end of crankarms and rock sideways to check for play. If play is present, loosen locknut and turn adjusting cone counter-clockwise slightly to tighten. Re-secure locknut and check again.
- Repeat process of checking for play and re-tightening cone a slight amount until no play is felt. NOTE: The one-piece crank systems do not use a polished bearing system. There will be some roughness to a correctly adjusted bottom bracket. Adjust as loose as possible but without play in the bearings.