Bicycles/Maintenance and Repair/Chain Rings

A two-ring assembly. Notice the bolts with slotted nuts that fasten the chain rings to the spider of the crank, and the crank arm extending upward. When a guard plate is installed (not shown), it is spaced from the largest ring to allow clearance for the chain.

Two types of chain ring bolt. The silver bolt has a slotted nut for use with a chain ring nut wrench, and has no hex recess. The black bolt uses hex wrenches for both the screw and nut, 5mm and 6mm respectively.

At times, for cleaning or to change the chain rings themselves, the rings must be removed. This is simply done and in nearly every case, need not affect the crank arms themselves, or the bottom bracket.

Terminology

• Chain Rings. These are the cogs (sprockets) that are located near the pedals. There is always at least one sprocket and sometimes as many as four (see Thun quad chainring with 24t, 30t, 38t and 46t. Three sets of sprockets are common on geared bicycles and four sets are rare. The sprockets are bolted together or riveted onto the spider of the crank to form the chain ring set.
• Chain Ring Bolts. These fasten the chain rings together, and fix the assembly to the spider of the crank. They exist in different lengths depending on their purpose, and can be made of steel or softer alloys.
• Crank Arms. The crank arms are the long parts that join the pedals to the main shaft in the bottom bracket of the bike. On the right side of the bike the crank arm extends into a spider shaped plate.
• Spiders. The spider is an extension of the right crank arm, that the chain rings bolt onto. It has either a four or five bolt pattern, depending on the design.
• Pedals. These are screwed onto each crank arm. The left pedal's attachment has a left-hand thread while the right pedal has a more normal right-hand thread.
• Chain Ring Guard. A metal or plastic part that protects against damage from the rotation of the outside chain ring.
• Chain Ring Nut Wrench. A special wrench, sometimes used to assist with chain ring bolts. It is made to fit the slotted nuts of these fastenings, though is not always needed.
• Pedal Wrench. A wrench sized to fit the nuts for pedal removal.

Removal of Pedals

It is a fact that most chain rings and guards cannot fit over the pedals of the bike, so if the intention is to completely remove them, the pedals must first be unscrewed.

• Use a pedal wrench or a conventional 15mm wrench to UNSCREW THE RIGHT PEDAL ANTI-CLOCKWISE, while holding the work firmly to avoid its moving. The pedal is installed with a torque of about 360 in-lbs, (30 ft-lbs, 40.7 N.m), and this point should be noted during its replacement.
• Although this procedure does not require the removal of the left pedal, it is done by UNSCREWING THE LEFT PEDAL CLOCKWISE, and REPLACING IT BY SCREWING ANTICLOCKWISE, since it has a left-hand thread.

Remove or Slip the Chain

The removal of chain rings is best done with the chain completely removed though it is not strictly necessary for bolt replacement or other slight work. Remove the chain by breaking the master link, or just derail it toward the inside of the bike at the chain rings while moving the pedal slightly, depending upon the situation. While derailing the chain, it helps to move the rear detailleur cage inward to slacken the chain.

Removal of Rings

Some rings can be removed then replaced in any position, but some others need to have their alignment considered. This alignment requirement is more likely for multiple chain ring sets. The chain rings themselves often bear a mark to denote their intended top positions, but in case they do not, it is a good idea to add a mark to the top of the rings with a marker pen or other method to keep things clear.

The screws and nuts of chain ring fastenings are made with recessed allen key heads (hex wrench), and at times the nuts might be slotted instead. They can be made of steel or a softer alloy. Steel screws are likely to maintain higher torques than alloy, and the makers recommended torque settings will reflect this. A common fitting is a 5mm hex for the screws and a 6mm hex for their nuts. Because the tension on the bolts is fairly high, at least one long-shank hex key is preferred.

For single rings it will always be possible to turn the crank so that both sides of the screws are accessible with two hex wrenches, but in any case working only from the front will usually work for removal. For multiple rings, if there is a difficult thread, there might not be space to get to the nuts with a hex wrench. In this case, slotted nuts come into their own. The chain ring nut wrench has a slim profile that allows it to fit between rings and still engage the slots in the nuts.

For multiple rings the procedure is much the same, starting with the outside bolts, removing the guard and whichever rings as necessary to reveal the next layer of bolts, and so on.

Slide the chain ring guard and the various rings over the crank with the pedal removed.

Installing the Rings

Grease or oil the bolts before assembling the rings again, and pay particular attention to the torque that is recommended for the ring bolts. Additionally, do not apply full torque to any one bolt in a set on its own, but rather bring up to torque the whole set together, a little at a time, to avoid any distortions. A set here means, the grouping of bolts in the same plane; the inner set, the outer set etc., should they exist.

If the manufacturer's data is not available, then refer to torque tables such as Park Tool: Torque Specifications and Concepts for suitable values to use.

Attach the pedals to the crank arms, and re-connect the chain.

Few riders are lucky enough to own expensive torque wrenches for their bikes, so it might be as well to get the assistance of the bike shop for work that requires their use. That said, many are known to approximate the necessary torques by judging the force applied to a wrench lever of known length. That is to say, torque is just the product of force and length. For example, a 30 ft.lb torque is applied when a thirty pound force is applied at right angles to the end of a one foot wrench. The accuracy of this method is as good as the user's ingenuity at judging or measuring the applied force. Formulas for converting to other torque designations include: in.lb = ft.lb x 12 in.lb = Nm x 8.851 in.lb = kgf.cm / 1.15

Technical Note:

Afterthoughts

It has been brought to the author's attention that the hanger bolt that fixes the hanger of a rear derailleur to the frame is very similar to a chain ring bolt, and in an emergency might solve a problem.

See Also

• Gearing Calculations  : A Wikibooks page. Contains much data on gearing dimensions and examples of calculations.
• Torque Specifications and Concepts  : A Park Tool page. Contains tables of specific torque values for the parts of the bicycle.