Even the most careful cleaning and lubrication can never completely prevent wear in the drivetrain. It is time to replace parts at the latest when there is a clunk when changing gear. After two to four chain change intervals, depending on the degree of use, the chainrings and sprockets are also worn out. The chain jumps when shifting and has too much play between the teeth. Frequent model changes within a few years do not make it easy to procure spare parts. Our tip: Bring the dismantled crank with you when you go to a specialist dealer to buy new chainrings.
How to prepare the repair: Use an assembly stand. Remove the rear wheel to slacken the chain. Dismantle the chain if it is worn or lift it inwards off the chainrings. Then proceed step by step.
Remove crank
1 SRAM/Truvativ crank
These cranks can be recognised by the central retaining screw with integrated puller. Loosen the inner Allen screw until its head presses against the outer ring in the crank eyelet when unscrewing, thus lifting the crank off the axle.
2 Shimano Hollowtech II
Here, two Allen screws close a clamping slot. Loosen both screws alternately in half turns until they are loose in the thread. The clamping slot expands and the star screw in the crank eye becomes loose.
3 Loosen the star screw
Insert the star-shaped part of the tool (Shimano TL-FC16) into the recess of the screw ring in the crank eyelet. It pulls the crank flush onto the axle and is only screwed hand-tight.
4 Release the wedge lock
There is a small plastic plate in the now widened clamping slot that secures the crank against slipping on the axle shaft. Lever up the wedge from below at an angle to pull the crank off the shaft. Installation is carried out in reverse order.
Dismantle crank
1 Remove the right-hand crank
Release the axle shaft from its clamping fit in the bearing shells with a gentle blow. Then pull the shaft and right-hand crank out of the bottom bracket to the right.
2 Triple crank
If you have three chainrings, first remove the smallest chainring from the crank arm. The chainring is bolted directly to the crank from the inside with Allen screws. A protective ring is mounted on the outside of the largest chainring. It is attached to the largest blade with four screws and prevents the chain from falling off. Remove this ring as well.
Open 3 blade screws
Both large chainrings are held together by four Allen screws with slotted threaded sleeves. Shimano has been using T30 Torx screws for 10-speed drivetrains since 2011. A measured hammer blow on the L Allen key helps to loosen the bolt and sleeve from each other.
4 Sleeve and counterholder
The special Shimano TL-FC16 tool is required as a counter-holder for particularly tight screw sleeves. The spanner is also used to reliably lock the bolt/sleeve connection during assembly.
5 Clean sheets
The smallest chainring is often used very little and can continue to be used. Clean reusable chainrings with a little white spirit on a cloth.
6 Clean the axle shaft
Wipe the cranks and axle shaft clean and make sure that the rubber sealing ring of the left-hand crank is seated in its fitting.
7 Maintain bearing shells
Also wipe the inside of the bearing shells clean with a cloth. Apply a thin layer of grease to the contact surfaces before reassembly.
8 Grease blade screws
Clean the retaining screws and sleeves carefully. Apply a thin layer of grease to the threads to prevent corrosion.
9 Assembly aid
Prevent the screw sleeves from turning during assembly by holding them with your fingertips. Use the counterholder to finally tighten the screws.
10 Align sheets
Attention when assembling: The climbing aid rivets on the centre and large blade must point inwards towards the frame. The labelling on the large blade is on the outside opposite the crank. The inner blades each have a pin in the inner round. These must be positioned behind the crank. Otherwise the chain cannot climb safely. Finally, fit the trouser guard ring.
