The master link is the one special link that lets a drive chain be opened and closed, or joined into a loop. It has a removable plate and two pins. All other links are riveted and cannot be opened by hand.
What it does
It joins the two ends of the chain into a loop. There are three kinds. A clip type has a spring clip over the pin ends. A press-fit type has a plate that is pushed over the pins and held by friction. A rivet type has pin ends that are riveted over with a special tool. An endless chain has no master link at all and has to be cut with a chain breaker.
Signs it is worn or failing
- The clip is missing, loose or bent. A chain that loses its clip can come apart.
- A joining link that looks different from the rest (wider, tight, or with a bright new plate) and runs stiff.
- A tight spot every time the link goes around the sprockets, which also shows as tight spots in the chain.
- A broken chain, chain snapped. The course warns that a chain that breaks can throw an end through the crankcase.
When to replace it
Fit a new master link every time the chain is joined, and with every new chain. Keep the old clip in the tool kit on the bike as a spare. If the chain has stretched so far that you have to remove links to adjust it, the chain is well beyond worn out and should be replaced with the sprockets, not shortened. See Check the chain for wear.
What to match when buying
- Chain size and type. Match the pitch (for example 428, 520, 525, 530) and the width. A heavier chain is not always wider, but the master link must match your chain.
- Plain, O-ring or X-ring type: the master link must be suited to the seal type.
- Clip, press-fit or rivet: buy the right one for the tool you have.
Fitting notes
- Fit the clip with its closed end pointing in the direction the chain travels, so the clip is less likely to catch and come off.
- Large chains (530 and bigger) can be a tight fit. A chain press or a pair of suitable pliers helps to push the plate on.
- Rivet links need a chain riveter, or careful peening of the pin ends over a solid support.
- See Join a chain with a clip, press-fit or rivet link and Identify the size of a drive chain.