This article is from the Bicycles FAQ, by Mike Iglesias with numerous contributions by others.
From: Jobst Brandt <firstname.lastname@example.org>
Date: Wed, 12 May 1999 15:38:14 PDT
The SACHS Power-link, can be separated easily alone but not when in a
chain. The link is designed not to open by axial compression alone,
typically when a new chain is used on worn sprockets, where skipping
over teeth can cause inertial compression by the trailing chain. To
prevent this occurrence, a recess around the head of the stepped pin
makes more than a half circle, preventing the pin from sliding in its
slot. That means the side plates of the link must be pressed
together, taking up side clearance, to raise the head of the sliding
pin above this retention.
To open the chain, find the link, make an upside down U-shape of the
chain with the link as the cross bar, the adjacent chain hanging down,
grasp the link diagonally with pliers across the the corners to which
the pins are fixed, not the corners with the keyhole slot. Pushing
the side plates together assists removal but is not essential, the
diagonal force having a lateral compressive component.
Before using a Power-link, put it together to see why it does not
readily slide from closed to open position. Road grit makes this even