Changing a mortise lock latch

On a mortise lock, the curved side of the latch needs to meet the striker plate on the door jamb when the door is closed. However doors may be hinged on the left or right so the latch as supplied may not be suitable. It is fairly simple to reverse the latch in a mortise lock to suit any application.

1.	Release the screw holding the side plate on to the lock and lift off the side plate.
2.	The latch is normally held in place within the lock by a spring over a locator. If the door handle cam is positioned above the latch, lift it off and put it to one side - it will go back before the reversed latch is fitted (the cam is shown right *under* the latch).
3.	Using a small screwdriver push the locator against the spring towards the latch to unseat the locator. Remove the locator and spring. NOTE that care is needed to ensure that the spring does not fly off with the locator.
4.	Remove the latch from the lock and turn the latch over so that the curved side of the latch is reversed (i.e. if it was uppermost before, turn it over so that the curve is facing down or visa versa). The two orientations of the mortise lock latch are shown to the right. If the door handle cam was positioned under the latch (as shown above), lift it off - it will go back after the latch has been refitted.
5.	If the door handle cam was originally positioned above the latch, relocate it in the hole in the backplate of the lock - make sure that it is orientated to accept the latch. Position the spring and locator in the back of the latch and fit the latch into the lock in the required orientation. Using fingers, small pliers or similar, push the locator against the spring and re seat the locator.
6.	If the door handle cam is to be positioned above the latch (as shown here), relocate it in the hole in the backplate of the lock - make sure that it is positioned to operate the latch. Replace the side cover and secure with the screw. Before fitting the mortise lock to a door, check that the handle cam moves freely and that the lock is functioning - if the mechanism within the mortise lock is slightly miss-aligned, screwing the side plate onto the lock can cause it to become jammed.