The following is an excellent series of photographs and instructions for working on the CX4 trigger group created by the Tactical Excellence company.
I would add the following comments.
1. The TE instructions begin by showing removal of the magazine adapter and the magazine release. This is good information but you do not need to touch these items if you are only working on the trigger housing.
2. The TE instructions then continue by showing removal of the bolt stop (the long L-shaped lever that pivots at the front of the trigger housing). Replacing the trigger spring back onto the bolt stop during re-assembly of the trigger is an absolute pain. Do not remove the bolt stop unless you absolutely have to do this. You must remove the bolt stop to remove the trigger itself but the bolt stop can be left in place if you are only working on the hammer. I will show how this is done later.
Tools you will need.
1. A medium sized screwdriver with a wide, flat, blade. You are going to use this item as a lever, not a screwdriver, so any broad, flat, piece of metal similar to a screwdriver will work.
2. A pin punch to push the trigger and hammer pivot pins out of position. If you buy our trigger upgrade the hex wrench supplied with the trigger is great for this job. The forces required to remove the pins are very light.
3. Small needle nosed pliers.
Special tools. These items are not required but you will find they make your life much easier.
1. An alignment pin slightly thinner than the hammer pivot pin and about 3/4 of an inch long. Use will be explained later.
2. What is known as a "spring hook" for positioning the hammer and trigger springs. These are available in various shapes and sizes commercially (eg McMaster Carr catalog or a really good hardware store). An excellent substitute is an appropriately shaped dental tool. You will sometimes see items like this sold at gun shows also.
Hints and Tips. Read before starting work.
During disassembly and reassembly of the CX4 it is important to put the hammer into the correct position for each stage of the process. Failure to do this can lead to broken spring guide rods and buffers.
1. Before the upper and lower halves of the firearm are taken apart the hammer of the CX4 must be cocked and the bolt moved to the closed position. First, remove the magazine. Next the action is checked to make sure that all cartridges have been removed and that the rifle is safe. The hammer is then cocked by use of the cocking lever. The bolt will move to the closed position automatically after cocking the hammer.
2. Prior to putting the upper and lower halves of the firearm back together the hammer of the CX4 must be cocked. If the trigger housing has been removed the hammer can be cocked before or after the trigger housing is put back into the lower half of the rifle. If the hammer is cocked before the trigger housing is put back into the lower half this helps to stop the hammer pivot pin accidentally falling out during assembly. If the hammer is cocked after the trigger housing is replaced in the lower half the cocking process requires less effort. In either event, the hammer is cocked by forcing it back and down until it locks in the cocked position. This can take quite a bit of effort so push down on the hammer firmly.
3. If you plan to disassemble the trigger group then the hammer will need to be released to the fired position to remove tension from the hammer spring before the trigger components are disassembled. It is easiest to release the hammer by pulling the trigger while the trigger housing is still in the lower half of the firearm after seperating the two halves. The trigger can be released with a little more effort after the trigger housing is removed from the lower half. In either case, control the hammer during de-cocking to prevent it moving forward in an uncontrolled manner.