Parts are much bigger on a Pratt and Whitney aircraft engine.
@Sun City, you have also had extensive training on the engine and you are familiar with the parts.
You will need a main spring vise to relieve the tension of the mainspring so the mainspring can be safely removed from the lock. A screwdriver isn't the only tool you will need.
Mainspring Vise, to safely compress a mainspring - Track of the Wolf
In the picture below,
@Erzulis boat is showing the tumbler with the bridle removed to show the fly. Its the little piece in the notch of the tumbler and the sear is resting on the fly. It has pushed the fly over the half **** notch and will ride over the notch and continue to rotate to strike the frizzen, make sparks and set off the charge in the pan
The half **** notch is just above the B in bevel. The nose of your sear is resting in the full **** notch. The bevel of the fly can also be seen and is facing the half **** notch when it should be facing the full **** and the nose of the sear.
Now that you,
@Sun City, have the lock out and the hammer in full ****, does the fly move easily in the notch in the tumbler? If the bridle screws are too tight, that may bind the fly in the notch in the tumbler. Back the sear screw out 1/4 to 1/2 turn. Does the fly move freely in the tumbler? Pull the hammer back slightly to get the nose of the sear out of the full **** notch. Lift the sear to allow the tumbler to begin to rotate past the nose of the sear and allow the nose of the sear to ride on the tumbler. The nose of the sear should push the fly forward to cover the half **** notch. Now the nose of the sear will ride on the fly and pass over the half **** notch. If the fly is installed backwards the nose of the sear will stop on the fly.
If you don't have the spring vise to take the lock apart, find a muzzle loading rifle gun smith to take the lock apart and install the fly correctly.