1. If the safety ring is difficult to turn, slightly pull apart the two lips with circlip pliers.
 
2. If the safety ring turns too freely, remove it with a pair of circlip pliers, then tighten it back again using flat nose pliers and then readjust it on the assembly collar.

3. From time to time, put a drop of vaseline oil between the two collars.
 
4. If the blade opens too freely, it should be tightened back again. In order to do this, remove the safety ring (see step 2) then place the head of the rivet on a metal surface and rivet the other end by gently hitting it with a hammer until the right amount of tightening has been achieved.
Readjust the safety ring by tightening it again, if necessary, in order to obtain the desired level of functioning. (see step 2).

5. If the blade is difficult to open inspite of "le coup du savoyard" (knocking the end of the handle on the edge of the table), without doubt this is due to humidity; dry the knife on a radiator and lubricate the main joint with liquid wax or vaseline oil.
 
As a general rule, never leave the knife in a humid environment.