There are a number of reasons why your adhesive may not be curing properly:

• First ensure that you have the right instructions for the exact formulation that you are using
• Check cure times for the particular substrates that you’re using
• There may be a coating on the metal substrates preventing activation of the adhesive – you may need to remove this before applying the threadlocker
• If you are already using a high viscosity threadlocker, then the gap may simply be too big
• The surface area exposed to air is too large
• The substrates are not suitable for threadlockers which are activated by contact with metal