My 1993 1.6L MX-5 with 103.000 Km was starting to make a faint ticking sound, coming from near the Cam Angle Sensor (CAS).
Since the car was due a timing belt and water pump change, I decided to go a bit deeper and pull all the hydraulic lifters to clean them.
From all the 16 lifters, only one was diferent from the others, and had some sort of burned in residue, even after cleaning it. To my surprise, it was the one closest to the CAS (rear of engine, intake side). Coincidence?
Here are pictures of a clean lifter, and the one with the residue: https://imgur.com/a/nN6VfUn
What could have caused this? Could this be the source of the ticking? Should I replace the lifter?