The thing is with Camshaft, Cranks, Chains, Cogs etc etc and any other solid mechanical timed mechanisms, if they fail in anyway, the issue is not intermittent. They all cause major and even catastrophic failures that would abruptly bring the engine to a halt. Or at best, the ignition of the Fuel would be compromised and result in a smoky cylinder or two or more. From my own experience, here are a list of things I found over the years. Maybe it might help someone one day.
Broken lug on Camshaft = ruff running through out rev range. Smoking engine. Continual clacking noise that increases f