Curious as to what internal engine condition (if any) has prompted this discussion. When and what condition was found. I am assuming nothing was unusual with a good running engine. It seems to me that a little dust or dirt drawn in on the intake stroke would just be blown out on the exhaust stroke. It appears that most if not all filters were added to running engines - what is the reasoning? Suspected cylinder wall erosion? I don't think these filters will add to the longevity of the bottom end of the engine.
John
John