Abstract: An engine has a housing and a working member movable within an interior of the housing and separating a combustion chamber from a non-combustion chamber. Additionally, the engine may include a chamber-ventilation system that may include a passageway with a first end of the passageway connected to the non-combustion chamber and a second end of the passageway located downstream of the first end of the passageway. The chamber-ventilation system may further include a filter system disposed within the passageway. The filter system may include a filter housing and a filter disposed in the filter housing. Additionally, the chamber-ventilation system may be configured such that, during operation of the engine, gas travels from the non-combustion chamber, into the first end of the passageway, through the passageway, to the second end of the passageway.