Check the entire intake system for leaks. Here is a quote from a Lycoming engine flyer:
"Dust or some form of dirt is frequently the principle factor in premature piston ring and cylinder wear. If a worn or poorly fitting air filter allows as much as a tablespoon of abrasive material into the cylinders, it will cause wear to the extent that an overhaul will be required."
Univair supplies a wide variety of air filters for light planes. Protect yourself and your engine by replacing your air filter regularly.