Almost all H-D engines that vent the crankcase through the cylinder heads also expel oil through the same passages. Venting directly into the air cleaner, especially a free-flowing air cleaner, often results in an oily mess on the side of the bike. The Bluegrass Breather kit is a simple yet effective way to keep the oil inside the engine or at least keep it contained.; Simple yet effective way to keep the oil inside the engine or at least contained Banjo fittings and chrome tubes route the vented gasses upward so gravity can keep any expelled oil in the engine Recommend venting the crankcase to the open air by hiding the vent line up and out of sight beneath the tank Optional catch can 401-722 is available for those who would rather vent to a closed container