Kuryakyn 9928 Crankcase Breather Kit This great looking Crankcase Breather keeps oil from being ejected into the air cleaner through the breather system. Excess oil now runs back down into the engine, rather than running into the air cleaner to be blown all over your bike. Note: NOT for use with stock Harley-Davidson&#174; air cleaners. Note: Kuryakyn part number: 9928.