Automatic chain tensioner uses the oil in the primary as its own reservoir Has its own pump and operates like a hydraulic lifter in the engine Once you install it, there is no need to adjust the primary chain again Will hold up to engines over 100hp Maintains a constant zero lash between acceleration and deceleration No more chain slap inside expensive primary cases or excessive vibration Will work on 1965-E84 Big Twins (Shovelheads) if primary is converted to an oil bath type.