quote:
Originally posted by 1sttruck:
A mechanic on one aircraft site observed that MMO seemed to work by allowing valves to keep from sticking with heavier deposits, as opposed to removing all of the deposits from around the valves. This suggests increased lubrication, which I guess isn't surprising as it's often described as an upper cylinder lube. If the valves move more freely they'll need less force to actuate, so they might be quieter too. If they actuate more freely with hydraulic lifters they might be providing slightly better flow and slihtly better valve timing too. If this is the case one would expect to see less improvements, maybe noise excepted, with solid lifters.