The oil filters are being used for keeping away teh contaminater dirty oil and teh particles, which come into being due to the abrasion while the engine runs, from the engine and the transmission. The carbon particles, dust and dirty may mix into the oil while the engine runs. One port of these foreign substances deposit on the carter case, held by the oil filter and the plug magnet. While the smaller particles are being avoided without having being mixed into the lubricating system by having being filtered and so they do not damage the system.