ABSTRACT
In most simple crankcase-scavenged two-stroke engine designs, lubrication is carried out on a once-through-the-engine, total-loss basis. After lubricating the crankshaft bearings, connecting rod bearings, and piston-ring-liner interfaces, much of the lubricant burns in the combustion process and, burned or unburned, has to be removed through the exhaust system. Piston weight influences friction, and the losses due to friction between the cylinder walls and the piston skirt are more pronounced. Compared with the four-stroke cycle engine, the two-stroke engine is more susceptible to deposit formation in ports and the exhaust, formation of ash-containing deposits in the combustion chamber, piston wear, and corrosion. A true measurement of friction in a firing engine can only be obtained by subtracting the brake power from the indicated power, determined from accurate measurements of cylinder pressure throughout the cycle. The most commonly used method for evaluating friction power is the direct motoring test.
