amount of oil being ckepwsited on the cylinder wali. The lower groove or grooves often have holesor slots in the bottom of the grooves to pemi ts oil drainage frum behind the rings. The piston lands are parts of piston between the ring grooves. ' Ihe lands provide a seating surface for the sides of piston rings main section of a piston is known as the skirts. It forms a bearing area in contact with the cylin The piston pinhole in the piston also serves as a bearing for the piston pin, which is used to connecT the conneeting rol. In addition, bx cause pistons operate under exceedingly difficult mechanical and thernal c onditions, piston must be strong enough to stand the force of the expansion, yet light enough to avoid excessive inertia forces when their direction of travel is reversed twice each revolution. Piston nust Ix able t withstand the heat from the buming air-fuel ixture, plus the heat gene rated by friction The connex ting rod is attached to the crankshaft at one end( big end )and to the piston at the other end( small CGas end).In operation, the connecting rod is subjected to both gas pressure and inertia loads, and therefore it must be ad quately strong and rigid and light in weight as well. The con- necting rod showT in Fig. 1-3 is in fonn of a bar with ring- shaped heads at its end. So they are generally fabricated from high quality steel are composed of connecting rod small end connecting md shank, connecting rod big end, connecting md cap, and connecting rod bearing half shells. Shank of the connecting rod is provided with an J-cross section to give the rmd maximum rigidity with the minimum of weight. The big end of the rod is split so that it can be connected to the Fig 1-3 A piston and a connecting-rod crankshaft. To avoid misplacing the rod caps during assem- 1.2-compression rings 3-oil rings 4"piston piston pin 6piston-pin ring bly, the connecting ruls and their mating caps are marked on -connecting rod ushing 8--connexting rod one side with serial numbers, starting with the first rod from -connecting rod llt 10-tonnecting rod nut 11. 12--crank bearing balf shells the radiator, to identify their location in the engine 13-ccnneeting rd eap Some connecting rods have an oil spurt hole in the yoke or at the cap-mating surface to provide cyl inder wall lubrication. The small end of the connecting rod is attached to the piston by a piston pin. In some cases the small end of the rod is clamped to the pin or has a bushing in it to allow the pin and rod oscillation. In other designs the pin is bolted to the rod. Connecting rod are usually drilled to provide h brication to the piston pin and also to spray oil into the bottom of the piston for piston cooling on some de The crankshaft, regarded as the backbone of the engine, serves to change the reciprocating mo- tion of the piston into rotary motion and handles the entire power output. The periodic gas and inertia forces taken by the crankshaft may cause it to suffer wear and bending and tensional strains. The crank- shaft therefore must be adequately strong and wear-resistant. So the crankshaft is either forged from a high ality steel or cast in a high-strong iron. The crankshafts shown in Fig. I-4 is actually mede up of vari