TAILIEUCHUNG - Motorcycle Mechanics 2009 Part 6

Tham khảo tài liệu 'motorcycle mechanics 2009 part 6', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | SUNBURST HEAD a Fig. 8-3 Four popular cylinder head features Valve d COMPRESSION RELEASE Straight Rail Fig. 8-4 Two-stroke piston ring types Fig. 8-5 Wrist pin is shown in sectioned piston Cross Section Keystone L Section or Dykes or Headland Fig. 8-6 Typical circlip or snap ring crankcase or lower end of the engine. This mixture is drawn in by the vacuum created underneath the piston as it travels up to the top of the bore. Atmospheric pressure forces a rapidly moving column of air through the carburetor where it picks up the fuel-oil mixture. The column of mixture then travels through an intake passage manifold to the intake port area located low on the cylinder barrel Fig. 8-7 . The opening and clos- 96 Unit 8 Port Opening Port Closing Two-Stroke Engine Upper End Rotary Valve. A rotary valve system controls the intake port by using a partially cutaway rotating disc to open and close the port at strategic times Fig. 8-11 . This design performs better generally than conventional piston porting. The carburetors are mounted on the sides of the engine to give more direct flow to the rotary valve Fig. 8-12 . The rotary valve cut allows the air-fuel-oil charge to enter the vacuum of the crankcase chamber during the entire or any desired portion of the upward stroke of the piston Fig. 8-13 . The crankcase then becomes an interim storage chamber for the fresh air-fuel-oil mixture. Oil in the mixture settles out onto the roller or the ball bearings on the crankshaft and connecting rod providing lubrication for these moving parts. It is generally desirable to make the crank chamber volume as small as possible to lessen the tendency for the mixture to compress in the crank- Fig. 8-11 Rotary valve disc Fig. 8-13 Rotary valve operation showing relation of valve to port on opening and closing case. A small chamber improves the flow of gas through the transfer ports to the combustion chamber because a small volume of gases is easier to move up the transfer ports than a large .

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