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Tham khảo tài liệu 'motorcycle mechanics 2009 part 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Single Lower Bild GENERAL THEORY All two-stroke or four-stroke motorcycle engines have one thing in common the crankshaft. They use this same basic device to convey the powerful energy released by burning gasoline and convert it into useful rotary motion. Combustion pressure literally turns the crank. The heart of every engine is its lower end the crankshaft and parts associated with it that convert linear motion into rotary motion. The crank has come a long way from the hoist used to raise a bucket of well water. In the modern motorcycle the crank operates at speeds measured in thousands of rpm it deals with forces measured in thousands of pounds and at temperatures in the hundreds of degrees. The lower end must have great strength and rigidity to handle these forces without bending or breaking. The crank assembly depends on highest quality bearings tightest fits and clearances and the best lubrication in the entire engine to do its job smoothly without rattling apart or burning up from friction. When we look at the engine as a cranking device the parts Fig. 12-1 function as follows. The piston is acted upon by the pressure of expanding gases in the combustion chamber. The piston is free to slide in the straight linear cylin der. The piston transmits its linear motion to the small end of the connecting rod through a pivot joint made up of the wristpin and the wristpin bearing. The other end of the connecting rod the big end has another pivot joint where the rod is connected to the crankshaft throw. The small end of the rod undergoes linear piston motion and the big end of the rod undergoes rotary crankshaft motion. The rod undergoes an angular combination of linear and rotary motion. The crankshaft receives angular pushes from the rod at the crankpin or rod bearing. The crankpin is rigidly mounted in two flywheels. The crankpin-flywheel assembly rotates on the main bearings and puts out useful rotary force torque through the main shaft. The crankshaft main .
