Camshaft, Rocker Arms, Pushrods (Valve Train)

NAME: JAMES TSAI

Objective: -To learn about valve trains and its components.

-Alternatives to a pushrod system-Advantages/Disadvantages of SOHC and DOHC

What is a Valve Train?• What is a Valve Train?• Description: The valve train typic

ally includes the camshaft, valves, valve springs, retainers, rocker arms and shafts. On engines with traditional mounting of the camshaft in the cylinder block, the valve train also includes lifters and pushrods.

• Purpose: The cylinder head’s valves, when synchronized with the crankshaft of the cylinder block, allow the engine to “breathe”. In an engine, this means pulling the air and fuel mixture into the cylinder, then pushing the burned exhaust gases out. The better an engine breathes, the more efficient it becomes.

Which valve is intake, which is exhaust?

• - Just as the piston starts moving downward in the intake stroke, the intake valve would open. The intake valve would close right as the piston bottoms out.

• - The exhaust valve would open right as the piston bottoms out at the end of the combustion stroke, and would close as the piston completes the exhaust stroke.

What alternatives to a pushrod system exist?

• Inline -- the cylinders are arranged in a line in a single bank

• V -- the cylinders are arranged in two banks set at an angle to one another

• Flat (also known as horizontally opposed or a boxer) -- the cylinders are arranged in two banks on opposite sides of the engine

Advantages/Disadvantages of SOHC, DOHC

• Single Overhead Cam (SOHC) – the internal combustion engine design where one camshaft is located above the valves. SOHC engines are generally (but not always) limited to two valves per cylinder, one for intake and one for exhaust.

Advantages Disadvantages

-small in size -If the springs were not strong enough, the valves might come away from the rocker arms and snap back-reduced efficiency due to moving parts

• Double Overhead Cam (DOHC) – the internal combustion engine where the camshaft that operate the intake and exhaust valves are mounted above the cylinders, and where there are separate camshafts for inlet and exhaust valves

Advantages Disadvantages

-light-produces more power

-costly

References

• http://auto.howstuffworks.com/engine9.htm

• http://auto.howstuffworks.com/camshaft3.htm

• http://auto.howstuffworks.com/question366.htm