Camshaft,%20Rocker%20Arms,%20Pushrods%20(Valve%20Train)

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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

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What is a Valve Train?

• What is a Valve Train?
• Description The valve train typically 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 heads 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.

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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.

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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

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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
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• 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
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References

• http//auto.howstuffworks.com/engine9.htm
• http//auto.howstuffworks.com/camshaft3.htm
• http//auto.howstuffworks.com/question366.htm