According to the illustrated polar timing...

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Question 1 of 205eccefa1bacbc34ba4d473d9

According to the illustrated polar timing diagram for a four- stroke cycle high speed diesel engine, the period of valve overlap occurs for a duration of how many degrees of crank travel? See illustration MO-0084.

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🔍 Key Concepts

• Valve overlap occurs when both the intake and exhaust valves are open at the same time, usually around TDC between the exhaust and intake strokes. • On a polar timing diagram, each colored ring or band represents when a particular valve is open in terms of crankshaft degrees. • You find the duration of overlap by adding the degrees before TDC that one valve opens to the degrees after TDC that the other valve closes.

💭 Think About

• From the diagram, identify which band is the intake valve open period and which is the exhaust valve open period. Where do these two bands intersect around TDC? • Read the angle marks near TDC: how many degrees before TDC does the intake valve begin to open, and how many degrees after TDC does the exhaust valve finish closing? • Once you have those two angle values, what total crank angle do you get when you add them together? Which answer choice is closest to that total?

✅ Before You Answer

• Make sure you are measuring only the region where both valves are open at the same time, not the full open period of either valve alone. • Confirm that you are using angles referenced to TDC, not BDC, for the overlap calculation. • Double-check that you are adding the before-TDC portion of one valve event to the after-TDC portion of the other, and that your sum matches one of the answer choices.

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