The four cams shown in the illustration are...

Question 1 of 270705eccefa3bacbc34ba4d47d48

The four cams shown in the illustration are in position with their respective pistons at top dead center. Which of the cams is the air starting cam? See illustration MO-0045.

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Question 1 of 27070

The four cams shown in the illustration are in position with their respective pistons at top dead center. Which of the cams is the air starting cam? See illustration MO-0045.

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🔍 Key Concepts

• Relationship between starting air valve opening and piston position near top dead center (TDC) • Shape of a cam that must hold a valve open for a relatively long period around TDC versus a cam for quick events like fuel injection • How symmetry of the cam lobe around TDC relates to when the valve opens and closes

💭 Think About

• For starting an engine, when should compressed air begin to enter the cylinder relative to TDC, and how long must it continue to act to turn the crank? • Which cam profile would keep the follower lifted (valve open) for the broadest, most centered interval around TDC, rather than a short, sharply timed event? • Compare each cam: if the crank is at TDC now, where is the highest part of the lobe relative to the vertical axis, and what does that say about valve timing?

✅ Before You Answer

• Identify which cam has its maximum lift centered on TDC (vertical axis) instead of clearly before or after it • Check which cam provides the widest high-lift area (a dwell) around TDC, suitable for sustained starting air admission • Eliminate any cam shapes that look like they would cause only a brief, sharply timed lift just before TDC (typical of fuel injection, not starting air)