🔍 Key Concepts

• In a four-stroke cycle, the crankshaft turns 720° for a full cycle, and each stroke ideally covers about 180° of crank rotation. • The polar timing diagram shows events as colored arcs; you must identify which colored arc represents the power event (expansion stroke). • Pay close attention to the degree markings (85°, 125°, etc.) and whether they mark the full span of the power arc or just a portion (such as start or end offsets).

💭 Think About

• Which specific colored sector on the diagram corresponds to the power/expansion stroke, and between which crank positions (TDC/BDC) does it occur? • Do the numbers 85° and 125° on the inner arc mark the beginning and end of the power event, or are they relative to TDC/BDC (e.g., before or after)? • If you follow the direction of rotation, what is the total angular distance covered by the power event from its start to its finish as shown on the red arc?

✅ Before You Answer

• Be sure you correctly identify TDC (top dead center) and BDC (bottom dead center) and the direction of crankshaft rotation on the diagram. • Confirm exactly where the red arc (power event) starts and ends with respect to the radial reference lines and the degree labels. • Verify whether you should add or compare the degree values shown (85° and 125°) to determine the total crankshaft degrees for the power event.