The valve gear shown in the illustration is...

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Question 1 of 205eccefa1bacbc34ba4d474e4

The valve gear shown in the illustration is for a four-stroke/cycle, medium speed, diesel engine, with fuel injection commencing in at 10° Before TDC. Approximately how many crankshaft degrees from the point at which fuel injection begins, does the exhaust valve push rod begin to move up? See illustration MO-0013.

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🔍 Key Concepts

• Four-stroke cycle timing – remember one full cycle is 720° of crankshaft rotation, with 180° between each stroke change (TDC↔BDC). • Fuel injection vs. valve events – injection begins shortly before TDC at the end of the compression stroke; the exhaust valve starts to open before BDC at the end of the power stroke. • Typical exhaust valve opening lead – in medium-speed diesels, the exhaust valve usually starts to open some degrees before bottom dead center on the power stroke to reduce cylinder pressure and temperature.

💭 Think About

• From the moment injection begins at 10° before TDC, trace the crankshaft rotation through the firing TDC and down the power stroke to the point where the exhaust valve first begins to lift. • How many degrees are there from TDC to BDC, and about how many degrees before BDC would you expect the exhaust valve to begin opening on a medium-speed, four-stroke diesel? • Add the angle from injection start to firing TDC to the angle from firing TDC down the power stroke to the point where the exhaust valve just starts to open. Which option best matches that total?.

✅ Before You Answer

• Be sure you use crankshaft degrees, not camshaft degrees (camshaft runs at half crankshaft speed). • Confirm that you are measuring from injection start at 10° BTDC on the compression stroke to initial exhaust valve opening near the end of the power stroke, not to full-open position or closing. • Estimate a realistic exhaust valve opening lead before BDC (typical medium-speed diesel values) and see which answer range it places your total angle in.

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