You are about to check the valve lash adjustment on #1 cylinder's intake and exhaust valves of an auxiliary diesel engine fitted on the anchor-handling supply vessel to which you are assigned. You want to adjust the valve lash on both valves without having to reposition the crankshaft between adjustments. What should be the position of #1 piston to insure both the intake and exhaust valves are both in a position to facilitate valve adjustment?
• Four-stroke diesel cycle: intake, compression, power, exhaust • Valve positions during each stroke (when are both valves closed?) • Purpose of valve lash adjustment: done when cam followers are on the base circle of the cam
• For both intake and exhaust valves to be correctly adjusted at the same time, what must be true about the cam position relative to each valve? • During which stroke is the piston at or near TDC with both valves fully seated rather than opening or closing? • Think about the difference between TDC at the end of compression vs. TDC at the end of exhaust in terms of valve timing and overlap.
• Identify during which stroke both intake and exhaust valves are fully closed for cylinder #1. • Verify that at the chosen crankshaft position, each valve tappet is on the base circle of its cam lobe, not on the ramp or nose. • Confirm you are not in a period of valve overlap (one valve closing while the other is starting to open) at or near TDC.
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