Question 7 DDE01 - Designated Duty Engineer - Unlimited HP

The Correct Answer is B **Explanation for Option B (Correct Answer):** The goal is to set the injector timing (follower height) while the fuel cam follower is riding on the **base circle** of the fuel cam. The base circle is the lowest lift portion of the cam profile, which represents the period when the injector is not being actuated and the cylinder is performing operations other than injection. In a standard two-stroke cycle diesel engine, the injector is actuated (fuel cam lobe is engaged) around Top Dead Center (TDC) of the compression/power stroke. When the engine is running, the exhaust valves typically open *before* Bottom Dead Center (BDC) and remain open through BDC and into the scavenging process. If you bar the engine in the direction of rotation until the \#1 cylinder's **exhaust valves are fully opened** (or around the maximum lift point for the exhaust cam, near BDC of the power stroke), this position is significantly away from the high-lift point of the fuel injection cam (which occurs near TDC). Barring the engine to BDC ensures that the fuel cam is positioned on its base circle, providing the necessary clearance and stable position to accurately measure and set the injector follower height using the specialized timing tool. **Explanation of Incorrect Options:** **A) The crankshaft should be barred in the direction of rotation until the \#1 cylinder's intake valves are fully closed.** (Note: Two-stroke engines typically use ports for scavenging/intake, but if equipped with poppet intake valves, the principle remains similar.) If the intake (scavenging) valves/ports are closing, the cylinder is approaching the beginning of the compression stroke, which means TDC (and the injection event) is imminent. This position is too close to the fuel cam lobe, making it highly likely that the follower is *not* on the base circle, or that the cam profile is rising, leading to an inaccurate timing setting. **C) The crankshaft should be barred in the direction of rotation until the \#1 cylinder's exhaust valves are fully closed.** If the exhaust valves are fully closed, the cylinder is just beginning the compression stroke, again meaning it is approaching TDC (the injection event). This position is too close to the fuel cam lobe and does not guarantee that the follower is on the base circle. **D) The crankshaft should be barred in the direction of rotation until the \#1 cylinder's intake valves are fully opened.** If the intake/scavenging valves are fully opened, the cylinder is typically near BDC, aligning closely with the position where the exhaust valves are also open (Option B). However, focusing on the *exhaust valves fully opened* (B) is the industry standard practice for finding a stable BDC/scavenging period position, which reliably places the injection cam on its base circle for timing adjustments. While D is close in timing, B is the most definitive and safest indicator for assuring the separation from the injection event.