🔍 Key Concepts

• Meaning of a fuel pump being timed for port closing in a diesel engine • How a jerk-type fuel injection pump controls start and end of injection • Difference between start of injection vs duration/amount of injection

💭 Think About

• Think about what event the timing mark is actually referencing when the pump is described as timed for port closing—is it the start or end of delivery? • Ask yourself: on a conventional fuel injection pump with a helix-controlled plunger, what stays fixed with respect to crank angle, and what changes when you move the fuel control rack? • Consider which component (plunger stroke, delivery valve, or timing marks) is normally used to meter fuel quantity in a standard marine diesel fuel pump.

✅ Before You Answer

• Be clear on whether port closing in the pump barrel is associated with the beginning or end of fuel delivery. • Verify which part of the system usually meters fuel quantity—the plunger stroke/control rack or the delivery valve. • Check if proper timing practice would ever normally require changing timing reference marks, or if those marks are intended to stay fixed once set.