EGSA Generator Set Maintenance 4 — Questions and Answers
Question 1: What is the purpose of a scheduled valve lash adjustment on a diesel generator engine?
- To adjust fuel injection timing
- To maintain proper clearance between valve stems and rocker arms for correct valve opening and closing (Correct answer)
- To set the engine governor sensitivity
- To calibrate the turbocharger boost pressure
Correct answer: To maintain proper clearance between valve stems and rocker arms for correct valve opening and closing
Valve lash settings ensure valves open and close at the correct time and duration; incorrect lash causes power loss, poor combustion, or valve damage.
Question 2: When inspecting a generator's vibration isolation mounts during routine maintenance, which condition requires immediate replacement?
- Minor surface cracking on the rubber
- Complete separation, compression set greater than 30%, or oil saturation of the rubber element (Correct answer)
- Slight discoloration of the metal brackets
- Mounting bolts showing surface rust
Correct answer: Complete separation, compression set greater than 30%, or oil saturation of the rubber element
Separated, severely compressed, or oil-soaked mounts can no longer isolate vibration, allowing damaging forces to transfer to the generator frame and foundation.
Question 3: A generator set's engine governor is hunting (repeated speed fluctuation) at no load. Which maintenance action should be performed first?
- Replace the governor actuator motor
- Check and adjust governor droop setting and inspect linkage for binding or wear (Correct answer)
- Replace the fuel injection pump
- Increase battery float charge voltage
Correct answer: Check and adjust governor droop setting and inspect linkage for binding or wear
Governor hunting is often caused by worn linkage creating feedback instability or incorrect droop settings; these should be inspected and adjusted before replacing components.
Question 4: What is the recommended maximum time interval for exercising a standby diesel generator set under load to prevent fuel degradation and maintain readiness?
- Monthly under load for at least 30 minutes (Correct answer)
- Quarterly without load for 10 minutes
- Bi-annually under load for 1 hour
- Weekly at no load for 5 minutes only
Correct answer: Monthly under load for at least 30 minutes
NFPA 110 and most manufacturers recommend monthly loaded exercise for a minimum of 30 minutes to maintain fuel system conditioning and verify operational readiness.
Question 5: During a maintenance inspection, a technician notices the turbocharger compressor wheel has small nicks and erosion marks. What is the most likely cause?
- Over-fueling during load acceptance
- Air filter bypass allowing dirt ingestion into the intake (Correct answer)
- Excessive exhaust back pressure
- Low engine oil pressure
Correct answer: Air filter bypass allowing dirt ingestion into the intake
Erosion and pitting on the compressor wheel are caused by abrasive particles entering through a compromised or missing air filtration system.
Question 6: What is the significance of monitoring wet bulb temperature when performing generator cooling system evaluations?
- It determines the required oil viscosity grade
- It establishes the minimum achievable coolant temperature, affecting radiator sizing and heat rejection capacity (Correct answer)
- It sets the thermostat opening temperature
- It is used to calculate fuel consumption rates
Correct answer: It establishes the minimum achievable coolant temperature, affecting radiator sizing and heat rejection capacity
Wet bulb temperature defines the thermodynamic limit for heat rejection; ambient wet bulb values must be factored into cooling capacity calculations especially in humid climates.
Question 7: When performing a 5,000-hour major overhaul on a diesel generator set, which component is typically evaluated using Plastigage during reassembly?
- Fuel injector nozzle wear
- Crankshaft main and rod bearing clearances (Correct answer)
- Camshaft lobe profile
- Valve spring free length
Correct answer: Crankshaft main and rod bearing clearances
Plastigage is a precision measurement method used to verify main and connecting rod bearing oil clearances during engine assembly to ensure proper lubrication film thickness.
EGSA Generator Set Maintenance 4
What is the purpose of a scheduled valve lash adjustment on a diesel generator engine?