310S Engine Systems and Repair 4 — Questions and Answers
Question 1: What is the purpose of the oil pump pressure relief valve?
- To maintain minimum oil pressure at idle
- To prevent excessive oil pressure that could damage seals and gaskets (Correct answer)
- To filter debris from the oil supply
- To divert oil to the turbocharger at high RPM
Correct answer: To prevent excessive oil pressure that could damage seals and gaskets
The pressure relief valve opens when oil pressure exceeds a preset value, redirecting excess oil back to the sump to prevent damage to seals, gaskets, and the oil filter.
Question 2: What is indicated by a continuously fluctuating vacuum gauge reading at idle?
- Normal engine operation
- A worn camshaft lobe or weak valve spring (Correct answer)
- A restricted exhaust system
- Low engine oil level
Correct answer: A worn camshaft lobe or weak valve spring
A fluctuating vacuum reading at idle indicates inconsistent cylinder sealing, commonly caused by a worn camshaft lobe that fails to fully open a valve or a weak valve spring that allows valve float.
Question 3: When installing a new head gasket on an aluminum cylinder head, what type of fastener tightening procedure is commonly required?
- Standard torque only
- Torque-to-yield (TTY) with angle tightening (Correct answer)
- Hand-tight plus one quarter turn
- Impact wrench to maximum torque
Correct answer: Torque-to-yield (TTY) with angle tightening
Modern aluminum head engines typically use torque-to-yield (TTY) bolts that are tightened to an initial torque value and then turned an additional specified angle. TTY bolts stretch into the elastic zone for consistent clamping force and generally cannot be reused.
Question 4: What causes a spun rod bearing?
- Excessive fuel pressure
- Oil starvation or loss of oil film between the bearing and journal (Correct answer)
- Over-tightened rod bolts
- Using synthetic oil instead of conventional
Correct answer: Oil starvation or loss of oil film between the bearing and journal
A spun rod bearing occurs when the oil film is lost due to oil starvation, low oil pressure, or overheating. Metal-to-metal contact welds the bearing to the journal, causing it to spin in the connecting rod.
Question 5: What is the significance of the firing order in a multi-cylinder engine?
- It determines the fuel octane requirement
- It ensures even power distribution and minimizes vibration and crankshaft stress (Correct answer)
- It controls the oil pump output sequence
- It sets the idle speed of the engine
Correct answer: It ensures even power distribution and minimizes vibration and crankshaft stress
The firing order is designed to distribute power impulses evenly across the crankshaft rotation, minimize torsional vibrations, and reduce stress on the crankshaft and bearings.
Question 6: What condition does Plastigage measure?
- Cylinder bore taper
- Bearing oil clearance (Correct answer)
- Piston ring end gap
- Valve stem-to-guide clearance
Correct answer: Bearing oil clearance
Plastigage is a crushable plastic strip placed between the bearing and journal. When the cap is torqued, the strip flattens. Its width is compared to a scale on the package to determine oil clearance.
310S Engine Systems and Repair 4
What is the purpose of the oil pump pressure relief valve?