310S Engine Systems and Repair 3 — Questions and Answers
Question 1: What tool is used to measure the installed height of a valve spring?
- Dial indicator
- Spring scale
- Vernier caliper or spring height micrometer (Correct answer)
- Feeler gauge
Correct answer: Vernier caliper or spring height micrometer
A vernier caliper or dedicated spring height micrometer is used to measure the installed height of valve springs from the spring seat to the underside of the retainer.
Question 2: What is the purpose of the piston pin offset in modern engines?
- To increase compression ratio
- To reduce piston slap during the transition from compression to power stroke (Correct answer)
- To allow for easier piston installation
- To balance the reciprocating mass
Correct answer: To reduce piston slap during the transition from compression to power stroke
The piston pin is offset slightly toward the thrust side to reduce the impact force (piston slap) as the piston transitions from the compression stroke to the power stroke, reducing noise and wear.
Question 3: A technician measures 0.08 mm (0.003 in.) of main bearing oil clearance. The specification is 0.02–0.05 mm. What action is required?
- This is acceptable; no action needed
- Replace the main bearings with the correct undersize (Correct answer)
- Machine the crankshaft journals to the next oversize
- Add thicker oil to compensate for the clearance
Correct answer: Replace the main bearings with the correct undersize
Excessive oil clearance reduces oil pressure and lubrication effectiveness. The bearings must be replaced. If the crankshaft journals are within specification, standard bearings or the correct undersize bearings are installed.
Question 4: What happens to an interference engine when the timing belt breaks?
- The engine stalls but no damage occurs
- The pistons contact the open valves, causing engine damage (Correct answer)
- The engine runs rough but continues to operate
- Only the water pump fails
Correct answer: The pistons contact the open valves, causing engine damage
In an interference engine, the valves and pistons occupy the same space at different times. When the timing belt breaks, valves remain open and are struck by the pistons, causing bent valves and potential piston damage.
Question 5: What is the function of the positive crankcase ventilation (PCV) valve?
- To vent exhaust gases to the atmosphere
- To regulate the flow of crankcase vapours back into the intake for combustion (Correct answer)
- To control oil pressure in the crankcase
- To prevent coolant from entering the crankcase
Correct answer: To regulate the flow of crankcase vapours back into the intake for combustion
The PCV valve meters crankcase blow-by gases back into the intake manifold to be burned during combustion, reducing emissions and preventing crankcase pressure buildup.
Question 6: A technician is checking camshaft endplay. Which measuring tool is most appropriate?
- Outside micrometer
- Dial indicator mounted to the block with the camshaft pushed fore and aft (Correct answer)
- Plastigage strip
- Cylinder bore gauge
Correct answer: Dial indicator mounted to the block with the camshaft pushed fore and aft
Camshaft endplay (axial movement) is measured using a dial indicator mounted to the engine block while pushing the camshaft forward and backward to measure the total movement.
310S Engine Systems and Repair 3
What tool is used to measure the installed height of a valve spring?