AERA Engine Rebuilding Techniques & Procedures 5 — Questions and Answers
Question 1: When resurfacing a cylinder head, what additional check must be performed on an OHC engine before reassembly?
- Recheck valve stem height above the spring seat
- Verify camshaft bearing bore alignment after material removal (Correct answer)
- Measure valve spring free length
- Check distributor housing alignment
Correct answer: Verify camshaft bearing bore alignment after material removal
Removing material from an OHC head deck changes the cam-to-head geometry and can misalign camshaft bearing bores, requiring verification of bore alignment.
Question 2: What is 'porting' in the context of cylinder head reconditioning?
- Installing new valve guides
- Enlarging and reshaping intake and exhaust ports to improve airflow (Correct answer)
- Pressure-testing coolant passages
- Grinding valve seats to spec
Correct answer: Enlarging and reshaping intake and exhaust ports to improve airflow
Porting involves carefully enlarging, reshaping, and smoothing intake and exhaust ports to reduce flow restrictions and increase engine breathing efficiency.
Question 3: Which measurement confirms that a cylinder block's main bearing bore is properly aligned from front to rear?
- Deck surface flatness check
- Line bore alignment measured with a precision bar or laser alignment tool (Correct answer)
- Main cap bolt torque values
- Crankshaft journal micrometer readings
Correct answer: Line bore alignment measured with a precision bar or laser alignment tool
A precision alignment bar or laser tool checks whether all main bearing bores share a common centerline, confirming proper alignment before bearing installation.
Question 4: What is the effect of installing a piston with its orientation reversed (front to rear) in a non-symmetrical piston design?
- No effect if ring gaps are staggered correctly
- Offset pin bore and valve pockets will be misaligned, causing piston damage (Correct answer)
- Only affects compression ratio slightly
- Changes oil control ring function only
Correct answer: Offset pin bore and valve pockets will be misaligned, causing piston damage
Non-symmetrical pistons have offset wrist pin bores and directional valve reliefs; reversing orientation misaligns these features, potentially causing contact with valves or abnormal wear.
Question 5: After a valve job, what measurement ensures that valves are not sitting too deep in the head (excessive valve sink)?
- Valve stem protrusion above the spring retainer
- Installed valve stem height relative to a datum on the head (Correct answer)
- Valve spring coil bind clearance
- Valve seat width measurement
Correct answer: Installed valve stem height relative to a datum on the head
Measuring installed valve stem height from a reference datum on the head reveals excessive sinking of the valve into its seat, which reduces compression and may cause coil bind.
Question 6: What is the primary reason for hot tanking or jet washing a block before machining operations?
- To check for internal cracks
- To remove grease, scale, and debris so machining tools and measurements are accurate (Correct answer)
- To expand the block for accurate bore measurement
- To test core plug integrity
Correct answer: To remove grease, scale, and debris so machining tools and measurements are accurate
Cleaning removes contamination that would interfere with precision measurements and damage expensive machine tools, ensuring accurate machining results.
Question 7: Which factor most directly determines the correct piston-to-wall clearance specification for a given engine?
- Engine displacement
- Piston material and skirt design (cast vs. forged, slipper vs. full skirt) (Correct answer)
- Number of piston rings
- Bore surface finish Ra value
Correct answer: Piston material and skirt design (cast vs. forged, slipper vs. full skirt)
Piston material and skirt design dictate thermal expansion characteristics; cast pistons typically require tighter clearance than forged pistons, and skirt design affects the contact area.
AERA Engine Rebuilding Techniques & Procedures 5
When resurfacing a cylinder head, what additional check must be performed on an OHC engine before reassembly?