AERA Engine Rebuilding Techniques & Procedures 4 — Questions and Answers
Question 1: What is the purpose of a pilot bearing or bushing in the crankshaft flywheel end?
- Support the rear main oil seal
- Support the transmission input shaft nose (Correct answer)
- Provide thrust surface for the flywheel
- Align the flexplate during installation
Correct answer: Support the transmission input shaft nose
The pilot bearing or bushing supports and centers the transmission or transaxle input shaft nose inside the crankshaft end.
Question 2: When Plastigage is used to check bearing clearance and shows a very wide, flat strip after cap removal, this indicates:
- Clearance is within spec
- Clearance is too tight (bearing crush too high)
- Clearance is excessive (too much oil clearance) (Correct answer)
- Correct oil film thickness
Correct answer: Clearance is excessive (too much oil clearance)
Plastigage flattens more (wider strip) when clearance is greater; a very wide strip indicates excessive oil clearance beyond specification.
Question 3: What does 'zero-deck' or 'decking to zero' mean in engine building?
- Removing all material from the block deck
- Machining the block so piston crown is exactly flush with the deck at TDC (Correct answer)
- Setting valve timing to TDC
- Balancing the crankshaft to zero grams
Correct answer: Machining the block so piston crown is exactly flush with the deck at TDC
Zero-decking means machining the block surface so the piston tops are flush with (or at a specified distance from) the deck surface at TDC, maximizing compression ratio consistency.
Question 4: Which type of valve seat insert material is required in engines designed to run on unleaded fuel without hardened OEM seats?
- Cast iron inserts
- Hardened steel or sintered iron inserts (Correct answer)
- Aluminum bronze inserts
- Stellite-faced soft iron inserts
Correct answer: Hardened steel or sintered iron inserts
Engines originally designed for leaded fuel need hardened steel or sintered iron seat inserts when converted to unleaded operation to prevent valve seat recession.
Question 5: What is the correct sequence for tightening main bearing cap bolts?
- Outside caps first, working inward
- Start at center and work outward alternately (Correct answer)
- Tighten in any order as long as final torque is correct
- Tighten all bolts one side at a time
Correct answer: Start at center and work outward alternately
Main caps should be tightened starting from the center and alternating outward to distribute clamping load evenly and minimize bore distortion.
Question 6: A connecting rod that is twisted will cause which primary symptom?
- Excessive crankshaft end play
- Uneven tire wear on the piston
- Piston scuffing on one side and abnormal ring wear (Correct answer)
- Excessive valve train noise
Correct answer: Piston scuffing on one side and abnormal ring wear
A twisted rod causes the piston to rock and run cocked in the bore, producing side scuffing on the piston skirt and uneven, accelerated ring wear.
Question 7: What is the purpose of 'deglaze honing' a cylinder before installing new piston rings on a used engine?
- Enlarge the bore to accept oversized pistons
- Break the mirror-smooth glaze so new rings can seat and seal quickly (Correct answer)
- Remove scoring from the cylinder wall
- Measure taper and out-of-round
Correct answer: Break the mirror-smooth glaze so new rings can seat and seal quickly
Deglazing creates a fresh crosshatch surface that allows new piston rings to bed into the bore rapidly for proper oil control and compression.
AERA Engine Rebuilding Techniques & Procedures 4
What is the purpose of a pilot bearing or bushing in the crankshaft flywheel end?