AERA AERA Engine Measurement & Machining Tolerances 1 — Questions and Answers
Question 1: What instrument is most commonly used to measure cylinder bore diameter to verify it is within AERA tolerance specifications?
- Bore gauge (cylinder dial bore gauge) (Correct answer)
- Feeler gauge
- Outside micrometer
- Vernier caliper
Correct answer: Bore gauge (cylinder dial bore gauge)
A cylinder dial bore gauge provides the precise inside diameter measurements needed to compare against AERA tolerance specifications for reboring or honing decisions.
Question 2: According to AERA guidelines, what term describes the maximum allowable variation in a crankshaft's main journal diameter along its length?
- Taper (Correct answer)
- Runout
- Ovality
- End play
Correct answer: Taper
Taper refers to the difference in diameter measured at opposite ends of a journal, and AERA sets maximum taper limits to ensure proper bearing fit and oil film.
Question 3: When measuring crankshaft journal out-of-round (ovality), the measurement is taken at how many positions around the journal?
- At least two positions 90° apart (Correct answer)
- At least four positions 45° apart
- One position only
- Three positions 60° apart
Correct answer: At least two positions 90° apart
Measuring at two positions 90° apart reveals the maximum and minimum diameters, which when subtracted give the out-of-round value for comparison to AERA limits.
Question 4: Which type of micrometer is specifically designed to measure the inside diameter of a camshaft bearing bore?
- Telescoping gauge used with an outside micrometer
- Inside micrometer (tubular) (Correct answer)
- Depth micrometer
- Thread micrometer
Correct answer: Inside micrometer (tubular)
An inside micrometer with tubular extensions can directly measure larger bore diameters like camshaft bores with high precision.
Question 5: AERA recommends measuring cylinder bore diameter at a minimum of how many depths to check for taper?
- At least two depths — near the top and near the bottom of ring travel (Correct answer)
- One depth at mid-stroke only
- Three depths including below ring travel
- Four depths at equal intervals
Correct answer: At least two depths — near the top and near the bottom of ring travel
Measuring near the top and bottom of ring travel identifies taper wear since the cylinder wears most at the top of ring travel.
Question 6: What is the purpose of checking crankshaft main bearing journal runout with a dial indicator and V-blocks?
- To detect crankshaft straightness (bend) (Correct answer)
- To measure journal surface finish
- To verify oil hole alignment
- To check end play clearance
Correct answer: To detect crankshaft straightness (bend)
Placing the crankshaft on V-blocks and rotating it past a dial indicator reveals total indicated runout, indicating whether the crank is bent beyond AERA limits.
AERA AERA Engine Measurement & Machining Tolerances 1
What instrument is most commonly used to measure cylinder bore diameter to verify it is within AERA tolerance specifications?