AERA Cylinder Head Rebuilding & Valve Train 2

Question 1

What effect does removing material from a cylinder head gasket surface (resurfacing) have on the valve train geometry of an overhead-cam engine?

Accepted Answer

It raises the camshaft relative to the head, reducing valve clearance and potentially increasing valve timing duration

Answer

On OHC engines, resurfacing raises the cam centerline relative to the deck, which closes up valve lash or shimmed clearances and can affect valve timing; shims or adjustments must be rechecked.

Question 2

Combustion chamber volume is measured to ensure uniformity across all cylinders. What is the primary reason for equalizing combustion chamber volumes?

Accepted Answer

To balance compression ratios and prevent uneven power output or detonation in individual cylinders

Answer

Unequal combustion chamber volumes create unequal compression ratios, causing some cylinders to run leaner/hotter and be more prone to detonation while others produce less power.

Question 3

A valve spring that measures below the minimum free-length specification should be:

Accepted Answer

Replaced, as a short free length indicates fatigue and insufficient spring pressure

Answer

A valve spring below minimum free length has taken a permanent set, indicating metal fatigue; shimming is not an acceptable repair because the spring rate may also be compromised.

Question 4

What is 'valve recession' and why is it a concern on older cast iron heads with hardened valve seats?

Accepted Answer

It is the sinking of the valve seat into the head over time, reducing valve stem height and eventually causing loss of valve adjustment

Answer

Valve recession occurs when soft iron seats wear, allowing the valve to sink deeper into the head; this shortens effective valve stem height, tightening lash on solid-lifter engines until valves stay partially open and burn.

Question 5

When selecting the correct replacement valve seat insert for a cylinder head, which dimensions are most critical?

Accepted Answer

Outside diameter, inside diameter (seat width angle), and insert height

Answer

The outside diameter determines the press-fit interference with the counterbore, the inside diameter and angle determine the seating surface, and the height must match the counterbore depth to sit flush.

(AERA) Automotive Engine Rebuilders Association Certification Practice Test

(AERA) Automotive Engine Rebuilders Association Certification Practice Test

AERA Cylinder Head Rebuilding & Valve Train 2