ASE Engine Repair A1

Question 1

What is the primary function of the camshaft in an internal combustion engine?

Accepted Answer

To control the timing and operation of intake and exhaust valves

Answer

The camshaft controls the opening and closing of the intake and exhaust valves in sync with piston movement. It is driven by the crankshaft via a timing belt, chain, or gears at half the crankshaft speed in a 4-stroke engine.

Question 2

A technician measures excessive crankshaft end play during an engine rebuild. What is the MOST likely cause?

Accepted Answer

Worn or damaged thrust bearings

Answer

Crankshaft end play is controlled by thrust bearings (thrust washers). Worn or damaged thrust bearings allow excessive axial movement of the crankshaft. If end play exceeds specification, the thrust bearings must be replaced.

Question 3

Which condition would MOST likely cause low compression in one cylinder while all others test normal?

Accepted Answer

A burned or bent valve

Answer

A burned or bent valve prevents the combustion chamber from sealing properly during the compression stroke, resulting in low compression in that cylinder only. Worn piston rings affect multiple cylinders more evenly, while a cracked block or head gasket failure typically affects adjacent cylinders.

Question 4

When performing a cylinder leak-down test, air escaping from the oil filler cap indicates leakage past which component?

Accepted Answer

Worn or damaged piston rings

Answer

Air escaping from the oil filler cap during a leak-down test indicates combustion gases are leaking past the piston rings into the crankcase (blow-by). Air at the throttle body or air filter suggests intake valve leakage; air at the exhaust pipe suggests exhaust valve leakage; air at the radiator suggests a head gasket leak.

Question 5

What is the purpose of measuring main and rod bearing clearance with Plastigage during an engine rebuild?

Accepted Answer

To verify the oil film clearance between the bearing and crankshaft journal

Answer

Plastigage is a soft plastic thread placed between the bearing and journal before torquing the cap. After disassembly, the width of the crushed Plastigage is compared to a scale to determine oil clearance. Correct clearance ensures an adequate hydrodynamic oil film that prevents metal-to-metal contact and premature bearing wear.

ASE Practice Test

ASE Practice Test

ASE Engine Repair A1