CSLB General Building (B) — All Questions

A cylinder head is warped beyond specification. Which service is normally required to restore a flat sealing surface?

• a.Replacing the head bolts only
• b.Installing a thicker head gasket
• c.Resurfacing (machining) the head✓
• d.Retorquing the head while hot

A warped head must be resurfaced by machining to bring the deck within flatness specification. A thicker gasket will not correct an uneven surface, and simply retorquing does not remove the warp. Excessive material removal, however, can raise compression and change valve timing on some engines.

Technician A says a blown head gasket can allow coolant to enter a cylinder and cause white exhaust smoke. Technician B says it can cause bubbles in the coolant recovery tank from combustion gases. Who is correct?

• a.Technician A only
• b.Both A and B✓
• c.Technician B only
• d.Neither A nor B

A failed head gasket can leak both ways: coolant into the cylinder produces white steam-like exhaust, and combustion pressure into the cooling system produces bubbles and possible overheating. Both technicians describe valid symptoms. A cooling-system pressure test and a combustion-gas (block) test help confirm the diagnosis.

A valve that fails to seat fully will most directly cause which condition?

• a.Low cylinder compression on that cylinder✓
• b.Excessive oil consumption only
• c.High oil pressure
• d.A stuck lifter

A valve that does not seat allows combustion pressure to escape, lowering compression in that cylinder and often causing a misfire. A cylinder leak-down test with air hissing from the intake or exhaust confirms an intake or exhaust valve leak. Burned valves and carbon deposits are common causes.

On an overhead-cam engine, excessive valve lash (clearance) most commonly produces which symptom?

• a.Blue exhaust smoke
• b.Loss of coolant
• c.Low oil pressure
• d.A clicking or tapping noise from the valvetrain✓

Too much clearance in the valvetrain lets components hammer against one another, producing a rhythmic tapping that changes with engine speed. Insufficient lash, by contrast, can hold valves open and burn them. Proper adjustment restores quiet operation and correct valve timing.

Technician A says the PCV system routes crankcase blow-by vapors into the intake to be burned. Technician B says a stuck PCV valve can cause rough idle or oil leaks. Who is correct?

• a.Both A and B✓
• b.Technician A only
• c.Technician B only
• d.Neither A nor B

The PCV system draws blow-by gases into the intake so they are burned rather than vented, and a stuck valve can cause rough idle, oil leaks, or high oil consumption. Both technicians are correct. This reduces sludge formation and emissions.

A mechanic measures cylinder taper by comparing bore diameter at the top of ring travel to the bottom. This measurement is taken with a:

• a.Feeler gauge
• b.Dial bore gauge or inside micrometer✓
• c.Vacuum gauge
• d.Compression tester

Cylinder taper and out-of-round are measured with a dial bore gauge or inside micrometer at several points in the bore. Wear is greatest at the top of ring travel where combustion heat and pressure are highest. Excessive taper requires boring and oversize pistons.

Technician A says low oil pressure only at idle on a high-mileage engine can be caused by worn bearing clearances. Technician B says a worn oil pump or diluted oil can also lower pressure. Who is correct?

• a.Technician A only
• b.Technician B only
• c.Both A and B✓
• d.Neither A nor B

Worn bearing clearances let oil escape faster than the pump maintains pressure at low speed, and a worn pump or fuel-diluted oil reduces pressure as well. Both technicians are correct. Verify with a mechanical gauge before condemning parts.

Which cooling-system component regulates coolant flow based on engine temperature?

• a.Water pump
• b.Radiator cap
• c.Heater core
• d.Thermostat✓

The thermostat stays closed until the engine reaches operating temperature, then opens to allow coolant to circulate through the radiator. A stuck-closed thermostat causes overheating; a stuck-open one causes slow warm-up and poor heater output. It is a common, inexpensive cause of temperature complaints.

A radiator pressure cap raises the system's boiling point primarily because:

• a.It adds antifreeze to the coolant
• b.Increased pressure raises the coolant's boiling temperature✓
• c.It lowers the coolant level
• d.It speeds up the water pump

Sealing the system under pressure raises the boiling point of the coolant, allowing higher operating temperatures without boil-over. A weak or faulty cap lowers the effective boiling point and can cause coolant loss. Caps should be pressure-tested when overheating is suspected.

Blue smoke from the exhaust under acceleration most often indicates:

• a.A rich fuel mixture
• b.Coolant in the combustion chamber
• c.Oil entering the combustion chamber✓
• d.A lean misfire

Blue smoke indicates oil is being burned, commonly from worn rings, cylinder walls, or valve guide seals. White smoke suggests coolant, and black smoke suggests excess fuel. A leak-down or compression test helps localize the source.

Technician A says timing-chain stretch can retard valve timing and set a camshaft/crankshaft correlation code. Technician B says a stretched timing chain has no effect on engine performance. Who is correct?

• a.Technician A only✓
• b.Both A and B
• c.Technician B only
• d.Neither A nor B

A stretched or worn timing chain changes the relationship between crankshaft and camshaft position, retarding valve timing and often setting a correlation DTC. This can cause rough running and reduced power. Technician B is incorrect because timing is directly affected.

Head bolts that use a torque-to-yield (TTY) design should be:

• a.Reused indefinitely
• b.Torqued to half the final value only
• c.Replaced with new bolts during reassembly✓
• d.Coated with anti-seize before reuse

Torque-to-yield bolts are stretched into their plastic range for a uniform clamp load and should not be reused. Reusing them risks uneven clamping and gasket failure. Always follow the specified torque-plus-angle sequence with new bolts.

The main function of engine oil, besides lubrication, includes all of the following EXCEPT:

• a.Cooling internal components
• b.Generating spark for combustion✓
• c.Cleaning and suspending contaminants
• d.Sealing between rings and cylinder walls

Engine oil lubricates, cools, cleans, and helps seal the rings, but it plays no role in generating spark. Spark is produced by the ignition system. Detergent and dispersant additives keep contaminants suspended until the filter or an oil change removes them.

A rhythmic knocking noise that is loudest under load and disappears when one cylinder is disabled most likely indicates:

• a.A loose accessory belt
• b.An exhaust leak
• c.A sticking valve
• d.A worn connecting-rod bearing on that cylinder✓

A rod bearing knock is load-sensitive and typically quiets when that cylinder's contribution is removed by disabling its injector or spark. Loose belts and exhaust leaks make different noises unrelated to individual cylinders. Excessive rod bearing clearance is confirmed with Plastigage during disassembly.

Coolant is leaking internally and the engine oil appears milky. The MOST likely cause is:

• a.A worn timing belt
• b.A clogged air filter
• c.A failed head gasket or cracked block/head✓
• d.A stuck thermostat

A milky, tan appearance in the oil indicates coolant contamination, commonly from a head gasket failure or a crack that connects a coolant passage to the oil. Continued operation damages bearings. Pressure and combustion-gas testing help pinpoint the leak path.

Before final assembly, plastigage is used to measure:

• a.Valve spring free length
• b.Bearing oil clearance✓
• c.Cylinder bore taper
• d.Piston ring end gap

Plastigage is a crushable plastic thread that indicates bearing oil clearance when compared to a scale after the cap is torqued. Ring end gap is measured with a feeler gauge in the bore, and bore taper with a bore gauge. Correct clearance is essential for oil film and bearing life.