Engine Block Diagnosis and Repair Flashcards

A technician is installing wet cylinder liners in a heavy-duty diesel block. Each liner must be measured for protrusion above the block deck before the cylinder head is installed. What is the main purpose of the specified liner protrusion?

Answer: It lets the head gasket clamp the liner flange so the liner seals against coolant and combustion leakage

The liner flange must stand slightly above the deck so head clamping load seals the liner and gasket. Too little protrusion lets combustion gases and coolant leak, and too much can crush the gasket or distort the liner.

A diesel engine with wet cylinder liners has coolant contaminating the engine oil. The head gasket and cylinder head passed inspection, and a pressure test shows coolant leaking into the crankcase. Which is the most likely cause?

Answer: Failed lower liner O-rings or seals

On a wet-liner engine, the lower O-rings seal coolant from the crankcase. When they fail, coolant runs past the liner into the oil. The other choices do not connect coolant passages to the crankcase.

Technicians find pitting and erosion on the outside of removed wet cylinder liners, mostly on the thrust side. What is the best way to prevent this problem in service?

Answer: Keep supplemental coolant additive (SCA) at the specified concentration

The pitting is cavitation erosion, caused by liner vibration that forms and collapses vapor bubbles in the coolant. Proper SCA levels form a protective film on the liner surface and prevent it.

During block inspection, a technician finds that the main bearing bores are out of alignment after the caps are torqued. Which repair restores correct bore alignment?

Answer: Align-bore or align-hone the main bearing bores

Main bore misalignment is corrected by machining the bores in a single line, either align boring or align honing. Thicker shells or polished journals do not fix the geometry of the block.

A technician checks main bearing oil clearance with Plastigage. After the cap is torqued and removed, the flattened strip is noticeably wider at one end than at the other. What does this most likely indicate?

Answer: The journal or bore is tapered

A strip that varies in width across the bearing shows uneven clearance, which points to a tapered journal or bore. Check the journal with a micrometer to confirm.

A service procedure for a diesel engine specifies torque-to-yield (torque-angle) cylinder head bolts. What should the technician do with them?

Answer: Replace them, or reuse them only if the service information allows and they pass the length check

Torque-to-yield bolts are stretched into their plastic range during tightening, so they lose clamp consistency. Follow the manufacturer's reuse rules and length limits, otherwise replace them.

A technician measures a cylinder bore with a dial bore gauge. At the top of ring travel, thrust-direction = 4.7250 in. and axial-direction = 4.7254 in. At the bottom, thrust-direction = 4.7236 in. and axial-direction = 4.7240 in. What is the cylinder taper?

Answer: 0.0014 in.

Taper is the difference between the top and bottom diameters measured in the same direction: 4.7250 − 4.7236 = 0.0014 in. The axial readings give the same value (4.7254 − 4.7240).

After installing new piston rings, a technician hones a cylinder. What is the purpose of the cross-hatch finish left on the bore wall?

Answer: To hold oil on the wall so the rings can seat and lubricate properly

The fine cross-hatch grooves hold a film of oil and give the rings a surface to seat against. A mirror-smooth bore does not retain oil, and rings may not seat.

Which inspection method is best for finding a suspected crack in a cast iron diesel engine block?

Answer: Magnetic particle inspection

Cast iron is ferromagnetic, so magnetic particle inspection reveals cracks as particles gather at the flux leakage. Dye penetrant works on nonferrous parts too but magnetic particle is the standard method for iron.

A dial indicator is used to measure crankshaft end play. The reading is above specification. Which part is most likely worn?

Answer: The thrust bearing surfaces

Crankshaft end play is controlled by the thrust bearing, so excessive end play means the thrust faces are worn. Rod bearings and cam journals do not limit axial movement of the crankshaft.