Five free practice questions on engine block and bottom end: content area C of the ASE T2 Diesel Engines test, 5 of its 55 scored questions (9.1%). They are in the ASE format: four options, one best answer. Answer each one before opening the explanation. No account, no email.
01The questions
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A truck's turbocharged diesel engine pushes oil out of its dipstick tube, and a gauge at the tube reads crankcase pressure above the manufacturer's limit under load. Any of these could be the cause EXCEPT:
- a restricted crankcase breather filter.
- worn piston rings and cylinder liners.
- a restricted engine air filter.
- leaking turbocharger shaft seals.
Show the answer
C. Correct. A restricted air filter raises the vacuum at the turbocharger inlet; it costs boost and power and can draw oil past the turbocharger's compressor-side seal, but it adds no gas to the crankcase. Crankcase pressure rises when more gas enters the crankcase than the ventilation system can carry away.
Why not the others
A. This could cause it: the breather or ventilation filter is the way blowby leaves the crankcase, so when it plugs, even normal blowby builds pressure. The restricted air filter is the one choice that adds no gas to the crankcase.
B. This could cause it: worn rings and liners let combustion gas blow by into the crankcase, which is the most familiar reason crankcase pressure climbs under load. The restricted air filter is the one choice that puts no gas into the crankcase.
D. This could cause it: boost leaking past the compressor-side seal, or exhaust gas past the turbine-side seal, enters the bearing housing and flows down the oil drain into the crankcase. The restricted air filter is the one choice that adds no gas to the crankcase.
ID T2-C-003 · Task T2-C-1 (ASE task list)
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During block inspection, the technician checks deck height at both ends of a diesel engine block and compares it with the manufacturer's dimension. What does deck height measure?
- The height of each liner flange above the deck
- The flatness of the deck across its length and width
- The height of each piston above the deck at TDC
- The distance from the main bore center to the deck
Show the answer
D. Correct. Deck height runs from the crankshaft's main bore centerline up to the head-mounting surface, so it shows whether the deck has been machined before and how much more may be removed. It sets how high the pistons and liners stand relative to the deck, and checking it at both ends also shows whether the deck is parallel to the crankshaft.
Why not the others
A. That is liner protrusion, measured with the liners clamped in the block. Deck height is a dimension of the block itself: the distance from the main bore centerline up to the deck surface.
B. Flatness is checked with a straightedge and feeler gauge laid across the deck, and it shows warpage, not height. Deck height is the distance from the main bore centerline up to the deck surface.
C. That is piston protrusion, measured with a dial indicator as each piston is brought to top dead center. Deck height is a dimension of the bare block: the distance from the main bore centerline up to the deck.
ID T2-C-004 · Task T2-C-2 (ASE task list)
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An in-block camshaft from a diesel engine is on the bench at an overhaul, and the manufacturer lists a maximum runout (bend) for it before it can be reused. How is that runout measured?
- Roll it across a surface plate and watch for rocking
- Mic each journal twice, 90 degrees apart
- Turn it in V-blocks, indicating a center journal
- Indicate the gear face as the camshaft is pried fore and aft
Show the answer
C. Correct. With the end journals resting in V-blocks, a dial indicator on a center journal reads how far that journal swings off the shaft's axis as the camshaft is turned through a full revolution, and the total indicator reading is compared with the manufacturer's maximum. A camshaft over the limit is replaced as the manufacturer directs, since a bent shaft loads its bushings unevenly.
Why not the others
A. Rolling on a flat plate is a quick straightness check for a push tube, but a camshaft's lobes and gear keep it from rolling true, and the method gives no reading to compare with a limit. Runout is read on a dial indicator as the camshaft is turned on its end journals in V-blocks.
B. Two micrometer readings at 90 degrees find journal wear, taper and out-of-round, which have their own limits; a bent camshaft can still have round journals of the right size. Bend shows as a center journal swinging off the shaft's axis when the camshaft is turned in V-blocks under a dial indicator.
D. Prying the camshaft fore and aft against a dial indicator measures end play, the lengthwise movement set by the thrust surfaces, not bend. Runout is read on a center journal while the camshaft turns on its end journals in V-blocks.
ID T2-C-007 · Task T2-C-7 (ASE task list)
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When a crankshaft from a high-mileage diesel engine is inspected for cracks, the journal fillets and the edges of the oil holes get the closest look. Why?
- Bearing heat is highest there
- Bearing wear is greatest at those points
- Sludge collects there and corrodes
- Stress concentrates there under load
Show the answer
D. Correct. A fillet is where a journal meets a crankshaft web, and an oil hole is an opening through a heavily loaded journal; both change the section abruptly, so the bending and twisting stress of every power stroke peaks there. Fatigue cracks start at those stress raisers, which is why a reground crankshaft must keep the fillet radius the manufacturer specifies.
Why not the others
A. Heat from a distressed bearing shows on the journal surface as discoloration, not concentrated at the fillets. The fillets and oil-hole edges get the closest look because the bending and twisting stress concentrates there and starts fatigue cracks.
B. The bearing shells do not even touch the fillets, and bearing wear shows on the journal's bearing surface. The fillets and oil-hole edges are watched because the stress of each power stroke concentrates there and starts fatigue cracks.
C. Sludge collects in the drilled passages and plug cavities, which are cleaned for that reason, but it does not make the fillets and oil-hole edges crack. Those areas are inspected because stress concentrates there and fatigue cracks begin there.
ID T2-C-008 · Task T2-C-8 (ASE task list)
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To find piston-to-liner clearance, a technician measures a diesel piston's skirt with an outside micrometer at the height the manufacturer specifies. In which direction is the skirt measured?
- In line with the pin, across the pin bosses
- Across the thrust faces, 90 degrees to the pin
- At 45 degrees between the pin and thrust faces
- In any direction, since the skirt is round
Show the answer
B. Correct. Piston skirts are typically ground slightly oval and tapered so they fit the bore at operating temperature, and the manufacturer's skirt diameter is taken across the thrust faces, at right angles to the pin. The clearance is the liner bore measured where the manufacturer specifies, minus that skirt diameter.
Why not the others
A. Across the pin bosses is the narrow axis of an oval-ground skirt, so the reading would come out small and the clearance would look too large. The skirt is measured across the thrust faces, at right angles to the pin.
C. A diagonal reading falls between the narrow and wide axes of the skirt and matches no specification. The manufacturer's skirt diameter is taken across the thrust faces, at right angles to the pin.
D. Piston skirts are typically ground slightly oval and tapered, so the diameter changes with direction. The skirt is measured across the thrust faces, at right angles to the pin, at the height the manufacturer gives.
ID T2-C-011 · Task T2-C-12 (ASE task list)
02Answer key
| Question | Answer |
|---|---|
| Q1 | C |
| Q2 | D |
| Q3 | C |
| Q4 | D |
| Q5 | B |
03What area C covers
This content area covers the engine block and the parts inside it: pans, covers and crankcase ventilation, block inspection and deck height, counterbores and wet liners with their seals and protrusion, in-block camshafts, the crankshaft with its main and rod bearings, the front gear train, pistons, rings and connecting rods, vibration dampers, the flywheel housing and flywheel, and block heaters.
The ASE test specification calls this content area “Engine Block Diagnosis and Repair”. It carries 5 of the 55 scored questions, 9.1% of the test.
- Service pans, covers, seals and crankcase ventilation
- Inspect the block and measure deck height
- Check liner bores for wear, cavitation and distortion
- Install wet liners and set liner protrusion
- Measure crankshaft journals, bearings and end play
- Time the gear train and measure backlash
- Fit pistons, rings and rods and check piston protrusion
- Inspect dampers, flywheel housing, flywheel and block heaters
04What the questions turn on
Cavitation on wet liners
Pits on the coolant side of a wet liner, heaviest on the thrust sides, are cavitation: the vibrating wall forms vapor bubbles that collapse against it. Liner-protecting additive at the specified level, in a full, pressurized system, guards against it.
Read every protrusion number
Liner protrusion has more than one limit. Each reading can sit inside the range while one liner's four readings spread more than allowed, which points to an uneven counterbore ledge or dirt or a burr under the flange.
Backlash points to the part
When backlash is high at both meshes of the idler gear but normal at a mesh that does not involve it, the idler is floating on a worn bushing. The bushing clearance confirms it, and every mesh is measured again after the repair.
Crush holds the bearing
A bearing shell is held still by crush, since it is slightly larger around than its bore. A rod big-end bore stretched oversize no longer grips the shell, so it creeps, frets and spins, and the rod is resized or replaced.
05The other content areas
The T2 test has eight content areas. Each has its own page of free questions:
The ASE T2 Diesel Engines practice test page describes the full question bank. How these questions are written and checked: how our questions are made. Found a mistake? Tell us and we will fix it.
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