Five free practice questions on engine block, crankshaft and pistons: content area C of the ASE A9 Light Vehicle Diesel Engines test, 5 of its 50 scored questions (10%). 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 replacement rear crankshaft seal with a PTFE (polytetrafluoroethylene) lip comes mounted on a plastic sleeve. What is the sleeve for?
- A running surface left on the crankshaft flange
- Protecting the lip in shipping; it comes off first
- Holding the lip open to slide onto the flange
- Keeping the lip clean until it is oiled
Show the answer
C. Correct. A PTFE lip is stiff and is made smaller than the flange, so the sleeve keeps it stretched until the seal is pushed off the sleeve onto the flange, and the sleeve is then removed. Without it the lip can fold over or tear on the flange edge and the seal leaks from the start.
Why not the others
A. A wear sleeve that stays on a grooved flange is a separate, thin metal part. This plastic sleeve only holds the PTFE lip open so it passes onto the flange undamaged, and it is removed once the seal is installed.
B. Taking the sleeve off before installation lets the stiff PTFE lip close down below the flange size, so it can fold or tear going on. The sleeve stays in the seal until it is installed because it holds the lip open to pass over the flange.
D. The sleeve is not a dust cover, and PTFE-lip seals are commonly installed dry, as their instructions direct. Its job is to keep the lip stretched so it slides onto the crankshaft flange without folding or tearing.
ID A9-C-003 · Task A9-C-1 (ASE task list)
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A new crankshaft is going into a light-duty diesel whose manufacturer supplies main bearing shells in several thickness grades. The block carries a size code for each main bore, and the crankshaft a size code for each main journal. How is the shell grade for each main chosen?
- The grade on the old shell from that main
- The grade that matches the journal code alone
- The chart grade for its bore and journal code
- The thickest grade that lets the crank turn
Show the answer
C. Correct. Bore and journal sizes each vary within their machining tolerances, and select fitting matches the shell thickness to the pair so every main ends up with oil clearance in a narrow range. The manufacturer's chart crosses the two codes to give the grade, and the clearance is then confirmed as the manufacturer directs.
Why not the others
A. The old shell was chosen for the old crankshaft's journal, and the new crankshaft's codes may differ. The grade comes from the manufacturer's chart using this bore's code and the new journal's code.
B. The journal code is only half of the selection: the bore code tells how large the housing is, and the same journal can need a different shell in a larger or smaller bore. The manufacturer's chart takes both codes.
D. A crankshaft can turn freely with clearance anywhere from tight to excessive, so turning it does not measure clearance. The grade is read from the manufacturer's chart for the bore and journal codes, then the clearance is checked.
ID A9-C-008 · Task A9-C-7 (ASE task list)
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The main bearing caps of a light-duty diesel are numbered, and each carries a direction arrow. Any of these is correct practice when the caps are refitted during an overhaul EXCEPT:
- fitting each cap at the position its number shows.
- facing each cap's arrow the way it is specified.
- tightening the cap bolts in the specified sequence.
- filing the cap faces to reduce the oil clearance.
Show the answer
D. Correct. Filing a cap's parting faces closes up its main bore, leaving it out of round and out of line with the other bores, so the shells are pinched and the crankshaft can bind. Excess clearance is corrected with the right bearings or crankshaft repair, and a distorted bore with align boring, never by filing caps.
Why not the others
A. This is correct practice. Each cap was machined in place with the block when the main bores were finished, so it fits only its own position. Filing the cap faces is the exception.
B. This is correct practice. A cap turned end for end leaves its half of the bore offset from the block's half, so each arrow faces the direction the manufacturer specifies. Filing the cap faces is the exception.
C. This is correct practice. Tightening the bolts in steps and in the manufacturer's sequence draws each cap down evenly so the bore keeps its shape. Filing the cap faces is the exception.
ID A9-C-009 · Task A9-C-8 (ASE task list)
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Before calculating piston-to-cylinder clearance, a technician measures a new aluminum piston's skirt right after it came out of a hot parts washer, while the cast-iron block is at shop temperature. How will the warm piston affect the clearance the technician calculates?
- It will come out smaller than the true clearance
- It will come out larger than the true clearance
- No effect, as aluminum and iron expand alike
- No effect, as the skirt is ground to allow for heat
Show the answer
A. Correct. Aluminum grows considerably more with heat than cast iron, so the warm skirt measures larger than it will be at shop temperature, and bore minus skirt gives a clearance smaller than the true figure. Both parts are measured at the same room temperature so the result can be compared with the manufacturer's specification.
Why not the others
B. The direction is reversed. A warm aluminum skirt has grown, so it measures larger than it will be when cool, and subtracting a larger skirt from the bore gives a smaller clearance, not a larger one.
C. Aluminum expands considerably more with heat than cast iron, which is one reason pistons need clearance at all. The warm skirt reads oversize, and the calculated clearance comes out smaller than the true one.
D. The skirt's shape is designed to fit the bore at operating temperature, but the manufacturer's clearance is for parts measured at room temperature. A skirt measured warm reads oversize, so the calculated clearance comes out too small.
ID A9-C-011 · Task A9-C-11 (ASE task list)
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A taper-faced second compression ring carries an identification mark that the manufacturer says must face the piston crown. If the ring is installed upside down, what does this cause?
- Higher compression in that cylinder
- A ring end gap below the minimum
- A ring that binds in its groove when hot
- More oil reaching the combustion chamber
Show the answer
D. Correct. A taper-face ring touches the wall at its lower edge, so it scrapes oil downward on the down stroke and rides over the oil film on the up stroke. Upside down, the scraping edge is on top and pumps oil up toward the combustion chamber, raising oil consumption.
Why not the others
A. An inverted second ring does not seal compression any better. Its scraping edge, now on top, pumps oil up past the rings into the combustion chamber, so the result is higher oil consumption.
B. End gap depends on the ring and the bore it sits in, not on which side faces up. Turning the ring over reverses the direction its tapered face scrapes, so it pumps oil up toward the combustion chamber.
C. Flipping the ring does not change its height in the groove, so side clearance and the chance of binding stay the same. What changes is the taper's direction, which then scrapes oil upward into the combustion chamber.
ID A9-C-014 · Task A9-C-13 (ASE task list)
02Answer key
| Question | Answer |
|---|---|
| Q1 | C |
| Q2 | C |
| Q3 | D |
| Q4 | A |
| Q5 | D |
03What area C covers
This content area covers the block of a pickup or van diesel and what turns inside it: pans, covers and rear seals, block inspection, dowels and deck height, cylinder bore wear and honing, in-block camshafts and their bearings, the crankshaft and select-fit bearings, the gear train, pistons, pins, rings and rods, piston cooling jets, vibration dampers, and flywheels and flexplates.
The ASE test specification calls this content area “Engine Block Diagnosis and Repair”. It carries 5 of the 50 scored questions, 10% of the test.
- Replace pans, covers, gaskets, seals and wear rings
- Inspect the block, dowels, deck and passages
- Measure cylinder wear and decide on bore service
- Replace in-block camshaft bearings and check end play
- Choose select-fit bearings and check main clearances
- Time and inspect the gear, chain or belt drive
- Fit pistons, pins, rings, rods and cooling jets
- Inspect dampers, flywheels, flexplates and ring gears
04What the questions turn on
Read the wear pattern
Wear location points to the cause. Main shells worn bright along both edges, centers barely touched, point to a journal larger at its ends than its middle. A bore gouge in line with the piston pin points to a retainer that left its groove.
New range or service limit
A used piston is judged against the service limit, not the new-part range. Ring side clearance over the new maximum but under the service limit means a worn groove that is still reusable. A new ring is used so only groove wear shows.
Never file the caps
Filing a main cap's parting faces closes up its bore, leaving it out of round and out of line. Fracture-split rod caps fit only the rod they were broken from, one way round, and their rough faces are kept clean, never filed.
Measure it as it will run
Head-bolt load distorts the bores slightly, so they are honed with a torque plate bolted down at head-bolt torque. An aluminum piston measured while still warm from the washer reads large, which makes the calculated clearance smaller than it really is.
05The other content areas
The A9 test has six content areas. Each has its own page of free questions:
The ASE A9 Light Vehicle 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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