CEM Technical Skills & Application 5 — Questions and Answers
Question 1: A CEM is evaluating whether to rebuild or replace a failed diesel engine. The rebuild quote is 65% of the replacement cost. What additional factor is MOST critical to this decision?
- Engine serial number and manufacturing date
- Remaining service life of the machine relative to rebuilt engine warranty (Correct answer)
- Brand of the replacement engine
- Current fuel cost per gallon on the project
Correct answer: Remaining service life of the machine relative to rebuilt engine warranty
If the machine has limited remaining economic life, investing 65% of a new engine cost in a rebuild may not be recoverable before the machine is retired.
Question 2: When calibrating a motor grader blade cross-slope using an indicate system, which sensor input provides the primary cross-slope reference?
- GPS elevation from the left mast antenna only
- An in-cab pendulum or MEMS-based slope sensor mounted perpendicular to the blade (Correct answer)
- The circle drive gear position encoder
- Engine speed feedback from the ECM
Correct answer: An in-cab pendulum or MEMS-based slope sensor mounted perpendicular to the blade
Cross-slope control relies on an accelerometer or MEMS slope sensor measuring blade tilt angle relative to gravity perpendicular to the direction of travel.
Question 3: Which test BEST determines whether an engine's turbocharger is delivering adequate boost pressure for its rated output?
- Observing exhaust smoke color under load
- Recording boost pressure under load with a calibrated gauge or scan tool and comparing to OEM specification (Correct answer)
- Measuring compressor wheel axial endplay only
- Checking the air filter restriction indicator
Correct answer: Recording boost pressure under load with a calibrated gauge or scan tool and comparing to OEM specification
Comparing measured boost pressure against the OEM specification under rated load is the definitive test for turbocharger performance adequacy.
Question 4: A CEM finds that a compactor's vibratory system runs at only 75% of the specified frequency. The most likely cause in an eccentric-weight vibratory system is:
- Hydraulic motor case drain restriction causing over-pressurization and speed reduction (Correct answer)
- Worn eccentric weight bearings increasing rotational friction and reducing speed
- Incorrect eccentric weight mass
- Engine overspeed condition
Correct answer: Hydraulic motor case drain restriction causing over-pressurization and speed reduction
A restricted case drain line increases back-pressure on the hydraulic motor, acting as a braking force that reduces shaft speed below specification.
Question 5: Which ANSI/SAE standard governs the rated operating capacity (ROC) of compact construction equipment such as skid steer loaders?
- ISO 9001 Quality Management
- SAE J818 / ANSI/ITSDF B56 rated load at 35% of tipping load (Correct answer)
- OSHA 1926 Subpart CC
- ASME B30.5 Mobile and Locomotive Cranes
Correct answer: SAE J818 / ANSI/ITSDF B56 rated load at 35% of tipping load
SAE J818 establishes that the ROC for skid steer loaders is 35% of the static tipping load, providing the rated capacity operators and planners must not exceed.
Question 6: A diesel engine experiences white smoke at startup that clears within two minutes of warm-up. The MOST likely cause is:
- Worn piston rings allowing oil to enter the combustion chamber
- Incomplete combustion of fuel due to low cylinder temperature before warm-up, producing unburned fuel mist (Correct answer)
- Coolant entering combustion through a cracked head
- Clogged diesel particulate filter (DPF)
Correct answer: Incomplete combustion of fuel due to low cylinder temperature before warm-up, producing unburned fuel mist
White smoke that clears after warm-up is caused by unburned fuel condensing in cool exhaust; once cylinders reach operating temperature, combustion is complete and smoke stops.
Question 7: When selecting replacement wire rope for a crane, which factor has the GREATEST influence on fatigue life when the rope must operate over small-diameter sheaves?
- Rope diameter
- Wire count per strand (more wires = greater flexibility and fatigue life) (Correct answer)
- Core type (fiber vs. independent wire rope core)
- Rope lay length
Correct answer: Wire count per strand (more wires = greater flexibility and fatigue life)
Ropes with more, thinner wires per strand distribute bending stress over a larger number of wires, significantly extending fatigue life when operating over small-radius sheaves.
CEM Technical Skills & Application 5
A CEM is evaluating whether to rebuild or replace a failed diesel engine.
The rebuild quote is 65% of the replacement cost.
What additional factor is MOST critical to this decision?