Heavy Duty Equipment Technician (421A) — Red Seal

Performs common occupational skills

A technician will work under a raised excavator boom to replace a hydraulic line. Which action keeps the work area safe during the repair?

1. Rely on the hydraulic hold valves alone to keep the heavy boom raised in place
2. Leave the engine running the whole time so full hydraulic pressure stays available
3. Place a single plastic warning cone beside the open hydraulic line on the floor
4. Install a mechanical boom support or lower the boom to the ground first

A raised boom held only by hydraulics can drop if a line, seal, or valve fails, so a positive mechanical support or lowering the boom fully removes the crushing hazard before anyone works beneath it. Trusting hold valves leaves the load supported by the very system being opened. Leaving the engine running maintains pressure but does nothing to protect against a sudden loss of that pressure and adds running hazards. A cone marks an area but provides no physical protection against a falling boom. Mechanical support or grounding the boom is the recognized safe practice.

RSOS 2023 | A-1.02 Maintains safe work environment

Services, diagnoses and repairs engines and supporting systems

A cylinder compression test reads low, but when a small amount of oil is added through the injector bore and the test is repeated the reading rises noticeably. What does this wet test result point to?

1. Worn rings or cylinder bore allowing combustion gas past the piston
2. A leaking head gasket carrying compression between two adjacent cylinders in the block
3. A stuck-open exhaust valve leaking compression past the seat in that one cylinder
4. A cracked cylinder head leaking compression above the combustion chamber on that cylinder

Adding oil temporarily seals the gap between the rings and the bore. If compression jumps after the oil is added, the leak path is past the piston, pointing to worn rings or a worn bore. A leaking head gasket between cylinders would not be sealed by oil on the piston, so the reading would stay low. A stuck-open valve leaks at the valve seat, which oil on the piston cannot block. A cracked head also leaks above the piston, so the wet test would show little change, making ring or bore wear the clear conclusion.

RSOS 2023 | B-5.02 Diagnoses base engines

Services, diagnoses and repairs steering, suspension, brake and undercarriage systems, and wheel assemblies

A technician is replacing the steering pump on a grader. After installation, which step best protects the new pump from start-up damage?

1. Pre-fill the pump housing with clean hydraulic oil and prime the supply line before cranking
2. Start the engine and run it at high idle until the pump begins to move oil
3. Crank the engine in short bursts without starting it so the pump draws oil in gradually
4. Start the engine at low idle and cycle the steering lock to lock to bleed air from the circuit

A dry pump that spins without oil wears its internal surfaces within seconds because there is no lubricating film. Pre-filling the housing and priming the inlet ensures the pump has oil the instant it turns. Starting and waiting for oil to arrive runs the pump dry. Cranking in short bursts still turns the pump with no oil film until oil arrives. Cycling the steering at low idle bleeds air, but it is a later step and the pump still starts dry if it was not filled.

RSOS 2023 | C-13.01 Services steering systems