Reciprocating Engine Overhaul Flashcards

During a reciprocating engine overhaul, a Magnaflux inspection is performed on the steel crankshaft. What is the primary purpose of this inspection?

Answer: To detect surface and near-surface cracks or discontinuities.

Magnaflux, or Magnetic Particle Inspection (MPI), is a nondestructive testing method used to find surface and slightly subsurface discontinuities in ferromagnetic materials like steel. The process involves magnetizing the part and applying iron particles, which will gather at any magnetic flux leakage fields caused by cracks, clearly indicating the flaw.

A technician is assembling a cylinder onto a reciprocating engine and is preparing to torque the cylinder base nuts. According to most manufacturer's instructions, what is the proper general procedure for torquing these nuts?

Answer: Torque all nuts to half the specified value in sequence, then to the final value in the same sequence.

Proper procedure for torquing cylinder base nuts typically involves a multi-step process to ensure even pressure and prevent warping. The nuts are first torqued to an intermediate value (often half of the final spec) in a specified sequence, and then the process is repeated to bring them to the final torque value. This ensures the cylinder is seated correctly and stress is evenly distributed.

After grinding the valves and valve seats in a cylinder head, what is the purpose of the lapping procedure that follows?

Answer: To ensure a perfect, gas-tight seal between the valve face and the seat.

Valve lapping uses a special abrasive paste applied between the valve face and its seat. The valve is then rotated against the seat, which creates a fine, smooth, and perfectly matched sealing surface. This ensures maximum compression and prevents the leakage of combustion gases.

When installing new piston rings, a technician notes that one of the compression rings has a small dot or the word "TOP" marked on one side. How should this ring be oriented in the piston groove?

Answer: The mark should be positioned facing the top of the piston (the crown).

Many piston rings are directional and have a specific profile or taper to function correctly for sealing and oil control. A mark, such as a dot or the word "TOP," indicates the side of the ring that must face upwards, toward the crown of the piston. Installing a directional ring upside down can lead to excessive oil consumption and poor compression.

A technician is inspecting a connecting rod from a recently disassembled engine. Which of the following conditions would be cause for mandatory rejection of the part?

Answer: The connecting rod exhibits a slight twist or bend beyond serviceable limits.

The straightness of a connecting rod is critical. Any bend or twist beyond the manufacturer's specified limits will cause misalignment of the piston and bearings, leading to uneven wear, excessive friction, and ultimately catastrophic engine failure. Such a part cannot be repaired and must be rejected.

An engine has been overhauled according to the manufacturer's manual using a combination of new parts and used parts that conform to "serviceable limits." How is the total time in service (TIS) on the engine logbook affected?

Answer: A new logbook is started, and the old time is archived.

According to FAA guidance, when an engine is overhauled to serviceable limits (as opposed to being rebuilt by the manufacturer to new limits), the total time on the engine and its records continues. Only a "rebuilt" engine, which is brought to the same tolerances and limits as a new engine by the manufacturer, can be granted zero time.