Working on a reciprocating engine

Six procedures. Procedure 0 applies to every one of them and to everything else in Powerplant.

Procedure 0 — Before you touch the propeller (R1)

1. Magnetos off, mixture idle cut-off, throttle closed, master off.
2. Where the work requires certainty, disconnect and ground the P-leads at the magnetos.
3. Chocks in, brakes set.
4. Call clear, and confirm nobody is in the propeller arc.
5. Move the blade in the direction of rotation, standing clear of the arc, with your body never where the blade will travel.

Check — say "the propeller is live" out loud before you touch it. That is not superstition; it is the only defense against the switch that says OFF and is not (PP-A Concepts §1).

Procedure 1 — Locate top dead center, number one cylinder (S8)

1. Identify number one cylinder from the engine data — the numbering convention varies by manufacturer and it is not always obvious.
2. Remove a spark plug from that cylinder.
3. Rotate in the direction of rotation (Procedure 0) while feeling or listening for compression, which identifies the compression stroke rather than the exhaust stroke.
4. Use a TDC indicator, timing pin or piston-stop tool per the manual to find the exact position.
5. Confirm against the timing marks on the ring gear or accessory case.

Check — you must be on the compression stroke. The piston reaches top dead center twice per cycle; the other one is wrong for timing purposes, and everything downstream inherits the error.

Procedure 2 — Cylinder assembly inspection (S1)

1. Clean without damaging surfaces — no wire brushing of aluminum (GEN-G Procedures Procedure 2).
2. Inspect the barrel bore: scoring, glazing, wear, corrosion, and check for out-of-round and taper by measurement (GEN-E Procedures Procedure 2).
3. Inspect valves and seats: burning, pitting, recession, guide wear.
4. Inspect the head: cracks — especially between valve seats and around plug bosses — and fin damage.
5. Inspect studs and threads.
6. Measure everything against the manual's limits and record.

Check — measure, do not judge. Bore, valve guide clearance and stem clearance all have numbers, and eye assessment passes cylinders that are out of limits.

Procedure 3 — Install a piston and wrist pin (S3)

1. Confirm piston part number, size and orientation. Pistons are directional — there is a front, and installing one backwards changes valve clearance.
2. Install rings correctly: right ring in the right groove, gaps staggered per the manual, and the marked side up.
3. Lubricate per the manual.
4. Fit the wrist pin and its retention — circlips fully seated in their grooves, or plugs as specified.
5. Compress the rings with a ring compressor and enter the barrel squarely.

Check — tug the circlips. A circlip not fully seated comes out in service and the wrist pin destroys the barrel. It is a two-second check for a catastrophic failure.

Procedure 4 — Install a cylinder (S9)

1. Confirm the base seal or O-ring is correct and correctly positioned.
2. Enter the cylinder squarely with the rings compressed, without turning the crankshaft.
3. Fit the hold-down hardware and torque in the manual's sequence, in the manual's stages — not round the circle, and not in one pass (PP-A Concepts §6).
4. Re-torque where the manual requires it.
5. Connect pushrods, rockers and induction, and set valve clearance where the engine requires it.
6. Rotate the engine by hand through two full cycles before any attempt to start.

Check — rotate it by hand, fully, twice. Any binding, tight spot or unusual resistance means something is wrong, and finding it by hand costs nothing while finding it on the starter costs an engine.

Procedure 5 — Operate and troubleshoot an engine (S2, R2)

1. Everything in GEN-F Procedures Procedure 7 — checklist, area brief, clear call.
2. Note ambient conditions and compute density altitude (GEN-J Procedures Procedure 3). Without it, no performance judgment is possible.
3. Start per the checklist, monitor oil pressure immediately, and shut down at once if it does not appear within the specified time.
4. Warm to the specified temperature before any power check.
5. Perform the checks the manual specifies: magneto drop, idle, mixture rise, static RPM, temperatures and pressures.
6. Compare against book figures corrected for the day.
7. Shut down per the checklist.

Check — correct for density altitude before judging any figure. An engine reaching book static RPM on a hot day at elevation is performing well above book, and one that misses it may be entirely serviceable (GEN-J Concepts §5).

Failure — condemning a good engine, or passing a bad one, on uncorrected numbers.

The checks, collected

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