Timing, plugs, ignition

Six procedures. Guided first attempts at plug servicing are in PP-H Hands-on.

Everything here happens near a propeller. PP-A Procedure 0 applies to every step.

Procedure 0 — Ground the magnetos (R3)

1. Ignition off, mixture idle cut-off, master off, chocks in.
2. Disconnect the P-leads at the magnetos and ground them, or fit the shorting devices the manual specifies.
3. Confirm by the manual's method that both magnetos are grounded.
4. Only then treat the engine as safe to turn — and still move the propeller as though it is not (PP-H Concepts §1).

Check — point at both grounded P-leads. Switch position is not evidence.

Procedure 1 — Set magneto internal timing (S1)

1. Remove the magneto per the manual, or set it on the bench.
2. Rotate to the E-gap position using the manual's method — a timing pin, an index mark, or a specified rotation past the neutral position.
3. Adjust the breaker points so they just open at that position, using a timing light or a buzz box.
4. Check the point gap at full open against specification.
5. Check cam follower condition and point face condition.

Check — rotate through and confirm the points open at the same position on the next cycle. A one-off setting that does not repeat means a worn cam, a loose follower or a slipping adjustment.

Procedure 2 — Time the magneto to the engine (S2)

1. Locate top dead center on the compression stroke, number one cylinder (PP-A Procedure 1).
2. Rotate back and then forward to the specified degrees before top dead center, approaching in the direction of rotation to take up backlash.
3. Fit the magneto with its internal timing set (Procedure 1) and rotated to the firing position.
4. Adjust until the points just open at the engine timing position, using a timing light on both magnetos.
5. Tighten the clamps and re-check — tightening moves it.
6. Check both magnetos fire at the specified position.
7. Connect the P-leads, and confirm the magnetos ground when switched off.

Check — re-check after tightening, every time. Timing set and then clamped is not timing; the clamp moves the magneto.

Failure — timing on the wrong top dead center. The piston reaches TDC twice per cycle (PP-H Concepts §3).

Procedure 3 — Service spark plugs (S3, S11)

1. Procedure 0.
2. Remove leads carefully — pull the connector, not the lead.
3. Remove plugs, keeping them in cylinder order. The order is the diagnostic (PP-H Concepts §4).
4. Read them: color, deposits, electrode wear, and any that differ from the rest.
5. Clean by the approved method, without damaging the electrodes or the insulator nose.
6. Gap to the specification, adjusting the correct electrode by the correct method.
7. Test where a tester is available.
8. Fit new gaskets, anti-seize on the threads only where the manual specifies and never on the electrode end, and torque to specification.
9. Rotate the plugs through cylinders per the manual to even out wear.

Check — lay them out in cylinder order before cleaning anything. One plug that looks different from the other seven is telling you about that cylinder, and once cleaned that information is gone.

Failure — over-torquing a plug. It distorts the plug and can damage the helicoil or the head threads (GEN-E Concepts §1).

Procedure 4 — Inspect an ignition harness (S7)

1. Inspect leads for chafe, hardening, cracking and heat damage, especially where they pass near exhaust.
2. Inspect connectors and springs at both ends.
3. Check security and routing — clear of hot sections and moving parts.
4. Where the manual permits, test insulation resistance of the leads.
5. Check the distributor block for cracks, tracking and moisture.

Check — look for carbon tracking in the distributor block and at the connectors. It is a fine black line, it is a conductive path, and it produces a misfire that comes and goes with humidity.

Procedure 5 — Inspect an impulse coupling (S8)

1. Procedure 0.
2. Rotate the engine slowly by hand in the direction of rotation and listen for the click on each affected magneto.
3. Check for cracks, wear and free movement of the pawls where accessible per the manual.
4. Confirm the coupling releases at the specified speed by the manual's method.

Check — the click is the check. No click means the coupling is not engaging, the magneto is not retarding for start, and the engine may kick back (PP-H Concepts §6).

Procedure 6 — Inspect turbine igniters (S14, S17, R2)

1. Switch off, wait the specified discharge time, and follow the manual's discharge procedure. The capacitor holds lethal energy (PP-H Concepts §5).
2. Disconnect the igniter lead, capping it.
3. Remove the igniter, handling it as brittle.
4. Inspect the tip for erosion against the manual's limits, and the insulator for cracks.
5. Inspect the lead for damage and the connector for security.
6. Install with new seals, torqued per the manual.

Check — state the discharge time and confirm it has elapsed. "It's been a while" is not a discharge procedure.

The checks, collected

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