Tools & supplies
- New spark plugs (correct part number & heat range for your BT-50/Ranger engine)
- Spark plug socket (6- or 12-point) sized for the plug hex (commonly 5/8" (16mm) or 13/16" (21mm)) with rubber or magnetic insert
- 3/8" drive ratchet, 3/8" drive extensions (short ~50mm + 125–250mm), universal joint
- Torque wrench (range to cover 10–50 Nm)
- Feeler gauge or preset gap tool
- Dielectric grease (small amount) and/or anti-seize (only if manufacturer recommends)
- Compressed air or shop vacuum, shop rags
- Small pick or flat screwdriver (for O-ring removal)
- Safety glasses, nitrile or mechanic gloves
- Battery terminal puller or wrench (for disconnect)
- Optional: penetrating spray, replacement ignition coil boots / O-rings

Safety precautions
- Work with the engine cool to avoid burns. If the engine was running, let it cool until warm/cool.
- Disconnect negative battery terminal before starting to avoid accidental cranking.
- Wear safety glasses. Keep clear of moving parts and hot surfaces.
- Keep fuel vapors away (no open flames/sparks).
- Clean debris from around plug wells before removal to prevent foreign material dropping into combustion chamber.

Preparation
1. Confirm correct plug part number, thread size, reach, and gap spec for your engine (consult service manual). Common gap for many Ford petrol engines: 0.7–0.8 mm (0.028–0.032 in) — verify.
2. Inspect replacement plugs; if pre-coated with anti-seize, do NOT add more. If bare threads, apply a very light film of anti-seize. Do not overdo it (will affect torque).
3. Set plug gaps with feeler gauge to spec before fitting.

Step-by-step procedure
1. Park on level ground, engage handbrake, place wheel chocks. Disconnect negative battery terminal.
2. Remove engine covers or intake components necessary for access to coils/plugs.
3. Blow compressed air or vacuum around each spark plug well to remove dust and debris.
4. Identify ignition coil(s) or plug wires:
- Coil-on-plug (most modern BT-50/Rangers): you’ll remove one coil at a time.
- Older wire-and-plug systems: remove and replace one wire/plug at a time to keep firing order correct.
5. For coil-on-plug:
a. Disconnect the coil electrical connector (depress tab) and unbolt the coil retaining bolt(s).
b. Pull the coil straight up. If stuck, twist gently — do not pry on the wiring.
c. Inspect coil boot O-ring/seal; replace if cracked.
6. Remove the old plug:
a. Fit the spark plug socket (with rubber insert) on the extension. Place over the plug and turn with ratchet counter-clockwise.
b. Extract the plug using the socket/extension; the rubber/magnet will hold it.
c. Inspect the old plug for color and deposits (normal: tan/light brown; heavy carbon, wet oil, or white deposits indicate issues).
7. Install new plug:
a. Start the plug by hand into the cylinder head to avoid cross-threading. Use only fingers until fully engaged.
b. Fit the socket (with short extension). If you used any longer universal joints, keep them minimal — torque accuracy drops with long or angled extensions. Best practice: torque with short extension inline.
c. Tighten finger-tight, then torque to specification. Typical torque ranges: M12 plugs ~20–28 Nm (15–21 lb-ft); M14 plugs ~28–40 Nm (21–30 lb-ft). Verify exact spec in the manual.
8. Reinstall coil:
a. Apply a small smear of dielectric grease inside the coil boot (on the rubber) if recommended.
b. Push coil straight onto the plug until seated. Reinstall and torque the coil retaining bolt to spec (commonly ~8–12 Nm).
c. Reconnect the electrical connector.
9. Repeat steps 5–8 for each cylinder, working one coil/plug at a time.
10. Reinstall any removed engine covers/intake parts. Reconnect negative battery terminal.
11. Start engine and confirm smooth idle. Clear any diagnostic trouble codes if present and test-drive.

How tools are used (brief)
- Spark plug socket: holds plug with rubber/magnet; use an extension to reach down into plug well. Use the correct socket size to avoid rounding the hex.
- Torque wrench: final tightening to specified torque — attach with a short, direct extension; avoid angled adapters for final torque.
- Feeler gauge: measure gap. Slide appropriate thickness blade between electrodes until correct resistance is felt.
- Compressed air: remove debris around wells before unplugging.

Replacement parts & consumables
- New spark plugs (required)
- Coil boots / O-rings (inspect and replace if degraded)
- Dielectric grease (small amount)
- Anti-seize only if manufacturer recommends for your plug type
- Replacement ignition coils if damaged or failing

Common pitfalls & how to avoid them
- Cross-threading plugs: always start by hand.
- Over-torquing (or under-torquing): use a torque wrench; be careful if anti-seize was used (it lowers friction and can lead to over-torque).
- Using wrong plug reach/heat range: will damage engine or cause misfires—use exact OEM or approved equivalent.
- Not cleaning plug wells: debris can fall into cylinders causing damage — blow out wells first.
- Breaking the ceramic insulator: avoid prying or excessive side load when removing/installing.
- Applying too much anti-seize: leads to over-torque. Most modern plugs are plated and do not need it.
- Replacing multiple plugs at once without marking wires on older systems: do one at a time or mark wires to preserve firing order.
- Using long or angled adapters for final torque: torque readings become inaccurate. Use a short straight extension for final torqueing.

Quick inspection guide (what old plug tells you)
- Light tan: normal
- Black, dry soot: rich mixture/weak ignition
- Oily wet plug: oil control (PCV, valve seals) issue
- White, blistered porcelain: overly lean or detonation
- Heavy electrode wear: overdue for replacement or incorrect heat range

Done.
rteeqp73

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