MG T-Series ArchiveMGT-SERIESMG T-Series

Servicing · Ignition

Changing the spark plugs

Plugs are the simplest tune-up job on the car — and one of the best windows into engine health you have.

Why and how often

Plugs are the simplest tune-up job and a good window into engine health — check/clean at each service and renew as needed. “Reading” the plugs tells you a lot; sooty-black plugs mean an over-rich mixture (see the workshop case study for a real example).

Step by step

  1. 01

    Work on a cool engine

    Work on a COOL engine — hot alloy heads are easily damaged.

  2. 02

    Remove the leads in firing order

    Pull each plug lead by the connector, not the wire, one cylinder at a time so leads return in firing order (1-3-4-2).

  3. 03

    Clear debris and undo the plugs

    Brush or blow debris from each plug well so nothing drops into the cylinder. Undo each plug with the correct spark-plug spanner.

  4. 04

    Read the old plugs

    Read the old plugs: light tan/grey = healthy; black and sooty = rich mixture or weak spark; oily = oil getting past; white/blistered = running too hot or weak.

  5. 05

    Gap the new plugs

    Gap the new (or cleaned) plugs with a feeler gauge to 0.025" (points), bending only the side electrode gently. A little anti-seize on the threads (sparingly, away from the electrode) eases future removal from alloy.

  6. 06

    Start each plug by hand

    Start each plug BY HAND to avoid cross-threading the alloy head, then nip up — seat plus about a quarter-turn. Refit the lead.

  7. 07

    Start up and re-check

    Start up and check it runs evenly; if you disturbed anything, re-check idle/timing (see Tuning).

Read next

This guide is a general introduction and is not a substitute for the official Workshop Manual for your car.