Spark Plug Maintenance

First, what kind of plugs should you use? From 70,000 miles of experience, I like Champions, and contrary to what you may read elsewhere, their cut threads will not damage a BMW if you install them carefully. Champion and other plug manufacturers all put out handbooks on how to inspect used plugs, whether to use a hotter or colder plug, etc., so I’ll skip those discussions here. I use Champion N6Y plugs and my driving doesn’t involve a lot of stop-and-go, city-type routes. I clean and re-gap plugs every 5,000 miles and replace them every 10,000. Also, by watching for specials I never pay more than 60 a plug.

Tools needed are:

  • Spark plug wrench
  • 2 inch ratchet extension
  • Ratchet handle
  • Wire feeler gauge or leaf gauge.
  • A wrench with the rubber insert that holds the plug is best; you can also use the tools from your car’s tool kit, which should include the required leaf gauge.

You will also need a tube of powdered graphite – all available at hardware and auto parts stores. Before starting the job, be sure engine is cold.

  1. Open and put a protective cloth on fender. Pull off the spark plug connectors, which are attached to the plugs with spring clips inside the large end of the connector. Inspect connectors for breakage (the large ends split easily, so I have taped all mine with electrical tape).
  2. Place spark plug wrench over the most accessible plug (don’t start loosening the plug. If you can’t get it to start, don’t force it but consult an experienced mechanic (yet this has never happened to me). As the plug loosens, turn the plug wrench by hand until plug is
    free. Be careful not to drop plug or you’ll break the ceramic insulator.
  3. If you plan to reuse the plugs, scrape off the crud with a metal or plastic scraper (don’t use a wire brush), and file the electrodes flat. All plugs, new or used, must be gapped to the specs in your owner’s manual, given in both metric (like 0.60 mm) or inches (0.024″) so you can use either type of gauge. Bend the L-shaped part of plug until you can just pull the correct wire gauge through, or until a leaf gauge just slides back and forth.
  4. Coat the plug threads with powdered graphite, then replace all plugs and start tightening by hand. This is critical; if you force a plug in and it isn’t seated right, you can ruin the threads inside the head (this is called cross-threading”). Screw then in as far as you can by hand, then apply wrench; tighten them only enough to secure them or you’ll have trouble getting them out the next time (professional mechanics use a torque wrench for this). Reconnect the plug connectors after first making sure they’re securely connected to the spark plug wires. Be sure to get the right connector on the right plug.

All this should take less than one hour and you’ll notice a marked improvement in performance.

Author: Richard 0. Neville


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