Spark Plug Replacement

Spark Plug Replacement

Here are some tips to follow when replacing a spark plug.

Every time a spark plug fires, the spark burns a few molecules of metal off the plug’s electrodes. Over time, this eats away the electrodes and rounds off their sharp edges. The erosion gradually increases the gap between the electrodes, which, in turn, increases the firing voltage required to generate a spark. Eventually, the point is reached where the ignition system fails to produce enough voltage and the plug misfires.

Misfires are bad news because they cause a noticeable loss of power and fuel economy, and a less obvious but very measurable increase in unburned hydrocarbon (HC) emissions. The catalytic converter can take care of the extra HC up to a point, but a steady misfire can make the converter overheat. If the converter gets too hot, it may suffer irreparable damage, resulting in a power-robbing exhaust restriction or a loss of efficiency (which will set a P0420 catalyst code).

SOME DISASSEMBLY REQUIRED

Modern engines tend to have the spark plugs placed as close to the combustion chamber as possible. With twin cams, long runner intakes and other obstacles, access to the spark plugs can be difficult. Take your time and make sure you bill the correct hourly rate.

INSPECT THE COILS

Coils shouldn’t have any visible damage, and the boot should be fully seated. While assembling coils to the engine, disregard the coil if you notice any visible damage like a cracked coil housing, broken anti-rotational tabs or a broken connector. Any damaged part could lead to a premature failure, and a poorly seated boot could lead to engine misfire.

Inspect the coils and keep them in order. They can help to eliminate any diagnostic variables if there is a problem after plug replacement.

THRU-BOLTS

Always apply the specified torque to the specified mounting thru-bolt. Loose thru-bolts could lead to failures under vibration. Overtightened thru-bolts could also lead to a cracked coil mounting ear and/or premature thru-bolt failure.

TORQUE AND ANTI-SEIZE

Always tighten plugs to OEM specifications. Overtightening plugs in aluminum heads will usually damage the threads in the cylinder head. Do not use anti-seize on plated plugs being installed in an aluminum head because anti-seize can change torque values. If the OEM doesn’t use anti-seize, you shouldn’t either.

anti-seize On modern aluminum heads can change torque values and cause the plugs to be over torqued.

Be careful to avoid creating a path of least resistance by inadvertently leaving a greasy fingerprint or chemical residue on the spark plug insulator.

GAPPING

For modern fine-wire spark plugs, don’t measure the gap because you could damage the center electrode. However, it’s still a good idea to inspect the new spark plugs for damage or defects. The majority of these plugs come pre-gapped from the factory.

On these types of plugs, bending the ground electrode(s) can alter the geometry and thermal performance of the electrodes to the point of causing a misfire.

On older applications, gapping may still be required. Gapping specifications can be found in the service information or emissions tag under the hood. Gapping specifications can also be found in electronic and paper catalogs.

Gap can be adjusted and measured on fine-wire spark plugs; just use the right tools and stay away from the center electrode.

Measuring the gap requires the right tools. A coil-style gap gauge will work for copper-core plugs. For fine-wire or precious metal plugs, a wire-type gauge is recommended.

If it is necessary to widen the gap, do so with a tool that pulls back only on the ground electrode without touching the center electrode or the porcelain. To close the gap on a plug, gently tap the plug, electrode first, on a hard surface.

With spark plugs lasting 100,000 miles, don’t skimp on the plug or the hours involved replacing them. Using less expensive plugs can lead to impaired-performance sooner.

You May Also Like

What Happened To Turbo Lag In Today’s Engines?

Yesterday’s turbo lag was eliminated thanks to years of development and a bit of clever engineering.

When I think of turbocharged engines, the first thing that comes to mind is turbo lag. Turbo lag is the time it takes for the turbocharger, or turbochargers, to spool up and generate boost pressure after the throttle pedal has been pushed down. Looking back just a decade or two, turbo lag seemed to be much more common, and more severe. It seemed like you could put the pedal to the metal, count to five, check your watch, THEN you’d finally feel the boost kick in.

Understanding Engine Timing – Chains, Gears and Belts

Perfect timing is critical in the performance world, and now, it’s required by your regular customers too.

Cartridge Oil Filters

Mistakes made can result in costly comebacks.

Aging Plastic Intake Components May Cause Leaks

BMW valve covers and intake manifolds made of plastic are susceptible to warpage and gasket failure.

Five Spark Plug Service And Replacement Tips

Most articles will tell you to use a torque wrench, but they never explain why.

Other Posts

Do You Know The Cause Of A No-Spark Condition?

A no-spark condition could be the result of communication errors or missing data from a dead module.

Parts and Artificial Intelligence

In the past 25 years, things have changed with the Internet.

Dayco Expands H-D Belt Kit Line

Dayco says six new SKUs cover hundreds of thousands of Class 8 fleet vehicles on the road today.

Streamlight Launches Stinger Color-Rite Light

Flashlight allows users to better see the color spectrum under low light conditions.