Make sure that the spark plug’s thread reach is actually appropriate for your engine. Tighten the spark plug finger-tight until the gasket reaches the cylinder head, then use a spark plug wrench to tighten another 12 – 23 turns.

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How can you tell if a spark plug is properly tightened?

The majority of plugs have a gasket and fit into an aluminum head. Tighten these until they are snug, then turn them another 1/4 turn. You will feel the gasket collapse and it will become more difficult to turn in. This is typically around 20 ftlbs of torque, but many engines lack the space to accommodate a torque wrench, so you must rely on feel alone.

What happens if the spark plug is not properly tightened?

If the spark plug is not properly tightened, it will work its way out of the hole and most likely damage the threads on its way out. Cross threading a spark plug will damage both the plug and the threads in the head. A reamer thread tool can sometimes be used to repair the head. Alternatively, the head may need to be removed to be repaired.

Is a torque wrench really necessary for spark plugs?

Spark plugs should be torqued according to the manufacturer’s recommendations. However, the plugs can be satisfactorily tightened without the use of a torque wrench.

When changing spark plugs, should the engine be hot or cold?

Installing a spark plug while the engine is hot can cause the torque specification to change. When installing a spark plug while the engine is hot, the torque specification and how the threads on the engine and spark plug interact can change.

Do you lubricate new spark plugs?

NGK does not recommend applying lubricant such as copper grease to spark plug threads because it reduces frictional forces at the thread faces. It is critical not to overtighten or undertighten spark plugs during installation. Overtightening can cause spark plug distortion and breakage.

With a torque wrench, how tight should spark plugs be?

To avoid over- or under-tightening, most spark plugs are tightened between 8 and 40 Nm and should be installed to the manufacturer’s specified torque setting using a torque wrench. The larger the thread size of the spark plug, the more tightening is usually required.