What is the correct torque setting for a Spark Plug?

posted on 28 August 2014 | posted in General info

What is the correct torque setting for a Spark Plug?

The correct torque setting for a spark plug will depend upon its thread size. For example a standard 14mm spark plug used on most motorbikes & scooters (for example those starting with a "B" in NGK's range such as a B8ES ), the correct torque setting is 25 to 30 Nm. Whereas for the larger sized 18mm spark plug thread the correct tightening torque is 35 to 40 Nm and for the smaller 12mm thread it is 15 to 20 Nm.

In all cases, the spark plug should be initially tightened by hand in order to ensure that the thread is not damaged. A good tip is to have a length of rubber tube that will slip over the end of the plug and use this to insert and initially tighten the spark plug up, perfect for where additional reach is required.

If you insert a spark plug using a socket to start with, this is likely to result in the thread being damaged or stripped, as it is more difficult to feel whether the thread is tightening up correctly or mis-threaded. It is very unlikely to apply too much force resulting in thread stripping when tightening by hand.

Alternative option when a torque wrench is not available.

An alternative to using a torque wrench is to tighten the plug as tight as possible by hand and then tighten it an extra 1/2 to 2/3 of a turn (180 to 230°) using a socket to squash the washer. Be careful when reusing spark plugs as the washer will already have been squashed during the original fitting, therefore the plug should only be tightened an extra 1/12 of a turn (30°) beyond hand-tight using a socket.