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Inside Bikes

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Replacing or checking spark plugs is a feature of most bike services. It’s highly recommended to use a proper spark plug socket (make sure it’s the right size!) with a foam insert, as this protects the upper, porcelain part of the plug.


Cracking the porcelain, as you can with a normal deep socket, ruins the plug, and porcelain chips fall to the base of the plug where they could get into the engine and damage it after the plug comes out. If the plug’s very tight, try again when the engines hot as this often loosens up stubborn ones. The foam insert will also hold the plug when you lift it out, saving you from burnt fingers.


When replacing a plug it’s very important not to overtighten it, or you’ll damage the thread in the cylinder head. Your manual should provide torque settings but if not, or if there isn’t room for a torque wrench, tighten a new plug no more than half a turn after the first resistance, and a re-used one (the washer of which will already be partly compressed) only a further quarter turn.

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