Posted by Dave (Sussex UK) on August 29, 1998 at 03:29:20:

In Reply to: Replacing Plugs posted by SKA on August 27, 1998 at 08:09:57:

My 3.9 V8 gets used for off-roading and the engine gets very dirty so BEFORE extracting the plugs I use a high pressure cold water washer to clean all the debris away from the plug seats / surround (steam cleaner would be good if you have a local garage with one). A quick blast with an airline will remove any water / debris. After cleaning the plugs / replacing with new I use a squirt of WD 40 on the plug threads although copper-ease would be just as good (works at high temps). If the plugs are to be-used clean the threads with a BRASS wired wire brush - don't use steel wire brushes.
The reason for using lubrication is that steel into aluminium threads is bad news whether its a L-R cylinder head, washing machine or the space shuttle! DON'T use the wrench to start the thread use your fingers which are much more sensitive and STOP if the thread feels "tight". Do them up using your socket and extension bar with your fingers turning the threads, as far as the threads will go, then use the wrench to tighten BUT DON'T overtighten (maybe only 1/8th turn from finger tight to fully tight but be careful). The left hand bank in my NAS90 are very awkward - so be careful that the extension bar on the wrench is parallel to the threads because you need to "feel" how much torque you are applying or maybe use a universal joint on the wrench to also stop damage to the plugs / threads.
It's all good engineering practice - NO LUCK INVOLVED!

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