Hey Brenton, One other point when changing out the plugs on a 928 is to use a good blast of compressed air to blow out the spark plug holes really well. I always take plug removal in two steps. First blow out any crud that is just laying around the bottom of the recessed areas. A cheap spray can of brake/carburetor cleaner can help if needed for oil removal. Then loosen each spark plug a few turns to help breakup any remaining encrusted or hardened oxidization that may have built up around the base of each sparkplug and blow it all out again. If you are not careful because of the vertical angle of the plugs on a 928, chunks of grit can easily fall down into the cylinders and damage the rings, piston skirt or cylinder walls.
I use a very light coating of anti-seize on the threads of the new plugs. This helps to prevent the plug threads from galling during the next tune-up process and can reduce the potential for electrolysis (reaction between dissimilar metals - aluminum head / steel plug base). The anti-seize paste is a conglomerate specifically formulated to help aluminum and steel cohabitate next to each other. (By the way, the anti-seize step is often vigorously debated because in theory, if used in excessive amounts, could potentially hinder current travel between the base of the plug and the grounded cylinder head). Personally, I've never had any indication of a problem.
Don’t over torque the plugs - we are talking aluminum here. I’ve had to help pull a couple of heads because the owners were a little too enthusiastic with the break over bar. Also, you might consider installing a set of platinum tip plugs simply because they last so much longer than most others. If the engine is in good running condition, this type of plug can last for years with only a minor cleaning once a year.
Good Luck, Michael
