boxkite

I have a old 1987 F150 with a 4.9l (300ci) inline 6. Here lately the spark plugs have been coming loose. They don't seem to come loose while I'm driving. But after I shut it down. The next time I go to drive. one are two of any giving spark plug/s might be loose. As if they're loosing up as the engine cools.
Last fall I put a set of Autolite platinum AP 5125 in it. I had no problem with them coming loose all winter. But now that summers here (about a week ago) they started coming loose. So I went out and got a set of Motorcraft (O.E style) sp-435 BSF44C copper spark plugs, cap & rotor and some new plug wires. Hoping this would fix the problem. It did not. Maybe I'm not getting them torque down hard enough. I will try and torque them down harder today. But if it's not a torque issue. What else could be causing this to happen?
Thank you.

Marc D

Try using this torque spec guide. Depending on the style of plug and the head material it will give you an idea of how many foot pounds of torque you need. Use a 3/8" torque wrench not a stepped down 1/2" for better control. Also use some copper anti-seize on the threads before you install the plugs. http://www.ngksparkplugs.com/techinf...stallation.asp