Spark Plug torque

[Cadmandu]

I read that a 14 mm spark plug in an aluminum head should be torqued from 18 to 22 ft/lb. That sounds really high to me any comments?

[lragan]

Don't know about the 14 mm, but the shop manual for my 3rd gen calls for 9 ft-lbs on the 10mm plug.  18-22 ft-lbs would imply more than a square law scaling in thread diameter --

14mm/10mm = 1.4

1.4^2 = 1.96

1.96 * 9 ft-lbs = 17.64 ft-lbs

Some of you mechanical whizzes can tell us how torque should scale with thread diameter....

[Cannon]

I dont know about torque but the plug maufaturers often describe the installation like "hand thigten and then do an extra 1/4 to 1/2 turn". The washer/gasket is usually of the collapsible type, som when installing previously used plugs the extra turns after handtightening should be reduced.