And the simple engineering involved is that cylindrical clearances increase with temperature, thereby reducing the opportunity for binding (being galling or whatever). Furthermore, the yield temperature (i.e. the point at which the material plastically deforms) of the aluminum alloys in the heads is far greater than the 'blistering' 250 F that may be there by the time you work the head. The reduction in material strength from 100 degrees to 250 degrees in said alloys will not be of concern. In other words, there are good technical reasons to support his experience based feedback which I will likely utilize when it is my turn to change plugs. My experience is that manuals, although good, are not perfect. This is clearly a design flaw in Ford's engine, likely the sme members of the team that designed this head evolutuion were involved in the manual text. If so, they would not be fully cognizant of the issue or we would not be having this dialogue. I always sought reviews of savvy field techs, mechanics, etc. in my designs before issue since they have a better field (i.e. experience based) perspective than I. In several instances, I received feedback for things I had not considered which improved the output.
