[914GOD]

The different thermal expansion rates of steel and aluminum did not have any effect on the tightness of your bolted joint....it was loose to begin with!

The joint should be as loose as it is going to get when it is cold. As the thing heats up the metal expands (steel and aluminium) and the joint always gets tighter. If the bolt where aluminum and the flange where steel this would be a different story as Al expands more than steel, but in this case, it was loose to start with.

By the way, tightening the bolts directly on the aluminium flange very well would keep them tight...because they are dug in to the aluminum flange, not for any thermal expansion reasons.

Hope this clears things up....

Sean