I had the same question cause I was concerned about leaks. I was told to wait until engine was cold. This works at home but if you are on a club tour you can't wait to swap out a dist assy. I finally settled on an extra long bolt with one nut properly tightened down on the head, put the cable clamp on the nut and hold it down with another nut. Then you can change the dist on the side of the road with the engine hot. OR don't use the clamp at all.