Well, I'll admit I don't know diddly about physics so I guess I have some reading to do.

But, I see it like this, and I guess that's wrong, as the aluminum expands the external dimensions get larger (however miniscule), as the dimensions get larger, the hole through the material can only get smaller. The expanding material makes the diameter of the opening smaller thus tighter. If the hole actually was increasing in size as the explained laws of physics suggest, then on a hot engine the plugs would actually be looser, not tighter, and the threads would not be damaged - contrary to real life.

OK, time to read.

EDIT: will have to wait till I can read the link at work as I don't have powerpoint.

__________________
Mike Tangas
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72

'02 CLK320 Cabriolet - wifey's mid-life crisis

2012 VW Jetta Sportwagon TDI...at least its a diesel

Non illegitemae carborundum.