[cmonref]

I think Zeke is right -- the chains tighten as the engine warms up. The cylinders lengthen with heat (remember when dilavar studs were wonderful 'cuz they had the same thermal expansion characteristics as the cylinders?) This moves the cams farther away from the engine centerline. I have not seen anyone put a number on this expansion, but it is touted as the need for chain tensioners that can handle this variable dimension.