[olddog]

I did the autopsy on my son's 4.6 DOHC Lincoln after a broken valve spring dropped an exhaust valve. I was impressed with the guides that tension the chain and keep it from oscillating or vibrating. They obviously did not want the chain to have the slightest whipping action. I was also amazed that the plastic material looked new after 120K miles.

If you think about it, a slight whipping action in a chain would cause the distance of chain between the sprockets to increase. The shortest distance between any two points is a straight line, and a squiggly line is always longer.

The old books talk about chain stretch on the old cammers causing a timing difference in the two cams. I suspect the long unsupported chains whipping also contribute. On that long of a chain I'm sure there is length change do to thermal expansion of engine and chains. That has to have an impact as well. Perhaps a good hard look at the Modular design would inspire some design improvements for the old cammer.

My memory is that it is one long chain going from center cam, to left head to right head and back to the center cam. Maybe it was the crank, but I think it is the center cam. Anyway a short chain from the center cam to one head and another chain going to the other head would seem to solve a lot of problems.