The block is a 1977 from an F150. I've had it since new. Had new cam bearings put in, the mains were not align honed or bored. Replaced factory timing set (gears and chain) with a Cloyes True Roller (I think they now call them Original True Roller). This is the set used with a 1-piece fuel pump eccentric ... the original used a 2-piece fuel pump eccentric (I've changed the eccentric). The factory set was resonably tight on both sides ... and no, I don't have it any longer for comparison purposes.

The Cloyes set is designed for a crank to cam CL distance of from 4.802-4.804. The next undersize set is designed for a maximum CL distance of 4.799. My measured CL distance is 4.8005 (not a misprint).

The concern is that there is visible slack in the chain on one side (the other side is tight), and a rough measurement (gear to gear with a straightedge) when the chain is pushed in is around 1/4" to 3/8". Note: While the slack is visible, it's not like it's hanging ... and to get the measurement, we had to pull the chain in tight.

Cloyes says the change should be snug on both sides. They also don't recommend using the undersize chain set ... feel that it will lead to premature bearing wear.

I don't know what the factory CL distance is, but I'm assuming that the Cloyes 4.802-4.804 range is correct. That said, where have lost the .0.035"??

 

I'd try another set, if the mains are factory............if it's tight send the bad set back.....