bodyart,

The prudent thing: check the cam timing before replacing the chain , yes you got it.

Always test, measure and diagnose before you replace parts.

IMHO, 15,000 miles too soon for next valve adjustment on older engines. I checked the valve clearances on my '79 300 SD at 25,000 miles since the last adjustment and not one valve needed adjustment. I think that's because the valves and seats work harden and need less adjustments on higher milage engines.

Measuring the valve clearance before you loosen any of the adjustment nuts may save you a lot of work and time. I'm guessing a only a few or none of the valves will need adjustment unless its been many miles over 25,000 since the last adjustment.

P E H