I would replace the chain and upper rails every 100k to 150k on an M117 V8 because the chain is so long. It will make a, "racka-ta-racka-ta" noise at startup. Also, the guides get brittle. If I am not mistaken, the M117 IS an interference engine and the valves WILL get bent on chain failure. I got mine changed for $600--cheap insurance! Hope this helps, Andrew Seidel.
85 500SEC Lorinser
83 300D Turbo