John, after some thinking, I don't think its the timing chain. But if it is the original timing chain, it should be replaced, unless you want to replace the motor one day. A timing chain with 270K is a ticking time bomb, stretched or not. A stretched timing chain will result in hard starts, for the valves on the 603 are hydraulic. Your injection pump sounds like it need adjustment or overhaul. Fuel delivery in these things is crutial...