Prior to the service if you started the engine from cold you would get a knocking noise,, but this only lasted 5-10 seconds at most. The knocking is there all the time, regardless of engine temp. When you rev the engine the noise is greatly reduced (or might not even be there at all), and it is most obvious on tick over. As I explained I have run the engine to working temp, added STP engine flush and let the car tick over at about 1800rpm for 20 minutes, then while the oil was still hot enough to burn your fingers, I drained the sump, and refilled with 10W40 semi s.........made no difference whatsoever, which brings me to my previous question: is it possible that one of the lifters may have been damaged as a result of using a multigrade oil instead of SS which the car has been running on for years. one more point, but I doubt it is connected, my car likes oil, and if you give it a squirt on the open road, there is a nice cloud of blue smoke from the tail pipe. I had intended taking the engine out and having it re-built (any suggestions as to engineers in the UK or Ireland who do this work), looks like I might have to do this sooner than I had planned. BTW the engine is a 8V 1800 EV type engine