Hi. I have an opel astra 2001 16.16V. My sub assembly was recently replaced with an imported ecotec motor and my old cylinder head reconditioned and re-used. From the start smoke came from the exhaust. then new piston rings was fitted, but after about 100km smoke appeard again. Most mechanics told me that it was the valve stem seals. Then, the cylinder head was roconditioned again with new valves, guides and valve stem seals, and just to make sure, new chrome piston rings was fitted again, but with no luck. With start-up in the morning, there is no smoke, but after about five minutes, smoke starts to appear and get worse the longer i drive. sometimes smoke will be visible on pull away or reving, but not always ans sometimes its worse than other times. someone said that the piston sleeves might be oval, but i dont thing the block had that much milageon as the origional GM bigends was still in when the piston rings was replaced and the sleeves did not even have a ridge. plse help