I have a 2005 2.2 Zafira, which has just turned 50k miles and had the camchain and tensioner replaced a few years ago (cheers Benny). It was running fine, but due an annual oil change, so I replaced the oil with 4.75 litres of Halfords semi-synthetic 10w 40, plus a new filter. I took a brief test run and it seemed okay. The wife has since driven it a further 25 miles, and now it is sounding really rough, with the tappets hammering away like my old Escort on a cold morning, (except things don,t improve) and general thrashiness - it's not nice. I'm at a loss to know what could have gone wrong. I carried out the same routine a year ago with no problems, but now I'm concerned some expensive damage could have been done. Anyone had a similar problem, or have any idea what the problem might be ?