Hi We have a Vauxhall corsa 1.2 16v 2005 48,000 miles. Had a misfire and traced it to a valve rocker that had come off the hydraulic tappit and partially jammed one inlet valve open. Found that the cam shaft bearing caps were loose repositioned valve rocker and tightened bearing caps to specific torque. Ok for a few miles then the same thing happened. Bearing caps still tight but now a different rocker has come away from the hydraulic push rod and jammed another inlet valve open. Put this right again vehicle ran again for a few miles and again the same thing happened on a different inlet valve. I did notice that this only happened on starting from cold or when the engine had been stood for six or seven hours. I now in a morning put the vehicle in gear and gently rock the car to rotate the engine a couple of turns this seems to overcome the problem I have changed all the inlet rockers the engine oil level is ok and the type of oil is 10w 40. It seems to me that there may be a lack of oil between the cam shaft and the roller on the rocker however there does eem to be sufficient oil around the cam shaft valve area. Any suggestions would be welcomed on how to solve the problem. Graham
27th May Additional information -
I did check with the vauxhall main dealer if the cam shaft bearing bolts were stretch bolts - they didn't appear to know. I have however renewed all the cam shaft bearing bolts and they are still at the specified torque. Yesterday to start the vehicle i again rocked the engine in gear and again it started fine and I travelled approx 40 miles without any problem. However, this morning I deliberately did not rock the engine and immediately I have a misfire and I have found that number three cylinder number two inlet valve (6) rocker has come off the hydraulic tappit and jammed under the cam shaft holding the valve slightly open. Again a quick flick with the screwdriver and the rocker is back in place. Fortunately it is not opening the inlet valve far enough for it to hit the piston. The cam shaft bearing surface is perfect and does appear to be well lubricated. Looking at the exhaust cam shaft none of these rockers have moved but where as the direction of rotation of the inlet cam shaft tends to push the rockers/roller towards the inlet valve the exhaust cam shaft is pushing the rocker/roller away from the inlet valves and towards the hydraulic tappit (pivot). So the exhaust roller has got nowhere to go. As stated all the rockers are new and the rollers rotate very freely. All the timing gear is in good condition no noise when running and I can not see any wear in the timing chain or sprockets but I don't think this would be an issue.
I did consider weak inlet valve springs but I think it would be too much of a coincidence to have a number of inlet valve springs suddenly lose their tension all at the same time. If it was continually happening on the same valve I would consider this a possibility.
An early response would be appreciated.