I suppose you could say that the valvetrain in any engine is a bit like my grown-up family. So long as everyone away from home stays in contact with the matriarch, all is well. However, as soon as that contact is lost - a late birthday card, for instance, or a promise to phone not honoured - then there are, shall we say, consequences. The same can certainly be said of the valvetrain, for when components in the system lose contact with each other the consequences can be more than simple...