and it is important that, following maintenance, adjustments are made correctly. Clearance is allowed between the valve stem and the rocker arm when the engine is cold. As the engine attains normal running temperature this clearance is taken up by expansion. If adjustments leave too little clearance then it is likely that the valve will be prevented from closing correctly by the valve gear, resulting in gas leakage, burning and deteriorating performance. Conversely, too great a clearance may result in reduced valve lift and duration of opening, mechanical noise and reduced performance levels.