单项选择题
A.clogged lube oil piping
B.excessive valve-guide clearance
C.high lube oil viscosity
D.low lube oil temperature
单项选择题 If the diesel engine fuel injection timing is changed to delay the start of injection until the pistons are at top dead center, the engine will（）
单项选择题 A condition that can increase the foaming tendency of lube oil is （）
单项选择题 In a diesel engine, when refitting piston rings you should （） Ⅰ.check the ring gap at the smallest diameter of the cylinder Ⅱ. Remove carbon from the ring groove