单项选择题
A.Worn intake valve guides
B.Pitted pre-combustion chambers
C.Loose valve tappets
D.High exhaust back pressure
单项选择题 Late fuel oil injection in a diesel engine can result in （）
单项选择题 A crankshaft whose center of gravity coincides with its center line is said to be（） Ⅰ.statically balanced Ⅱ.dynamically balanced
单项选择题 In a trunk type diesel engine piston, the thickness of the head or crown is determined by the（） Ⅰ.statically balanced Ⅱ.heat dissipation requirement