Skylark_air..
So Boeing can't get the engines right on the 737?! Since when did Boeing make engines? If you mean that they had to adapt the nacelle design for the 737Classics onwards to fit the CFM56 in then fair enough, but that's because the original aircraft was designed around the lower bypass ratio and hence diameter of the JT8D engine. To maintain ground clearance they had to flatten the bottom of the nacelle for that CFM56 powered aircraft, not aerodynamically ideal, but I don't think it's hampered the success of the type.