I have a 96 Nissan Sentra GXE 1.6 and the car has a few problem. First, whenever i start the car up. White smoke and oil would come out the muffler. Also after when taking the spark plug out. I could see oil in the pistons. The car would not overheat during idle and after driving it. And it would shake during idle and shake even more at acceleration. Do you guys think its due to a bent valve. Or could it be even worst?

 

Most likely piston rings. compression/leakdown test