I torn my engine down to find theres a crack in between cylinders 7 and 8 the engine was running good before I torn it down but white smoke was coming out of exhaust. machine shop told me if water was not get into cylinders and if no water was getting into oil it was fine to rebuilt. I rebuilt the engine and white smoke is still come out exhaust but it runs good,compression good, no water in oil. why is my engine smoking I know its build right?

 

If there's a crack you should fix it. If the actual cylinder walls are cracked you need to have the one or two cylinders resleeved at the machine shop that are cracked. Magnafluxing the block will show these problems usually fairly well. If your local machine shop can't resleeve cylinders - find a new one. You might cheap out and get away with tearing the block back down - cleaning it up and using JB Weld in the crack (as long as it's on the top deck and not fractured into the cylinder walls). You could use a dremel tool with a metal cutting disc to open the fracture at the edge (not at the sleeves) and make it easier to shove the JB Weld in. Make sure you give the putty a full day and warm environment to dry right though. Then grind (dremel sanding drum) and fine sand. It might work in the cylinders too - but I wouldn't recommend it due to the volatile environment and different wear properties between the steel and JB Weld.