I have a block with only the crank, rods and pistons installed. Is it safe to wash it like this or its not good getting these parts wet? Also what should I wash it with? Thanks

 

It doesn't sound like a good idea.

 

if its already that torn down I would just tear it apart, mark everything carefully and then wash, reassemble, unlesss its in the car, then I would assemble the motor, run it, then clean the outside that way.

 

The problem with washing it with all of that still in it is that water and solvent and the like will get into passages and galleys and never come out. The rule of thumb is to strip the entire block bare (including removing the galley plugs for the oil passages) and washing it bare. That way you can rest assured that you have gotten any possible contaminents out of the block and it is squeeky clean, and dry, and ready for assembly. It just isn't worth cutting corners.