I’m modelling some sort of turret thingy, and kinda making it up as I go along but I’ve come across this problem and its really annoying me.These weird lines have been appearing on the surface of a certain part, they look like cracks or fractures but I’ve not fractured the object at all, can someone give me a hand?
they seem to only be there after using subsurf Modifier?
What does the geometry show, are there duplicate faces? Are those lines edges in the actual geometry?
Do you have a texture on the model, does the cracks come from there?
What modifiers you have on the model?
Its not similar to the geometry of the mesh, i made sure there were no doubles and I haven’t applied any textures to it yet. There is only a single subsurf modifier set to view: 2 render: 3
You have a bunch of duplicate vertices on what would be MainBody for this. That could be a reason why you see these lines.
Unfortunately i’m on some stone age rig right now and rendering even 20 samples would take whole next millennium. Try to W remove doubles and rerender.
It would have helped if you had pointed to the exact place where the lines appear.
Looks like your meshes are fine but the topology is not good for subdivision surface modifier. If you add it though, put the modifier on top the edge split modifier. Modifiers are applied from top and edge split does what the name says, splits the edges so subdivided result of that would make a lot of holes in your mesh.
I’ve tried everything now, i have no idea why it does this. There are no duplicate faces or vertices (I’ve checked) and it seems to happen even if i don’t use the edge split on this specific part 
I think I found the problem.
When doing a preview render close up, having a high clipping end value in viewport clipping induces these artifacts. I think the term is Z-fighting. Putting a lower value (like 100) solves that.
In the future, could you please upload images that have more information in them than that. That little “z” in the lower left corner in your screenshot gave me an idea to try this again. Adding the .blend file itself without someone asking would speed things up too.
Problem solved 
thanks to JA12 and everyone for all of your help. Sorry about the lack of information, I don’t really post about problems regularly so I didn’t know what to post.
That’s ok. At least you posted a screenshot (something to work with) in the starting post, unlike many other people.
Personal information and such are not needed and should be left out, but everything else can give valuable clues of what is going on.
With all respect and blender on win and linux with default distance settings:
