Normal direction screwing up rendering in blender/UE4 but not keyshot? I'm playing around with a 3d tank model from a video game so I can 3d print it. The model consists of 4 parts, the hull, suspension, turret, and gun. I noticed the normals on all 4 of them are flipped in the wrong direction, but the suspension and gun still render normally in all rendering software. 

pictures on imgur

The hull and turret render as a dark silhouette in blender internal/cycles (first screenshot) and appear transparent in UE4, but render normally in keyshot. The entire model looks fine in the blender viewport (second screenshot).

In UE4 (third screenshot) you can tell the normals are wrong since the front faces appear transparent (while the back faces appear because their normal is facing the camera). Same thing happens when you enable "backface culling" in blender. What's weird and pissing me off about this, is that the gun and suspension have their normals facing in the wrong direction too, but they render normally (and backface culling behaves normally on them).

I tried flipping the normals and recalculating them ("make normals consistent" box ticked in blender), except they still render incorrectly but now the shadows are in the wrong direction too. I can't manually correct each face since the model has 30k+ faces... This is really stumping me since I've only been using blender for a couple days... Also the models have a copyright on them (they're from a game) so I can't upload it for someone to help with unfortunately.

I already used these two threads and neither worked:

Select normals pointing in a certain direction

How to make all faces flip to the right/consistent direction?
The solution is to recalculate the normals and then export it as a .dae.

When reopening it, it renders correctly.