Need help with blacked out shading on models.

[find me]

So I've learned how to import a free .3ds model into blender, export it to a .smd with source tools, then create a qc file and compile it to a .mdl and the others. It works, and I can spawn my new prop in game, but it goes completely black if you look at it at certain angles. Why is this? Here is a picture.

https://image.ibb.co/hQBmcc/shading.png

[Grodbert]

there was a similar problem not long ago, read this: $illumposition