Messed up blender models

I've noticed a really big problem with importing models from blender into unity. I make a model that I'm happy with, and when I import it into unity part of the model is missing. I've experimented with it a little by making the model piece by piece, importing it, and seeing if the model would show up. Eventually, parts of the model don't show up. I know unity has a polygon limit of I believe 65000, but my models are very low-poly. Does anyone know how to fix this. Any help is appreciated.

 

This is almost always because the normal for some of the faces of your model are pointed in the wrong direction. Usually inwards instead of outwards.

In Blender select the missing parts of your models and type <Control-N> to reverse the direction of the incorrect normals, then you need to redo your UV maps and textures it you aren't strictly doing materials.

 

Sorry it took me so long to reply, but thanks, I'll try that

 

It fixed one face, but the other two faces were only partially fixed. Anymore suggestions?

 

Did you "select," the entire model, in edit mode and then press Ctrl+N?

 

No, it didnt work.

 

Any solution ?