element_exclusion_list write

1st: it would be better to remesh your geometry, remove all unnecessary holes, phases, screws and so on, than save your CAD file as step file and load it e.g. in Netgen (a great opensource meshing tool). Than use meshing options and set maxsize=100 and min size=99 (values depends on size and unit system of your geometry !!. try different values but make sure min=max-1 !) this will give you nice equilateral triangles.
When you can't optimize your mesh here is the "trick" for element exclusion list:
#1st run on single processor with:

fix cad1 all mesh/surface file CAD/fixed1.stl type 1 element_exclusion_list write blacklist_top.txt
fix wall all wall/gran model hertz tangential history cohesion off rolling_friction epsd2 mesh n_meshes 1 meshes cad1
run 1
Q #break simulation here

this will generate a blacklist_top.txt file with the numbers of bad triangles
#2nd run (is allowed to be a multiprocessor run)

fix cad1 all mesh/surface file CAD/fixed1.stl type 1 element_exclusion_list read blacklist_top.txt


The exclusion list will remove triangle from your mesh, I guess this could lead to holes in your geometry ! Be carefull and have a deep look at the dump stl result file !

Best,
Christian.