ah year got it working, stupid me:

1/16 is an integer division XD
it must be:

1.0/16.0

However, i noticed a problem with the texture filters. Imagine we have a dirttile on our sourcetexture and its surrounded by pure white. Now i place the uv quad on this tile.

In the engine, white very small stripes will occur between the tiles. Disabling filters helps, but sometimes a little white pixel pops up, not so noticeable but anoying.

I solved it, by correcting the uv quad position. Iam shrinking the quad by 0.001, which resolves the white line issue(even with enabled filters) but does not end in visible tiling. This seems to be a valid solution, anyone another idea or something why i shouldnt do this?