Odd starter problem, pleade help quick!

Hi!

I have an odd problem with my starter, it's a 1.9HP SUMMIT mini starter sitting on a TF A904 and a stroked 318 with no odd firmness when turning it by hand and the teeth on the turbine seems fine, none missing or anything.

It's wired with 0 gauge cable directly from a brand new 120A Varta battery, engine and chassi ground is also 0 gauge and properly fastened. I have also had a Mercedes Diesel with jumper cables between batteries to get additional power.

The solenoid cable is about 6mm in diameter and goes through the starting relay which is also fed with a 6mm cable.

Now, the thing that happens is that when I turn the key the starter pulls the engine between 0 inches and a full turn, normally about 2-3inches before the startgear seem to pull out and you get that horrible "SSKKKKKRRR" noice starters can make..

I'm kinda stuck, can't figure out what the problem might be..

Oh, and btw. The starter is brand new.