M52 cam sprocket tightening torque

[slvrXI]

On the intake cam... the shim that holds the spring washer. On the image it is the nut labled as 12. There are 3. I was told 15 Nm and I ended up stripping the nut off of the stud, and now I have new studs and nuts and I'm gonna try this again...

http://www.realoem.com/bmw/diagrams/d/a/9.png

Thanks for any help...