http://www.peachparts.com/shopforum/diesel-discussion/411714-om617-torque-values-rocker-arm.html

Also make sure the rocker arms not stressed by the cam lobes on R&R :
https://www.youtube.com/watch?v=O2T82oEFQ2I

And make sure the centering sleeves for the towers are all present and in good condition.
http://www.peachparts.com/shopforum/diesel-discussion/292821-om617-rocker-arm-problem.html

Good luck !