what all must be done to change out the valve springs to the heavy duty ones? does the head have to come off?

 

Nope pull your valve covers and have at it some guys do 2 cylenders at a time which is ok I did mine one cylender at a time just to be on the safe side but I changed all 12 not just the ex springs. Put a new belt on if you haven't recently as if the belt is old and worn you won't be able to turn the engine over by the alternator

 

Its pretty easy to do. I did mine after reading this write up:

https://www.dieselbombers.com/cummin...eplacment.html

 

That is a nice write up. When I change valve springs, I remove the injector and use a tool that goes in the injector bore and apply air pressure to it. Then I replace the valve springs. I also place my leak down gauge on my air supply line and after I am done replacing the valve spring, I check the cylinder leak down to get an idea how good things are in the engine. It'll tell you if you need valve work or if your rings are weak.