The cracks are due to expansion from heat. The center of the piston is hotter than the skirts. You will probably notice that the cracks occur at a 90° position to the wrist-pins.
I'm confused by the piston enumeration, it is usually #6 & #5 that bake.
Replace them and the other piston rings and you should be good to go.
Just out of curiosity; Does the truck warm up before a hard run?
6naline01 - I was musing at your profile statement (comifornia) Is that in refernece to the government of your state???
Well The cracks are on the manifold side and ya it is in cyl #1,3,5. I would always worm the before a hard pull or run. After the retirement of the truck I had planed to make it in to a play truck but after seeing that I'm having second thoughts about it. it has been turn up all its life
What would happen if you left it be? How do you oil samples come out? These cracks look to have been there, or did they split from hydrolocking?
I don't know how long they have been cracked for but I’m most likely am going to drive it like that for a while. My bank account has disappeared. I will most likely do the work in the summer and then I can do it all at once.
Keith