im putting my engine back together just had the head oringed titanimum retainers and keepers and everything else. my question is the oring that goes on top of the injector nut mine are dryrotted and cracked and my cummins head gasket set didnt come with new ones. would i be ok to put it back together without them. im dying to hear this thing purr, but dont want to screw anything up

 

Oring on TOP of the injector nut?

If you are talking about the oring that goes on BEFORE tightening the nut/fuel line to the injector, then that is just a dust/debris shield. You wont hurt anything it just helps to prevent crud from getting in there.

Heres a pic of an injector install kit. If its the black oring then you can install it without it.

http://www.usdieselparts.com/moreinf...duct_ID/57269/

 

Like Dman said its just to keep junk from getting down between the bore and the injector body.