Hi I'm working on a jd4020, I rebuilt this tractor a couple years ago. I put a new reliance piston and liner kit in it,had the pump checked out and had the head gone thru by a very good machine shop. I had all the pencil injectors tested and 1 was bad so I replaced it,prior to the rebuild the tractor smoked and used oil quite heavily,afterwards the tractor still smoked more than I was comfortable with,but didn't use oil. It has now maybe 70 hrs on it, and last summer the head gasket started to leak some on the right side while the owner was out round baleing. This is believe to be my fault because I DID NOT replace the head bolts and I DID NOT use any hy-tack and i DID NOT retorqe the head bolts.So I pulled the head off to replace the head gasket and found one piston severely carboned up ''almost the consistency of mud''. The tractor has no odd noise's and runs very well,starts right up. So with all that said my gut is telling me that I have a injector issue, any thoughts would be greatly appreciated. Thank you