Thats because the original engine was trouble prone. Deere basically gave you a 50 series engine if you would pay the installation labor. There was something like a 2500 hour cap on the program but many dealers didn't look at the tach very closely.I have seen numerous 84-8630s over the years with the 50 series engines.
you cant put the 6619 in a 8430 because they have the 466 and the way everything sits under the hood is different the 8630 and 8640 and 8650 all have the 6619Hopefully the guys on here that know, will get you the information. Seems like a good idea. I have seen numerous 84-8630s over the years with the 50 series engines.
You must have a lot of hours on your 4430, as I have had more than one tell me that they had over 10,000 hours on theirs and still going strong.