Today we tried pulling the precups using the correct 5F8353 tool. The goal was to switch them out for new aftermarket ones with glow plugs so the engine will start easier. The 8U was converted to 24v electric start years ago, but on cold mornings it doesn’t like to start without the help of ether, which i absolutely hate using. 

We started off with the splined cat tool and a 1/2” impact.  Zero movement. Then we moved on to a 5 foot breaker bar. Zero movement. Then we upgraded to a 3/4” impact. Zero movement. I threw the towel in before trying the 1” impact. I’m afraid of pulling the threads right out of the head.

I feel defeated. The block is drained of all the coolant.  I bought $250 in premix John Deere coolant (I use it in everything and swear by the stuff….Ph correct and won’t eat through liners like cheap stuff) I’d hate to have wasted all that money in coolant for nothing. Does anyone have any other tricks to bust them loose or am I at a dead end?

Thanks
-Nick

I don't like using ether either they get addicted to it real quick. squatch253 and his dad has some videos on youtube that shows them cranking on some D2 precups.I highly advise you to watch them. squatch253 and Senior did not want to use high heat to keep from wrapping the head. But thermal shocking the area should help, dry ice and a sm propane torch to WARM up the area (no warmer than 350*F-400*F) Cycling till it your sick of it then try one more time the next day.
I also have to mention "Marty T" a youtuber heated the puppy-water out of a D2 head to remove some precups.
That is my best advice,.I imagine there are better ways of doing it but it is really cold here so letting it set outside works for the cooling part.
Good luck

You don't mention s/n's. I hope you are aware that glow plug pre-cups will not fit early s/n head without machine work.

Serial 2517. Definitely was not aware that machine work is needed to fit glow plug pre-cups. Is there a writeup available anywhere of what needs to be done?

No write up that I'm aware of. The chamber bore diameter changes from 2-1/8" diameter to 2-3/8" diameter to acommodate the glow plug version. Or go to a later head 8U5786-up or 9U11705-up. Head casting number would be a 7F7878

just install a thermostart plug into the intake manifold between the air cleaner and the intake. put it near the mouth of the intake though. you caan use the pony gas tank as a diesel reservoir for it or plumb it into the fuel tower. get one that is 2 volt. i have them on cummins,perkins, new holland diesels and they all start second crank. coldest i have used is 25 below zero F.

bestfarmparts.com/White-Oliver/Glow-Plug...lt-White-Oliver-1250

I haven't used one but here's how it works....
 

a thermostart really isn't a heater so much because it only produces flame for just a few seconds but it sure kicks off ignition of a cold diesel engine and saves battery. my new holland chore tractor starts and runs every day no matter the temperature and it doesn't have a block heater,just a thermostart. coldest i have used the thermostart was neg 25 three cranks and we were off to work.