D4 5T Hand crank tool ??

Find a rod or bolt the same diameter as the bore of the nut, slide it in as far as it will go, put a mark on it. Pull it out, drill it to a pin size as large as the cogs on that nut. If you use a long bolt, then the head is there for an impact. Be sure to round the corners off from the end of the rod/bolt where it will go inside of that nut.
WARNING! The impact will probably bend the pin you put through the rod/bolt. A better grade pin will probably cause the end of the rod/bolt to break off.
Remember this is the smallest connection to the stuck crank/piston that you are trying to put a lot of torque through. 👍

Any impact wrench large enough to break it free will likely destroy the jaw coupling before the engine turns. I may recall wrong , but I think the jaw threads into the crank, and the crank threads need to be preserved.

You are not going to get enought torque on there to make a difference, you will end up breaking the ears on that nut and you will have more problems. You can pull the injectors and put Kroil, PB blaster or what ever your fovorate penetrate is. You can also tow it in gear, but that my have it's issues also. But I would make sure that I have applied penetrate and then tried to tow and slowly engage clutch.

Sometimes there is just no easy way or short cut. In the long run, it always pays to do things right.

John

Hi, Auscuscus.
My suggestion would be to stop being so lazy and looking for a quick fix, bite the bullet, remove the oil pan and do it properly.

IF you succeed in getting the crank to turn against whatever it is in that main that is binding it up, there is a pretty good chance that you will score the bearing, the journal, or both - - - 'n' I vaguely remember somebody once saying that crankshaft bearings and journals do their best work when they are PERFECTLY smooth and round. 'Course, it may be that the above-mentioned speaker wuz 'fullabull' but do you REALLY wanta take that chance?

On the other hand, you could always take the philanthropic view that Cat and Westrac need the money from the sales of spare parts to you and that you are simply doing your civic duty by chancing ruining what might still be perfectly serviceable parts trying to do it the 'quick' way.

Just my 0.02. (Not that you should take any notice of what I think. Heck, I yain't even a Meccano muck-kanic.)

use a chain wrench one with a bout a 30 in handle the chain is the right size to fit in the pulley groves that's the way i did my d 4 trun one way turn the other i use marvel mystery oil have for years that's what my grandad did back in the day worked for him and has for me as well these last 50 yrs the d 4 runs like a champ

I've never had any luck freeing up a stuck main engine without pulling the head first. Then the fun really starts 😆

Thanks for all the good pragmatic advice. Just had a bad run with the pony for 12 months so was hoping the main was only ' just' stuck. Not years of sitting. In saying that she had plenty of water in the pan. Deas you would know the Parryville hall west of Denmark. She is between there and the coast and we get 800mm of rain a year. Somehow a big share of that got under the tarp puddled on the side of the head and leached under the rocker cover.

Can I leave the injectors in place if I pull the head. Then pull them in the workshop ? Save me making a tool to take to the bush.

Hi, Auscuscus.
Yes, I do remember the Parryville Hall - went to many a dance there in my (MUCH) younger days. People named Bell had the farm over the road from the hall and another family named Cuffley were further down the road that ran off opposite the hall. We had a farm that backed onto the old William Bay Hall, back towards Denmark.

Hadda lotta fun around there. I can also remember the rainfall in that area. I remember chasing cows, sheep and 'roos in that rain, not to mention going fishing in it. A common saying about the weather around there used to be that it rained right up to the end of the year and started again on January 1st. Summer was a good one the last year that I lived there, 1959. It came on a Wednesday - lasted all day too.

I can also remember seeing the Southern Lights from the hill behind the house on that farm on several occasions.

Yes, you can lift the entire head as a unit and take it back to the workshop for further investigation. Try to remember to disconnect the injector pipes and water lines before removal. LOL.

Cat used to make a special tool for pulling the pre-combustion chambers that looked like a short, hex-head, threadless bolt, about 7/8" - 22mm - in diameter with a rather fine straight spline where the threads woulda bin.

When I read 'main' in your earlier post, I immediately thought Main crankshaft bearing. Dunno why. Still, I have never been a fan of using brute force at any level to free up a stuck engine. The potential for causing further damage is too great.

Just my 0.02.