I must be losing it:(
Gordon is right,
In series a total of 1200 amps or there abouts should be more than enough to crank the 40MT starter. That's assuming the batteries are in good condition. The 2000amp total would be way overkill.

Two 154ah batteries wouldn't even make the performance graph;)
Must be one tired engine.

My D4 7U takes 2 of the 3EE batteries. They are the long skinny 12 volts. They fit the battery case like it was made for them. Of course this is a different location than the D4D you are working with. Mine is a factory electric start and they are located where the pony motor would have been. The battery disconnect is dash mounted on the mine and takes a cat key. By the way that is a nice looking tractor that you aquired. Good luck

Sounds like a dragging starter or bad cables/connections, if the batteries load test alright. Glow plugs would need to be checked for operation as well. I would think that a low compression motor would spin easier. Unless there is some other excess drag somewhere.

OM ,the engine has new liners ,rings etc due to water damage as did the head ,i reground the valves /seats to the best i could ,but could really do with new seats and valves ,also the injectors could do with checking
but at the time i did not have the funds ,now i am lacking the time

is this of any help richard
cheers graham

Thanks for the guidance, fellas. Looks like I need a bit more patience.

How do I test if it's charging alright? reason I ask was when I took it for a run the ammeter seemed to stay on '0'. I was expecting it to move off the mark slightly.

Doesn't seem like it is charging.
Check the battery voltage when it is not running, should be 12v or a little more.
Check again when running at something higher than idle rpm. Should read between 13.5 and 14.5v. You know the rest:)

Yes, d4c24a....I know that song:)

If it is a 24 volt starting system, wouldn't the charging system also be 24 volt?

Right again:) only hitting on 1/2 cylinders today.

Same drill...24V+ at rest.....about 27V+ at running speed.

Richard you can test charging with a 12 volt tester when the engine is running, just put the test leads on to one battery at a time, you should have a reading of 13 - 15 volts. 13 is minimum and 15 is absolute maximum. 13.5 on each battery is therefore 27 V as OM said. Our A25s charge at 29 volts when batts are low. Check all your connections especially the eath points. I would fit an isolator switch myself.

Graham i have to confess i just sent a D6M head to finning for refurb.
Pressure test, valve guide replacement valve fitting and lapping, light skim and injector sleeve replacement, picked up and to be returned £288.00. Rekon your 330 head weighs more than our 3116 so maybe they wont be able to lift it eh Lol
Gordon.