OldIHC

Here is a pic of the internals, less the charging board which would sit in the center recess.

One Issue I had, on the heavy Delco starters, the nose cone bolts on with 6, 1/4" allen head bolts. These loosened over time, something I have never seen happen before on a Delco starter. Often the 5/8" bolt holding it to the bellhousing will loosen, but this is the 1st time I have seen these be a problem.
I am guessing here, but I think the amount of current, available all at once, is too much for the motor. Series wound motors produce maximum torque with a locked rotor, as the motor speed increases, the torque goes down. Batteries have a relatively high internal resistance, this is why, while one group 31 battery can contain enough power to crank a big bore diesel, it takes 3-4 to get enough current at one time to do so. The Capacitor has very low resistance, so the limiting factor on how much current is available to the starter is the resistance of the cables and the windings in the starter. With all that current available when the contacts close in the solenoid, the initial torque is much higher than when 4 group 31's are used. It is part of the reason why the Maxwell seams to have little trouble cranking. There isn't the normal slow start to the crank, it spins almost instantly at full cranking speed, it gets to that speed even faster than air start.
Capacitors are weird things, they have almost no resistance, and if shorted can release vast amounts of current almost instantaneously , you most defiantly don't want to be holding a wrench in your hand if it touches both terminals!
If the bolts keep loosening or if they break, I will try going to a slightly lighter battery cables to introduce some "artificial" resistance in the circuit, if that doesn't work I may go to one of the newer PMGR starters. While these are still series wound, the field is a permanent magnet and the torque is less, they overcome this by spinning the armature faster and using gear reduction on the drive. My hope is that the torque will be less on initial cranking. My last resort will be to go to 24 volt unit and much lighter cabling.
Who thought "too much torque" would be a bad thing?

I keep a GB40 lithium booster in my glove box as I have a collection of weak batteries in other equipment. I have started and run my '41 IHC with only the GB40. Next size booster up is GB70.

The Maxwell isn't a booster, it is the only thing connected to the starter. Provides 100% of the cranking 100% of the time.

I haven't updated this in a while. I had a unit failure about a year or more ago that was replaced under warnentte for no charge. A few months ago the original Delco MT42 had a solenoid "weld" and I was under load, so had the starter replaced with a modern gear reduction unit. I can't say the newer starter faired any better, it had a "relay" mounted on top of the solenoid, like a Ford type but smaller, the truck also uses a "Ford" style at the battery box, since I didn't do the install, the guy just took the old solenoid wire and connected to the motors "relay". Didn't take a long time for that relay to start acting up, You'd have to hit the button repeated times before it would kick. I just took it out of the circuit.
I kept the old Delco and put a new contact kit in the solenoid, so it will be ready to go on next failure.
It seams these capacitors are hard on contacts! too much current all at once.
The 2nd unit has had less terminal/connection problems than the original unit, not sure why.

Today I went down to the bodyshop where this truck has been sitting since July! It hasn't been started in several months. Today it is 3 deg F. I turned on the Espar for 15 miniutes while I did some other work, and it cranked the engine over great. The truck that had been sitting for months fired up like I had run it that morning. All in 3 deg temps! I guess that says a lot on how long you can leave it. I let the truck run for over 2 hrs to bring the deep cycles up, they never fully recharged in that time, the current only dropped to about 10 amps, but didn't want to babysit the truck longer.
Now that I got the engine to light off, I need to light a fire under the body shop to get the work done!

Truck has been sitting around for months, and still fires right off when started. While I started out thinking that this was 2nd best to air start, I am becoming more at ease with it. It's ability to "recharge" itself after a failed start attempt, has a definite advantage over air start which would require a air compressor or drawing down of several tires to try again.
The draw back is it still uses high amp connections which is the bane of all electric starters. The ability to go with 24 volt cranking with a 12 volt system would go a long way to mitigate the high amp problem.
If the air start ever has a major problem, I think I would opt for the 24 volt unit to replace the air start with. With 24 volt cranking the current draw will always be below 1000 amps, often well below that point, which should go a long way to mitigating connection problems.