Let me provide some general numbers.
USA
Built 6,500 out of 97,000 artillery pieces so 6.7%
Produced a like amount of artillery shells; 50 million out of a total 789 million 6.3%
Built 266,000 out of 816,000 machineguns 32.5%
Built 4.8 million out of 31.6 million rifles 15.1%
Built 14,000 out of 140,000 aircraft 10%
Built 33,000 out of 162,000 aircraft engines 20.3%
Those ignore large shipments of High Quality steel in 1917/18, the US, France and UK concluded a deal to ship raw materials and provide funds for the UK and France to produce weapons for the AEF. Otherwise the US was going to have to take over orders intended for he UK/France and or build up even more physical plant which would have taken 12 to 18 months to spin up.
Lets ignore the AEF manpower on the line and in the pipe
The US Treasury Department was supporting the Franc and Pound to the tune of about 35% and 10%. Also by the end of the war all neutrals were reluctant to take any more gold than they already had. The UK wasn’t bankrupt in 1919 but they had taken out huge amounts of loans from the US government and US private firms. Britain and France had sold off a great deal of their foreign investments by 1918 getting 60 cents on the dollar of pre-war value. The critical date for loans is in 1917 if we assume no private loans the Entente have to sell off all their investments; by 1917 the $7.5 worth of UK foreign holdings will be gone. So it would be possible to hand wave away the effects of a neutral USA till mid 1917 or so by a cash and carry response. I suspect France / UK would over time start to face problems sooner between lack of treasury support for their currencies, increased transfers of bullion over historic and general crunch forcing less and less on sale of investments. So the money could run out late 1916 or so; lots of hand waving on my part as I have no way done a detailed study of it.
What happens once France / UK run out of cash? The war doesn’t end, like Germany and AH they resort to other methods to continue the war; increased war taxes, internal war loans, credit manipulation, greater direct control over the economy, rationing, etc. Net effect is the Entente fights on but at increased social / economic cost (more inflation and war weariness) and lots more pain once the war is over.
1918 is a different matter the vast majority of US production comes in 1918 and total production values for entente have reached a plateau point. Italy is static compared to 1917, Russia has none really, France only 12% gain with the UK picking up the slack. With no US loans and foreign investments sold off the entente is going to run into a brick wall on production values, they might even start to drop a little as between currency deprecation / inflation and the rest raw material imports become harder; most likely just static or only small increases. The internal economies keep working but imports slow down dramatically.
If we assume worst case the Entente to be blunt are totally and completely screwed; especially if the USA has gone to some type of armed neutrality response. If the Germans can import even just food most of their problems go away. Worse yet a more strident USA will get the other neutrals like the Netherlands, Denmark, Sweden to refuse to clamp down as hard as they did on transshipment of goods to Germany. So we have to assume the USA doesn’t go that far, the blockade isn’t broken but it doesn’t lift a finger to help entente and pure cash n carry on arms, material, etc.
Even then I can’t in all honesty think of situation as you suggest. With no USA coming into the picture it totally changes the Central Powers strategic outlook for 1918 campaign year. They have no reason to attack that year beyond either limited attacks or a weighted blow vs. Italy. They are not in a race with US reinforcements so they can stand in place. The food situation had actually started to improve that year; still it sucked totally and completely literal starvation level rations.
The Germans would have to do the dumb move and attack as historic smashing their reserves and will to fight with the all out attack in the west. I have my own thought on how that campaign plays out if the entente troops don’t know that endless rows of fresh troops are on the way or the logistic push the USA gives is reduced or missing all together. Once the attack is spent the Germans begin to pull back to shorten the front again. AH is also stupid, much easier to believe their command and control was rather shot at this point and they smash themselves. That winter and spring the Britsh / French launch attacks with large numbers of tanks as the core of their offensive firepower. AH then comes apart when the Italians attack.
The Germans then have to rush massive amounts of troops to shore up AH on the Italian Front and in the Balkans. Bulgaria pulls out as historic. Maybe Romania gets itchy and tries to reenter the war. This increases the degree of German over reach having to fight on a wide arch from the North Sea down to Switzerland, Austrian Alps, Balkans and to the Black Sea; plus garrisons to hold down the east. Chuck in your Polish uprising for good measure.
Germany chucks in the towel and asks for an armistice. I strongly doubt it’s the historic armistice terms. The Germans retreat to pre-war border and go to Paris for peace talks; but their armies keep their weapons. Maybe they even agree to the same in the east, Lenin at some point renounces Brest-Litovsk just as Romania did the treaty of Bucharest. Even if he Germans do AGREE to a pull back the Freikorps are going to be active in the east and at an even higher level than historic I suspect. If the allies go for hard ball its going to be very ugly as the Germans threaten to restart the war. The German Government plans Kaiser Willy for the mess and refuse to pay the tab so to speak.
In the mean time the Germans crack down on the Spartacist and all verity of leftist revolutionaries even if the SPD is in charge of a German republic. Help for German nationalist in blood letting within the now very former Austria Hungary occurs. Figure all side are running guns there and to a lesser extent in the east. Both sides can play that game in AH but the Germans are much better off in Eastern Europe.
As to final terms?
No reparations except for some to Belgium.
Territory changes…
German colonies gone as Historic
Alsace Lorraine to France
A rump Poland in the east sans Silesia, Posen, and Danzig but it gets ex Austrian Galicia. The Poles then go for empire into the chaos of Russia. Maybe even the Germans are helping them and perhaps even the French as both sides play for influence in Warsaw.
Perhaps Schleswig goes to Denmark but its not a given and I doubt Belgium gets its little bit.
No Saar, DMZ Rhineland, military restrictions etc.
The German fleet... Its not gone but the Germans would be most likely to deal on that point if restrictions occur, after all the fleet didn't achieve much. Figure some type of crazy half backed agreement on fleet strength between France, UK, Italy and Germany sorta a proto Washington Treaty which never occurs. Even then its more likely an agreement on construction numbers rather than active totals.
If it hasn’t already Austria-Hungary is just gone. When the German areas of Bohemia / Moravia (Czech) attempt to join Austria it succeeds. The Germans send guns and more Freikorps show up, whatever military Austria has held on to gets involved. This plays out as part of a mad scramble across the former Hapsburg and Romanov lands. See similar things in the Baltic’s, Hungary, Ukraine, etc. Romania jumps into seize Transylvania, Serbs go for their empire, perhaps Italy plunges into the chaos, etc, etc. With all sorts of ethnic violence. Very possible to see large scale battles taking place, in local terms over this area as these wars of succession plays. I won’t even pretend to guess how that witches brew plays out in the long term other than to say that it would be ugly.
At anyrate sooner rather than later Großdeutschland occurs as the German areas of Austria join with Germany. The allies of course will throw a fit but as with the rest of this I am assuming that once the guns silent there won’t be the will to start up the war again. The French might be pissed off enough but I doubt London would and without that backing France has no choice but to accept the peace. Especially as increased costs of the war have come home to roost and I wouldn't be suprised to see some fairly impressive displays of disorder occur in France and Britian.
The early 1920's become know as the bloody 20's as was wars of succession and civil disorder are the norm for most of Europe.
PS is this more helpful?
Michael