Might have coolant in one of the cylinders and is hydro-locking ?....bad head gasket can cause that..
Pull the spark plugs out and try turning it over again by hand,if it makes a full revolution without any binding ,and some coolant comes out of one of the plug holes,you found the cause..

If the tractor has a exhaust stack with no flapper on it ,maybe some water made it into a cylinder and froze ?..

It is possible for an engine that ran ,to develop a stuck valve or lifter after it sat again,but it'd take more than a few days to rust up enough to do that..

Do NOT try using the starter until you can get the engine to rotate 2 complete revolutions by hand first. It can result in expensive damage to the engine.

And to follow up, if when pulling the spark plugs you get some fluid coming out the spark plug holes, I would suggest checking the engine oil for contamination (by whatever's in the cylinder, either fuel or coolant and changing it if it is contaminated. And also spin the engine over, with the spark plugs out, a bit more using the starter, as it spins the engine faster and will force more of the fluid out the spark plug holes.

Thank you all. I have done all of these steps suggested. As I turned the engine all valves at various times opened and closed so it appears the lifters are not stuck nor a valve staying open. There was no fluid in the cylinders. The only thing I know to do before attempting to find a mechanic, if there is one who will work on this tractor, is to pull the oil pan and look from below. Any other thoughts?

Is there any sound when it stops? Is it an abrupt stop? Can someone rotate it back and forth by hand without the plugs in it, while you listen for any sound and try to determine its location? Observe the valve locations when it stops. Always the same position? Which cylinder is TDC when it stops? Sometimes you can narrow it down by the sound it makes. "Clunk", "clank" or "tink" might indicate whether a heavy part such as crank or rod, or a valve or other smaller part.
I wouldn't push it hard in any tests you do. If it can't be found out by observation and listening, then a tear down is in order. You might start with the pan and see where that leads you. Depends on how much you think you can do in your own shop.
Good luck, and let us know if you are able to diagnose this issue. That might help others.

And is it a hard-stop within 1 full revolution, or is it within 2? If it's within 1, that is more likely to be something attached to the crankshaft, within 2, it also involves the camshaft/valves.

If it has an internal alternator then you could have some thing stuck between a pair of magnets, a loose magnet or some thing lodged in between a pair of coils.
Pull the flywheel off and see if the engine now rotates
Pull the belts/ blades off the PTO end and do the same
If the engine still stops then you have something that has come loose inside the engine.
In most cases it is an easy fix if you have not been trying to crank the engine too much & done some serious damage .

Might be beneficial to the experienced folks here to know the specific Allis Chalmers tractor model, and which engine you have. I think 1948 AC tractors offered a 3 cylinder gas engine and maybe also a 4 cylinder. I could be wrong, (I often am),...but some of the replies seem to be more for one or two cylinder lawn or garden tractor engines.

Cheak the flywheel if there is some thing stuck on it it will hit in both directions I have torn engines apart because of a loose flywheel bolt be for

kg4ibj said:

Thank you all. I have done all of these steps suggested. As I turned the engine all valves at various times opened and closed so it appears the lifters are not stuck nor a valve staying open. There was no fluid in the cylinders. The only thing I know to do before attempting to find a mechanic, if there is one who will work on this tractor, is to pull the oil pan and look from below. Any other thoughts?

Click to expand...