blown head gasket on 9N?

Would are the most obvious symptoms of a blown head gasket?

wildly varied compression readings, water or antifreeze in the oil pan.

Oil in antifreeze is another symptom

Fill radiator to brim, leave cap off....start and run. If air bubbles show up, probably head gasket.
Also with radiator full, cap off, speed engine up to fill speed, then pull throttle
quickly back to idle. If it spews/blows water out of radiator, head gasket or cracked head.
BE SURE TO STAND BACK FROM THE RADIATOR WHEN YOU DO THIS!!!!!
IT CAN SPEW/BLOW VIOLENTLY!!!

Many things.
Lack of power due to being blown between cylinder but not into the water jacket.
Antifreeze in the oil.
Seeing oil/gas/antifreeze seeping out from around the head.

Oil in the coolant is a lot less likely due the pressure in the cooling system plus most cooling system appear to have a little oil in them any how

Wheat, never heard of using the full speed to idle method to diagnose a head gasket. Inquiring minds want to know what in theory causes this reaction? I can see that acceleration of the engine may increase cylinder pressure and push more compression pressure into the cooling system. But I would think you would see the same result whether the engine was left at full throttle or returned to idle. Just wondering what the thought process is?

I don't know either, but I've seen it work a few times.
It may have ben done on a diesel.

Head gasket symptoms can vary, and be difficult to diagnose in the early stages.

Usually the earliest symptom will be milky condensation under the oil cap, in the
dipstick tube, and inside the crankcase breather tube. But that can also be
caused by short run times and open/missing thermostat.

Mystery coolant loss. No observable leak but coolant level drops regularly.

As the condition worsens, and that is typically how it happens, a progressively
worsening condition, more symptoms will begin to show. Misfire, usually on start
up, coolant or excess steam out the exhaust even on a warm day, blowing coolant
out the radiator even before the engine is hot, unusual overheating, liquid
locked engine (engine hits a hard stop when trying to crank), serious coolant
contamination in the oil.

At that point, it will be obvious there is a real problem.

Testing, there is a 'combustion leak' test that detects combustion gasses in the
cooling system. It uses a chemical that changes color if combustion gasses are
detected in the radiator.

A simple (but not always accurate test in the beginning of the leak) is to fill
the radiator, let the engine sit overnight, pull the plugs, spin the engine
through and watch for coolant to blow out the plug holes. If coolant blows, there
is a major leak. But it may not always detect a very small leak.

A compression test will show a major leak if the gasket is blown badly between
cylinders. Two adjoining cylinders with low or no compression indicate this. Of
course this would be associated with major power loss. It is possible to have
this type failure and not have coolant loss or overheating.

If there is a gasket problem, the sooner it is repaired the better. Continued use
will eventually cause serious engine damage. Letting it sit with coolant or water
in the cylinders and crankcase is not good!

The guys have given you good advice on how to determine that.
But, what are your symptoms that make you suspect a head gasket?
And, if the symptons are bad enough, why not just replace it?
They're [b:2a56644d37]$10[/b:2a56644d37]. Way cheaper than allowing other damage to occur.