Firstymar, the short and useless answer is to not use ether because it will break stuff. That's not really an explanation though.
Diesels work by compressing air to a tremendous pressure, then injecting a tiny amount of fuel into the cylinder while the air is compressed and thus heated up. That heat auto-ignites the fuel. It burns, producing expanding gas, providing the force to drive the piston back down. The fuel is injected into the combustion area of the cylinder, not into an intake manifold like in a gasoline engine. In other words, the intake manifold and valves are dry.
Once you understand how the engines work, you can see why it is dangerous to use starting fluid. The fuel has to be injected late in the compression stroke, so that it ignites late enough to not be fighting the piston's upward stroke, trying to run the engine backwards.
Ether is used because it is extremely flammable. That is, it ignites easily. That's why it works in a gas engine. Diesel is much tougher to light in comparison.
So, here's the danger: In these little engines, the amount of fuel burned at each cycle is minute. Think about it: when running at 2400 rpm, a two cylinder engine in a tractor is pulsing 20 times each second. In an entire minute, the injectors have fired 1200 times. If you run your tractor for minute, can you even detect any change in the level of the fuel? It's a tiny amount in each pulse.
Compare that to how much starter fluid the normal person will dose their machine with. A brief pop of the button is likely more ether than the diesel tractor consumes in a minute of running at high rpm.
That is our dangerous situation: Way too much fuel that is much more easily burned than diesel. It's also being introduced at the wrong time, that is, at the beginning of the compression stroke. Set it up: Diesel has to be injected late in the compression stroke or it will auto ignite. Diesel is much more resistant to auto-ignition than ether, and ignites at higher temperatures. Ether has been introduced in much higher quantities than diesel would be, and as early as is possible in the compression stroke. A worse scenario isn't possible, really.
When the piston compresses the mixture of ether and air, it will auto ignite, but much too early. With the piston going one way, and the exploding ether going the other, something has to give. It may be a head gasket, the rings, the piston itself, a rod bending, or whatever the weakest point is at that moment.
Some heavy equipment has built in ether injection. So far as I or anybody else I've talked to has seen, these are all very large engines in comparison to our tiny engines, making the dose of ether much smaller in comparison. Larger engines also have more room to absorb the stresses.
I have used ether on diesels before, even little ones. I shouldn't, but have. Here is what I was taught: when using it, you want to give the tractor a "smell" of it. Think about the amount of ether it takes for you to be able to detect it through smell. That's how much you want to give.
Get the engine cranking, then give as brief a spurt as you can from the can away from the air intake, then sweep it across the intake as you do it. That sends just a tiny amount of vapor into the engine.
A caveat: None of my Yanmar machines have functioning Thermostarts in the first place. I also don't use or need ether on them. Same with glow plugged machines. The glow plug works by getting super hot-hot enough to make metal glow. Spraying ether down the gullet of something with the glow plugs or thermostart on will likely result in a terrifying fireball and/or explosion. So don't do that.
The tiny amount of ether that makes it through the air intake, filter and intake manifold is enough to burn, but not as violently explode as a spray of ether directly into the manifold will do. All I'm interested in is getting a tiny bit of extra heat in the system to help the diesel ignite. Sometimes it takes a couple sprays to get it to work, but I'm patient and take my time.
A better way to do it is use a block heater for a few hours, or use a hair dryer or shop light to pre-warm the intake and cylinder head, then run hot air through the intake with the hair dryer while it cranks. A battery booster set to "start" often does the trick alone. Pull-starting with a car or tractor will also work. Ether is a last-ditch, emergency device on little diesels, in my opinion. An engine that's refusing to start has issues to be addressed, barring environmental conditions far out of normal. Even then, it makes more sense to address those (by heating elements or what have you) than to risk damage to the engine.
I'm glad you got your tractor running!
