Also, please let me know if I have this right...
This is the part that goes in the injection pump?
View attachment 2714
This part is what goes into the head?
View attachment 2715
Your questions suggest that you may be a little out of your depth here.
For that matter, I also may be out of my arena to respond, I have almost no experience with Kubota products, but for a time, I was a fuel injection "specialist" for a Caterpillar dealer. ( don't get too impressed, they only trained employees in one part of the process to cut down on "poaching" by competitors & customers.)
The part that goes in the cylinder head would commonly be called the "injector" or "nozzle".
The shorter part , that ( here my ignorance of the product really stands out ...) goes into the pump body on "Bosch type" or in some machines into the engine block itself, might be referred to as the "pump" or " plunger & barrel".
Now, _why_ does your injector need replacing? Is the cylinder misfiring?
From your other posts, you mentioned white smoke at Idle, perhaps your injector is leaking, constant dribble into the cylinder? ( very bad for the cylinder walls! washes away the lubricant).
I will speculate that the reason to replace in sets has to do with orifice wear ... as fuel is forced through the nozzle to spray into the cylinder, the orifices wear, and get bigger, allowing more fuel than specified to be injected into the cylinders. We used to joke that the ( industry where they always wanted us to "turn the horsepower up" ) would pay extra for these worn injectors. So if a new injector was swapped into a set of used (worn) injectors, that cylinder would then be "weaker" than the others, because it did not inject the additional fuel that the others did. Also if one injector failed, the others might be about to fail, we would not want to get an additional downtime event for the same problem on each cylinder.
In practice, if the injector "pop tested" good, sprayed from all orifices, did not leak from the nozzle end (at specified pressue for specified time), popped-(sprayed) in the correct pressure range & "leak-down" was within spec, we reused the injector.
Any high or low horsepower issues were dealt with by adjusting the fuel settings during engine dyno session.
Often, an injector that failed the initial pop test could be "flushed out" with several energetic strokes on the pop tester handle. ( we were not encouraged to do this)
If the plunger & barrel is the problem ... I am not familiar with the Kubota parts here at all. But perhaps if the design allows leakage into the engine lubricating oil, that is an obvious end result.
Some designs lubricated with fuel, the injectors themselves would not dilute engine oil, but might have trouble pumping enough fuel to start the engine. Generally, if one pump were worn enough to cause a problem, they would all be out of spec & need to be replaced.
Good luck with your machine. CE
