When you travel abroad and come across an unfamiliar power socket, you still know how to use the respective plug, because a plug is a plug, no matter how you look at it. But what if you have never seen an electric socket before?.. Made you think, didn't I?
The same can be applied to hydraulic components. People who overhaul hydraulic pumps and motors regularly have a well-formed idea of how components work together and what they look like, and if they came across "shuffled" parts of an unknown, let's say, axial piston motor, they would still be able to combine them into a working assembly. But if you have never seen an open hydraulic motor before, you are guaranteed to assemble it "less than 100% correctly". Even if you know how hydraulic motors work!
Let me ask you a question - have you ever wondered what could happen if you did something prohibitively wrong while assembling an axial unit, like, say, mounted the valve plate upside down? Of course, for most pumps and motors it is physically impossible due to the unilateral fit of the valve plate, but there are motors (like the Kawasaki M2X170 presented here) that allow the valve plate to be mounted in two manners. Of course, only one of them is correct... I bet many experienced overhaulers thought about this, but, naturally, could never afford to get the answer. How nice it is then, that there are so many "free spirits" willing to try their luck assembling stuff they know nothing about to get us the answers we crave!
Take a look at this picture. The valve plate. Yes, that's right, the bronze side, instead of facing the camera, should be facing the cylinder block! It is also interesting to see how the bronze side of the valve plate (that is facing the end plate now) was "embedding" tiny steel particles in it.
The cylinder block sealing face lost about 2 mm of material before the motor ceased completely. And the machine ran for a complete month!