The needle valve seat is screwed in.
Then the needle valve itself is screwed in place.
The new valve spec requires that a different valve washer stack be used. The proper washer shims are pulled from stock.
The shim stacks are placed on both sides of the piston valve body according to the BOM. A new bearing has also been installed on the outside of the piston valve body.
The assembly is carefully sprayed off with solvent to make sure its perfectly clean before being tightened down.
Thread locker is applied to the threads to make certain that the piston won't unscrew itself from the shaft.
The nut holding it all together is applied and tightened down.