I replaced my pump pistons in 2012 and got the same type of replacement pistons with the extra piece. Those pistons also fit a Ferguson hydraulic pump and I have been told that those pumps use a guide rod to help keep the pistons in line. They are not used in the 8N pump. I just pointed mine down. Just make sure they clear the bottom of the pump chassis. I slathered the bushings with oil before assembly, just to make sure they had a light coating before trying to start. I also pre-oiled everything I could get to in the pump, just in case. I think the bushings have enough clearance to pull in a little oil as they move back and forth.
I found that my old valve springs were stronger than the replacement springs so I used the old ones. My logic was that since the spring is used to force the valves closed once the pump pressure is diminished, stronger springs would probably help keep pressure in the system. My rebuilt pump works great now.
Here is a link to my question on the valve springs:Hydraulic Pump Valve Springs
Hope this helps.
Jimps in GA. This post was edited by Jimps at 09:55:20 01/03/14 2 times.