Variocam thoughts and questions

[Homeoboxter]

Ok, so I did my homework and I have read through a a lot of threads and articles on this variocam fail topic and I learnt a few things that were new to me but maybe obvious for most of you all. I still have some questions that I thought are worth to share. First, what I learnt: 1) The actuators are all the same in all 5 chain engines, from 2.5 to 3.4, or at least they have the same part number. 2) The two units are different though, variocam 1-3 and 4-6 move to the opposite direction when they actuate, and it seems only actuator 1-3 has this large green O- ring that has a tendency to disintegrate. At least in all the threads I`ve looked at the first sign was the appearance of green rubber O-ring fragments. Actuator 4-6 has no such large green O-ring shown on the few pictures available on the web.

I noticed that when the actuator is not filled with oil the piston moves freely between the two endpoints. When the camshafts rotate and the valves open and close the load alternates respectively between the small chain`s upper and lower side, resulting in tugging the actuator`s piston between the two end points pretty badly. I uploaded a video of this here:

https://www.youtube.com/watch?v=F069qIpI3_U

When I fill the actuator with oil with a syringe, the piston no longer moves. So I assume the tugging is gone once the actuator is pressurized. Also, normally the oil can`t escape from the actuator easily, because there`s a check valve in the actuator`s oil pressure line which rectifies the oil flow. So, is it possible that the check valve remains open because of dirt or something and the tugging at start up eventually destroys the O-ring?****

In this case, dying of the actuator should be preceded by a rattling noise at every startup. Is that true?

Why is it that only the 1-3 actuator fails (if that`s true)? I`ve read some hints somewhere here on the forum about that in engines with****DOF****where the IMS is punched through, the actuator may be more vulnerable and more likely to fail. This makes sense to me because oil might leak through the IMS at the pump and the oil that gets lost has to be pumped back at startup. So, is there a real statistically significant relationship between DOF and actuator failure? And again, why only actuator 1-3?

Opinions?