I finally received the main landing gear hydraulic cylinder from the factory, over a year late. It was installed in the keel tunnel and the retraction cables were attached to the MLG over-center mechanism. Instead of hooking up the hydraulic pump, I decided to use nitrogen to test the retraction. There is a stored energy problem with using gas, so I was very careful to manually help the retraction through the portions that required the most pressure. I found that the over-center lock bar disengaged at about 380 psi, but it only required about 100 psi to hold the MLG in the retracted (up) position.