Nose gear up lock assembly

GMPoland · #1 11-16-16, 11:50 AM

Upon reassembly of a nose gear up lock actuator on a 65 SN 0127 with new o rings it was exceptionally difficult to move the shaft. O ring from Parts manual Fig 122A item 7 Pn AN 6227B11. seems to be the culprit. Question 1 is upon reassembly how much pressure should it take to move shaft? Question 2 is will hydraulic pressure overcome this force in normal operation? Service manual give spring compression levels disassembled but nothing is mentioned about the assembled force required to move the actuator. References from Service Manual were Pg 5-19 para 5-28-30

JAG · #2 11-21-16, 01:00 PM

Not sure about your questions, but it does not sound right to me either. What did you pre-lube the o-rings with?
JAG

GMPoland · #3 11-21-16, 08:20 PM

After several disassembly and reassembly events using 5606 as well as petrolatum. We discovered a very slight difference in thickness of the oring pn 6277B11. Opened a different package and tried it. Works good now. Might have been a manufacturing error or packaging. Seems to function freely now with the internal spring pressure adequate to push piston back out. I didn't measure the differance but it was obvious when the two were compared. Opened a third correct pn oring just to make sure. What a pain. Getting up on jacks now to perform retract/extension check. Different orings did not work see next reply!

GMPoland · #4 12-20-16, 09:39 PM

Upon several assembly and disassembly attempts with the same result. Gear would retract completely then not extend as the nose gear would not unlock. Had to manually reach into compartment with pry bar and assist nose gear uplock to disengage as it was frozen or stuck. We could only get actuator to function normally with the one size smaller- 10 oring. Not being satisfied with this we called the Cessna sevce rep and got the dimensions for the grove in the actuators shaft. It was undersized dramatically. A quick turn on the lathe to the correct grove size. And reassembly with correct o-ring and teflon split washer and actuator functions as it should. Performed many gear extension and retract tests with drill driving hydraulic pump and no issues.
So this issue could be problematic for other aircraft. Cessna service center and the Rep we talked to was very helpful. This actuator has no documentation about repair In my logs so I can only assume it has functioned like this for years. We only discovered this when rebuilding some of the gear door actuators and the unlocks to stop a few leaks.