I wanted to test the nose gear retraction system and get the actuator limits set correctly prior to moving on to other things. Instead of hooking up the hydraulic pump and having to potentially chase hydraulic fluid leaks, I decided to use gas. Yes, there is a stored energy concern compared to using hydraulic fluid, but its still a good first test if I am careful. I got a nitrogen cylinder and a regulator and hooked it up to retract the nose gear. The actuator brought the mechanism out of over-center at about 200 psi, and at about 300 psi, the gear quickly sprung all the way up. After closing the nitrogen cylinder valve, the pressure quickly decreased and the gear fell back into the extended position – clearly a leak somewhere. I got some snoop (soapy water) and started checking fittings but it became pretty clear that the external fittings were not leaking but the actuator cylinder was leaking internally. This discovery made the test worthwhile.
I removed the nose gear actuator cylinder (PITA) from the keel, disassembled it, and found that the actuator piston o-ring and backer ring were deformed, “rolled”, and torn. Although the actuator had oil in it, and moved easily, it looked like the piston had been inserted dry during initial assembly. The end piece o-rings and backers were in good shape, but I will replace them anyway during rebuild.