Lubing 108-2 Landing Gear
I'm replacing the belly panels on Da Liddle Birdie (108-2) because they're cracked and the spot-welded pitch link cover was in serious danger of separating in flight (accumulating broken spot welds).
So while I'm under the aircraft anyway, it's time to lube the main gear trunnions. Aside from the fitting being unnecessarily difficult to get at, I managed to dump a complete new tube of grease through the right-hand leg's Zerk fitting - and saw NOTHING coming out either end of the trunnion tube. There should be (I think) wads of grease EVERYWHERE around the trunnion tube ends; the (right-hand) brake torque tubes certainly spewed grease out either end, with only a small volume of new grease injected....
I THINK I have just attempted to fill up the landing gear leg with Shell 33 grease, but that seems pretty pointless. Is there an intentional path for excess grease to enter the leg? Do I have a serious landing gear problem? Has anyone seen anything like this before?
I'm working on my gear legs right now. The tube where the PIN goes through is solid so the zero should only be injecting into the pin and the tube.
The Zerk fitting is (approximately) at the white arrow (hidden on the inboard side of the strut). I would expect that grease pumped in here would eventually exit at the red arrows, in the gap between the inside of the visible tube, and the pin that goes through this tube. The two tube ends are visible (I can get my fingers on them, just) when the landing gear fairings are removed, but I don't see any grease oozing out. And this pivot tube would not hold a complete grease cartridge contents, even if the pin were not installed.
The grease gun is definitely empty - I had to pull the spring plunger all the way back to get a new cartridge into the gun, and the plunger is now fully retracted into the cartridge cylinder. I doubt I got an imperfectly-filled cartidge (weight about right, seal unbroken), so I'm now wondering where the hell all the grease went....?
Additional thought - does the diagonal brace tube on the forward side of the leg open into the horizontal pivot tube and the main leg strut? A place for the grease to divert to if it can't flow out to the pivot tube ends?
I will be at the hangar on Sunday, and I will take a picture inside, but I think the brass bushing goes all the way through.
Thanks very much for the video; it clarifies the internal structure of the gear leg nicely. And convincingly shoots down my speculation.
In the meantime, I have figured out what the problem really was - it's time to throw away the coupling on the end of my grease gun's hose. The [expletive deleted] thing will not lock onto the Zerk fitting ball without screwing its outer casing down towards the hose. This locks it onto the ball, but it also collapses a little spring-loaded rubber fitting inside the coupling to the point where it will not pass grease. There doesn't seem to be a "magic number" of turns on the thread, either - it's grip or no grip / no grease or grease everywhere but where you want it. Your choice.
I finally snagged my hangar buddy's beat-up decades-old grease gun (he's an aircraft mechanic-turned-727 captain, now retired), and the gear lubed just fine. Swapping couplings between the grease guns moved the problem around, repeatably.
The coupler I was initially using is a new fitting, from Princess Auto (kinda like Harbour Freight in the USA), but it is of Chinese manufacture, and possibly is just a metric "equivalent" of an old (real SAE) Zerk fitting? If so, "close enough" (i.e., typical Chinese manufacturing standard... ... on a good day) actually isn't close enough. It isn't even anywhere close. But with a house brand name of "Power Fist", I guess I should have known better.
Again, thanks for the video - it's a keeper.