Oil leaks, fittings and hoses
Here is a dumb question I expect to go unanswered. What do I need to know about (both ends of) flare to hose fittings and which are best? I ask for several reasons, mostly for the oil system, but I think this applies to fuel as well. I am having a tough time stopping an oil leak at my new Earl’s oil cooler with AN-10 O-ring to AN-8 flare adapters (I don’t think it is leaking at the O-ring, but I notice that the next bigger O-ring would still be snug and fit). Dell aluminum flare fitting seals from Aircraft Spruce are not helping, if the leak is at the flare. It is not a big leak, but over time it is making a mess and might introduce air if I let the plane sit too long, requiring purge.
Discussion. AN Aircraft Flare fittings have a 37 degree flare angle (and I have a flare tool that makes this), whereas industrial fittings have a 45 degree angle (and I have a flare tool for this as well), and I see pictures of a mix on some installations (brass industrial mated with painted AN). Is this ok? Also, for the hose connections, I see pictures where some people use clamps (Oetiker, worm gear, or fuel injection), some do not. It appears some are pushed on (push lok?), and some are screwed using a left hand threaded nut and right hand thread barrel with the hose sandwiched between. Do the push lok and threaded style work well without any clamps (or indeed not supposed to use clamps), and how must they be sized to fit 12.5mm Parker hose (inside and outside diameter for the sandwiched style)? Can I apply lubricant to help get the hose to fitting installed? Heat (boiling water or heat gun?)? Do some barbed hose fitting require clamps (like the idustrial ones with rounded barbs), and some specifically not use them?
And then, if we use clamps, the fire sleeve does not fit. Or the band-it clamp would crush the Oetiker clamp if we are not careful. What then? Put the band-it further away from the clamp, up on the hose, while stopping short of crushing the hose, leaving a loose band-it clamp?
Why do many automotive AN fittings have a hole in the side of the flare nut (showing a shiny piece of metal – and this is most of them)? Are they as good as the heavier Rotax originals without the hole in the flare nut, and what is the purpose of the hole in the side of the nut? I admit, torqued one down so hard trying to stop my oil leak, it popped apart and I see a retainer ring. Fortunately the flare nut popped apart on the ground.
Sorry for making so much an issue of what apparently is only a problem for me. I could not find any such discussion.