Ok, after the last posting, I had definitively determined the cause of the oil leak was the hub, and I was awaiting a new o-ring from WhirlWind Propellers. Well, I installed the new o-ring, ran it up, and no leaks. A positive sign. But, to really test it, I needed to fly it. After flight – oil everywhere just like before. At this point I was really perplexed. The entire inside of the flywheel was coated with oil, and it was spraying that oil everywhere. The area by the nose seal remained dry. Perhaps there was a problem with the tolerances of the flange or the prop?

I called WhirlWind Aviation in Ohio. This is the outfit from whom I bought the propeller. The had sent me the new o-rings, so now they were kind enough to send me dimensions and tolerances I could check. In this process, I learned that Whirlwind Aviation is no longer affiliated with WhirlWind Propellers. So I’d have to also talk to WhirlWind Propellers.

I checked all of the clearances. Everything looked perfect. Clean flange. Clean hub. Immaculate o-rings. All specs checked out. I was stumped. I had a couple other RV builders look at it with me. All equally stumped.

I called Jay with Whirlwind Propellers, and he was going to investigate solutions and get back to me. I was convinced it was the prop. That said, it was time to take this mystery back to square one. I started by thoroughly cleaning every single bit of oil from every surface I could get to. Then I added UV dye to the engine oil. I also wrapped several areas in paper towel, and even sandwiched a one-ply layer of paper towel between the flywheel and the flange to look for oil leaks.

I did everything incrementally. First I did a normal 1800 rpm run-up with the engine running for 3 min. I wasn’t expecting much, as previous run-ups never showed oil. It only showed up once I flew it. I put the airplane in the hangar. Turned out all the lights and used a UV pen light to look for oil leaks. Nothing.

Second run up. This time to 2000-2200 RPM for as long as temperatures remained ok. I got about 8 minutes of run-up time. Repeated the procedure. Back in the dark hangar, and checked with a UV light. This time I thought perhaps there was some oil on the engine seam. That was a bit worrying. I cleaned what I saw, so that on the next run-up I could be 100% sure if there was a change.

Another, run-up just like the last one, and back in the hangar. No evidence on this run-up of oil at the seam. Also no real evidence of oil at the hub. I did, however, notice some oil around the prop oil line. I had it wrapped in paper, and I wasn’t sure I was seeing a change, or perhaps just some oil it picked up from residual. I ran it up again, and this time, I was sure there was oil on that paper towel.

The paper towel had a pretty good amount of oil on it. Definitely indicative of a leak. Conclusion – the NPT fitting here is definitely leaking, but could this be the cause of what looked like a hub leak? Would it be possible for this oil to travel from the high pressure area inside the baffles and forward to the flywheel without getting any oil on the area by the nose seal? I was skeptical, but hey this is a leak, lets fix it and see what the result is!

When I pulled the flare fitting off the NPT fitting, the NPT fitting was barely finger tight. I could loosen it with my hand. After removing the NPT fitting, it also appeared that anti-seize had been used instead of Permatex #2 or similar sealant. No wonder it was leaking! And I bet it was leaking really good at max power!!

After removing the NPT fitting I thoroughly cleaned it, applied Permatex #2, and reinstalled. 

After a couple more run-ups… no oil. So it was time to take it flying once again. I had to once again safety wire the prop. Really tied of pulling and reinstalling that prop!

After taking it flying. No oil. Now, several flights later, the engine remains bone dry up front. Problem, at long last, finally solved.

What did I learn? Well I knew the air could make the oil do funny things. And I knew that the oil on the flywheel meant it was making a mess everywhere. But I was still skeptical that the leak was coming from somewhere on the engine and moving forward. So my big takeaway on chasing oil leaks is to start clean, and incrementally step towards finding the exact leak location. I’m a believer in the UV dye. It makes finding oil a no-brainer.