After the last update, I had pinned the oil leak on the prop hub and was waiting on a new o-ring from WhirlWind Propellers. Once it arrived, I installed it, ran the engine up—and saw no leaks. A good sign. But to really test it, I needed to fly.
After the flight? Oil everywhere. Just like before.
Now I was seriously perplexed. The entire inside of the flywheel was coated in oil, and it was flinging that mess all over the place. But interestingly, the nose seal area stayed bone dry. I started wondering—could the tolerances on the prop or flange be off?
I called WhirlWind Aviation in Ohio, the shop where I bought the prop. They had already sent me the new o-rings, and now they were kind enough to send specs and tolerances for the hub and flange. That’s also when I learned that WhirlWind Aviation is no longer affiliated with WhirlWind Propellers. So, I now had two different companies to coordinate with.
I checked all the clearances. Everything looked great—clean flange, clean hub, immaculate o-rings, all within spec. I brought in a couple of other RV builders to take a look. All of us were stumped.
Eventually, I got in touch with Jay at WhirlWind Propellers. He said he’d look into it and get back to me. At this point, I still suspected the prop, but I knew it was time to go back to square one.
I cleaned everything—every surface I could reach—until there wasn’t a trace of oil left. Then I added UV dye to the engine oil, wrapped suspect areas in paper towels, and even slipped a one-ply sheet between the flywheel and flange. I wanted to see exactly where the leak was starting.
I took an incremental approach:
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First run-up: 1800 RPM, 3 minutes. No surprise—no leaks. It’s never shown anything unless I actually fly it. Checked in the dark with a UV pen light—nothing.
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Second run-up: 2000–2200 RPM for about 8 minutes, staying within temp limits. Back in the hangar, UV light in hand—I thought I saw oil at the engine case seam. Worrisome. Cleaned it thoroughly for the next run-up to confirm.
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Third run-up: Same as before. This time, no oil at the seam. That was a relief. I did notice something interesting, though: oil on the paper towel I’d wrapped around the prop oil line. It wasn’t clear if it was new or just residual from before.
I ran it again. This time, no doubt—fresh oil on the paper towel. A decent amount too. That line was leaking.
So now the question: could that leak have been the leak? Could oil be moving from inside the baffling, around the nose, and into the flywheel area without touching the nose seal?
It seemed unlikely. But this was a definite leak, so it was worth fixing.
When I pulled the flare fitting off the NPT adapter, I found the NPT fitting was barely finger-tight. I could unscrew it by hand. Worse—whoever installed it had used anti-seize instead of proper sealant like Permatex #2. No wonder it was leaking. And under max power? I bet it was gushing.
I cleaned everything, applied Permatex #2, and reinstalled the fitting.
A couple more run-ups—no oil. So I re-safetied the prop (again—really getting tired of that), and took it flying.
Still no oil.
Now, several flights later, the front of the engine is staying clean and dry. Finally. Problem solved.
Lessons Learned
I’ve always known that airflow can make oil do strange things. And I knew that oil on the flywheel would sling a mess everywhere. But I was skeptical that a leak from somewhere behind the nose could travel forward like this without leaving a trace at the seal.
Turns out, it can.
Big takeaway: start clean, go slow, and isolate everything step by step. The UV dye is worth its weight in gold—it makes tracking leaks straightforward. I’m a convert.