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. 

So I’ve been noticing, since day one really, that my oil pressures have been on the low side. Lycoming has the green arc for normal operating pressures between 55 and 95psi. However, my plane was operating in the mid-40s to low 50’s at cruise power settings. Granted, it has been very hot outside, but still lower than I would like. Here in the first graph you can see my oil pressure and oil temps during a recent break-in flight.

Luckily, oil pressure is adjustable. Lycoming has three types of oil pressure relief valves. All work by tensioning a spring against a large ball bearing that controls the pressure. The most modern, is a fully adjustable valve that has a nut you can turn to adjust pressure. Then there are two non-adjustable valves. A short and a long tower valve. I have the long tower non-adjustable. Non-adjustable doesn’t mean you can’t adjust it, you just can’t do so by turning a setting. These valves are adjusted by way of either a different tension / length spring, and / or placing washers under the spring to shim it and increase tension.

Here is some guidance I gathered from a couple places on the web:

There are also springs of varying tensions and lengths which can be interchanged if the above adjustments do not yield the desired results. Some of the springs are color-coded to help differentiate them from one another. The most commonly used ones are the white LW-11713 springs (thick, heavy springs that are used to increase oil pressure at all settings), the 68668 (purple springs that are short and have much less tension than the others), and the 61084 non-color-coded spring that is standard equipment on most regulators.

Longest and shortest spring doesn’t equal toughest and weakest springs. as you can see the toughest spring is the second to shortest. and that spring is a really, really, high tension spring compared to any of the others.

Highest tension to lowest are:

• LW-18085 1.93 inches free length
• LW-11716 2.12″ (White)
• 61084 2.18″ (Most common spring) (No color)
• 68668 2.04″ (Purple)
• 77467 1.90″

Use the 61084 spring with an adjustable tower or a tall tower and a 68668 with a short tower. Use the 77467 in a short tower if you can’t get the op low enough even without adjusting washers and using the spacer with two gaskets. That was my starting points and worked out really good 99% of the time. You should never need to use the top two springs in any normally aspirated engines.

When I took mine apart, I discovered it had a purple spring. Which, as you can see from the above is one of the lowest tensioned springs, and normally for use in the short valve towers. Mine already had three washers present, and I added 3 more. The results you can see below. A little more pressure, but not great. My assessment was, that 9 washers (the maximum) was unlikely to get me the results I wanted, so best to get a new spring.

I got a new spring (two actually), the LW-11716 2.12″ (White), and the 61084 2.18″ (Most common spring) (No color). I decided to install the one with no color since it is the most common. I sat it next to the existing spring with 6 washers, and decided to make it the same length, so I added 2 shim washers. The resulting oil pressure is now within the green arc, but barely.

So I added two more washers, and now I’m pretty comfortably in the green arc. Temperatures in Maryland are in the 90’s at the moment, so oil temps are probably a little high, and thus oil pressure a little lower. I could probably add another couple washers to center the oil pressure a bit more squarely in the green arc, but I’m going to just fly it for a little and observe for awhile before doing so.

The procedures for this adjustment couldn’t be simpler. All you need are a couple AN900-20 crush washers, some washers, possibly a new spring if needed, and some safety wire.

Here is the relief valve on the engine on top of and behind cylinder #3. You couldn’t get any easier access!

Here is the valve removed. I just left the ball bearing in place for most swaps.

And finally, what the tower looks like when removed. For returning the spring and tower to the engine, I just sit the ball bearing inside, and then push it back into position with the spring as I seat the tower. Even with safety wiring, it is a 5 min job.