Non-Annual Maintenance

After the big trip to Oshkosh we really haven’t been doing a whole lot of flying lately. We did fly out to Salt Lake City to visit Marissa over Labor Day weekend, and then I ended up back there in the beginning of October. Our rental house there had a water pipe burst and flood the basement with a foot of water. I was able to take off Monday afternoon and get out there in about 3:35 with a nice tailwind. After dealing with water damage companies, plumbers and insurance, I was able to find a weather window on Friday afternoon to head back home.

On the flight back, I had an anomaly with the autopilot Roll servo going offline, and then later getting a Skyview secondary network failure. All of this came and went by itself. After it cleared itself, I was able to use the Autopilot normally. About 30 minutes into the flight, my Primary Flight Display on the Skyview EFIS went blank. The engine and map pages were still up and running. The alert was an ADAHRS FAIL and another secondary network failure. After about 30 seconds, it all came back and was fine for the rest of the flight home.

screenshot-N5771H-SN03222-15.3.4.4867-20181005-112848-166-en_US
Not what you want to see as you are flying.

The weather during the week I was in Utah was rainy and the airplane was tied down outside. I wondered if it could be due to wetness, but I had the canopy covered and it wasn’t wet inside the fuselage.

The next day was the Ramona Air Fair. I was scheduled to fly Young Eagles for EAA Chapter 14. When I got to the airport Saturday morning it was very low IFR conditions and the weather report said that it might clear by 11am. I pulled the airplane out of the hangar and started it up to taxi over to the fuel island. I was low on fuel after the non-stop flight back from Utah. The engine fired right up, but then it really started running roughly. I played with the mixture, thinking it might be a fouled spark plug, and switched the P-Mags from Left to Right and back to Both which made no difference. The CHT/EGT gauge showed that cylinder 3 wasn’t coming up to temps. Then just as fast as it came on, it was back running smoothly and the temps came up. I taxied down to the ramp by the Tower where the Air Fair was going on. There were just a few planes there due to the weather, and I ended up hanging out at the airplane all day talking to people. The weather never really cleared up to more than Marginal VFR. I wasn’t going to fly any Young Eagles unless it was clear VFR weather. No fun to do scud running with other people’s children. Photos from the day are here.

The engine ran fine as I taxied back to the hangar. The next Monday I had to fly up to Fullerton, CA to pick up a friend of my daughter, who was visiting. I fired up the engine and it did just a bit of the same rough running with cylinder #3 showing coolness, then back to running smoothly and warming up. I have to admit a dilemma here on whether to scrub the flight or not. I let the engine warm up, and did a thorough preflight run up or two and everything was running fine. OK, let’s go. The flight up and back was uneventful, with no autopilot or engine issues.

Back home I got down to searching online to see what might be going on with the autopilot and the engine. The consensus on the engine was probably a sticky exhaust valve. Van’s Airforce Forums has plenty of information about how to cure this. There is an excellent writeup by Mike Bullock on how he went through this and was able to ream out the carbon buildup from the valve guide and get the engine running smoothly again.

In order to get access to the valve, you have to compress the valve springs. This requires a special tool, which isn’t cheap. Mike modified a couple of pry bars to make his own home-built valve spring compression tool. I went off to Home Depot and got my own pair of pry bars for less than $15, and went to grinding away various bits to make it work.

I spent all of the next weekend working on the sticky valve. It was definitely stuck. I won’t bore you here with the process, so if you are interested, read Mike’s post above in the link. I did go through all of the cylinders to see if any others were sticky, but they were all smooth. I had to drop the exhaust pipes for access inside the cylinder heads. It took a few days before I could put everything back together since I was short a few lock washers required on the exhaust nuts.

As the plane was just sitting in the hangar, the autopilot roll servo must have just locked itself up without any power on. I noticed this as I was walking around the airplane and I touched the aileron and found it completely stuck in position. I wiggled the aileron and it gave a quite a bit of resistance, until it “popped” and then it was smooth again. Again, back home and searching the internet I determined that it was probably the “shear screw” in the autopilot servo that “popped”. The shear screw is there to break in case the autopilot ever gets stuck. You can overwhelm the autopilot with the stick and shear this little brass screw to regain manual control if needed.

I powered up the Skyview system and went into the Setup and Systems menus to get to the autopilot hardware calibration screen. Moving the stick around showed the pitch servo coordinates moving around, but nothing for the roll servo coordinates. Time to extract the servo from the right wing.

IMG_5977.jpg
Autopilot Roll servo extracted from the wing.

The servo motor was completely locked up and the shear screw was definitely broken. Very strange to have the motor just lock up and I was very glad this didn’t happen while flying. I called up Dynon the next morning and got an RMA number to send the servo back for a rebuild. Since it was long out of warranty, they will rebuild it for a flat fee of $175. From looking online at the Dynon Forums, other people have had this happen, and it looks like the servo might have caused the issue with the secondary network and the previous ADAHRS FAIL issue. The Autopilot servos are also on the same network. The network has a redundant pair of network wires, so there is a primary and secondary path for the network.

The other thing going on with the airplane is an update to the ADS-B unit. Dynon originally provided an ADS-B unit SV-ADSB-470 which had just weather and traffic input from ground stations. They later came out with an updated unit SV-ADSB-472 which also can get traffic input from other ADS-B equipped aircraft without needing proximity to a ground station. The initial 470 units from Dynon had some limitations, and this was going to be fixed with the 472 units. Dynon announced back in early 2017 that they would have a trade in program for owners of the 470 units. However, the early 472 units had some hardware issues. Here we are a year and a half later and the updated 472 units are fixed now and back shipping. Dynon called me this week and asked if I still wanted to trade-in the old for the new unit. I said yes, so they are charging me $308 for the new unit (saving $500 for the cost of a new unit) and I have to mail them back the old unit within 30 days. Now I get to crawl back into the rear fuselage and swap out these units.

Lastly, since the airplane is grounded, I might as well also get my new tires mounted. The front nose wheel steering break out forces also seems to have gone up recently, so I need to take that all apart and get it re-lubed up and the force on the fork set correctly.

I also dropped off the Oxygen tank for a refill. We went through most of the O2 on the trips to and from Utah. The second trip out there I was up high at 15,500′ getting pushed along by some strong tailwinds. You can’t do that high flying without supplemental oxygen.

I’m hoping to be back flying again soon! I’ve got a few trips planned in the coming months.

2 thoughts on “Non-Annual Maintenance”

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