bdash

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About bdash

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    Advanced Member

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  • Gender
    Male
  • Location
    Lakeport, CA
  • Reg #
    N335BB
  • Model
    M20J

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  1. To circle back on this: I asked that the cylinder be borescoped before proceeding. That revealed vertical scoring on the cylinder walls, consistent with broken rings, so I ended up replacing the cylinder. I’ve flown around three hours since, and am still waiting on signs that the rings have seated. The weather’s looking rough for the foreseeable future so it’ll be at least another week until I’m truly back up and running.
  2. The sticky exhaust valve was said to be the cause of the EGT drop that led to me taking the aircraft into the shop. The low compression was something additional that the shop reported seeing while investigating the issue. Right, if something went awry very recently I'd have not had time to notice a change in oil consumption. Would something like a broken ring be visible in any form in the engine monitor data?
  3. My understanding is that the sawtooth EGT pattern, as well as the asymmetric pattern on the exhaust valve when looking via a borescope, is due to an exhaust valve that's leaking due to erosion after uneven heating, rather than one that's sticking. I haven't seen any pattern in the EGT data to suggest that uneven heating is the issue. That said, borescoping is what I've requested as the next step to see if there's anything wonky with the valve or if it's just a matter of reaming the valve guide, and to see if the cylinder walls show any signs of ring problems.
  4. The potential extra cost, along with the extra time waiting for the airport to re-open, is part of my dilemma with taking that approach. I'd expect something like a broken piston ring, or any high amount of leakage past the rings, to have resulted in increased oil consumption and blow-by. I've not observed any of those things. That's one reason the reported low compression is so puzzling to me.
  5. Major overhaul was about 750 hours ago. All four cylinders were replaced by the previous owner around 200 hours ago (3.5 years).
  6. Contintental's SB03-3 has very detailed guidance about compression tests on their engines. If the compression test reads below their leakage threshold, boroscope the cylinder, and if all looks normal then fly at 75% power for at least 45 minutes before testing compression again. Lycoming's guidance is much less detailed.
  7. During my last flight in my M20J, I noticed a slight roughness that corresponded to a drop in the EGT of cylinder #4 by around 60º. This lasted for 10-15 minutes, went away for a few minutes, then came back for the remaining 5 minutes until I landed. I downloaded the engine monitor data after flight, and it showed the change in EGT very clearly. Looking back over data for previous flights I haven't seen any similar change, or anything else out of the ordinary. So I took the airplane over to my local shop. They did some investigation, and reported back that the underlying problem is an intermittently sticking exhaust valve. That seems to line up with engine monitor data. From some research, addressing this typically involve cleaning the exhaust valve guides. However, the shop reported that as part of their diagnostic process they performed a compression test and cylinder #4 came back with a very low compression reading (< 20/80) due to leakage past the piston rings, and because of this they're saying the cylinder needs to be removed and either overhauled or replaced. The engine was developing full power during the last flight and, with the exception of the EGT drop in the most recent flight, all other data related to the cylinder looks normal and hasn't changed since the annual inspection (at a different shop) around 3 months ago when the compression was in the 70s. One confounding factor here is that the local airport currently has both runway and taxiway closed due to resurfacing, so any engine warm-up prior to the compression test they performed would have been done via a static run-up. Advice I've seen about low compression numbers has been to fly the airplane until everything is up to operating temperatures and re-test, but that won't be possible until the airport reopens in mid-November. Does this warrant pulling the cylinder and overhauling / replacing it, or is there further investigation that should be performed before going down that path? My inclination would be to clean the exhaust valve guides, fly the airplane for an hour or so, and perform a compression test immediately afterwards, on the assumption that the low reading is an artifact of testing rather than an actual problem. But if the likely outcome of this is that the cylinder comes off anyway, that's just extra cost and time wasted.
  8. Took my wife and daughter down to Nut Tree (KVCB, Vacaville, CA) for brunch at Fenton's Creamery this morning. The little one rode up front for the first time, and had SO MANY questions about the airplane once we were home (What was that black knob for? What does the orange button do (CO alarm)? What are all the other buttons for? On and on and on until bedtime). She's been telling us she's going to be a pilot when she grows up since before I took my discovery flight. The only downside at all about our flight today was that it was 95º out. That made for a sweaty time on the ground while we got loaded in and through the run-up. It might be time to look into one of those ice-chest-based coolers I've seen mentioned.
  9. Would you mind sharing which CFI you fly with out of Lampson? I did all of my primary training over in Ukiah, and have done a little work towards my instrument rating while down in the Bay Area for work, but have never run into a CFI while at Lampson. I’m sure there are some lurking around here somewhere. It’d be nice to have a local option.
  10. Merely renting out an aircraft isn't classified as operating "for hire", so 100 hour inspections and such aren't required unless you were also providing flight instruction in the aircraft, or the renter was being paid to carry passengers.
  11. I had a Tempest fine wire plug lose its center electrode a couple of weeks ago. I initially noticed it only as higher than normal EGT on one cylinder during cruise, but a mag check once on the ground showed the engine running incredibly rough on the right magneto. That narrowed things down. I had a mechanic pull the spark plug in question and we were shocked to discover the center electrode missing. We replaced the plug with a Champion fine wire plug because that's what they had available. Interesting to hear that this seems to be a somewhat common failure mode for the Tempest fine wire spark plugs.
  12. I'm the one who was lucky enough to end up with Bennett's aircraft. Dan at LASAR, the head of parts, is a friend of mine, and he knew I'd been shopping for a M20J for a few months (including sending one to LASAR for a PPI that ended up showing unexpected corrosion). Bennett's Mooney was in at LASAR getting an annual inspection done when he made the decision to part ways with it. He mentioned to Dan that he'd likely be sending it down to All American Aircraft when the annual was complete. I gave Bennett a call, we chatted a while, and put together a deal. He was generous enough to have me come by his hangar after the sale closed to pass on a portable O2 system, spare parts, extra headsets, etc., that he no longer needs. A very kind soul.
  13. The G3X maintenance manual says: Standby attitude, airspeed, and altitude instruments are required if a G3X display unit is installed as the primary flight display (PFD) in IFR installations. The standby instruments may be a Garmin G5 or existing pneumatic instruments.
  14. You’re correct. It’s specifically the GDL88 that the installation manual calls out as being incompatible. It does note that a GDL 88 can continue to provide weather and traffic to GTN units, it just won’t appear on the G3X.
  15. Two limitations I see with the G3X vs the G500 as it currently stands: The GAD43 autopilot adapter does not appear to be supported by the G3X, meaning that folks with attitude-based autopilots such as the KFC 150 will need to keep their vacuum-driven attitude indicator to drive their autopilot. The GDL88 is not supported by the G3X, meaning traffic and weather will not be displayed on the G3X.