PT20J

This major/minor/STC/337 stuff has been debated forever. But to me, the simplest thing to do is just file a 337. It's only a piece of paper and if you file it no one will ever question it. It also provides backup documentation if the logbooks are ever lost. I just don't see a downside. Skip

This is interesting. I just looked at the schematic for 25-0002 thru 25-0171 (the first batch of 231s which should all be 12V) and it shows an AUX bus breaker and a normally closed radio relay. I did not trace all the wires to be certain that the relay is powered through the AUX bus, but as that was standard practice, I'm reasonably certain that it is. The AUX bus is the circuit that feeds the breaker switches at the bottom of the pilot's instrument panel (landing lights, strobes, nav lights, boost pump, pitot heat, etc.). The purpose of the aux breaker is to protect the power wire between the main bus and the aux bus. Perhaps someone rewired this ship at some point?

Good point. In mine, I noticed that the primer was not sprayed into the gaps between some gussets and the tubes and here was light corrosion there which I removed and treated with epoxy primer.

The main corrosion concern if you keep it outside is to make sure it doesn’t leak water. Good door seals and especially the pilot’s window seal are important. If the pilot’s window leaks on older Mooneys, the water pools up in a channel PK-screwed to the tubular structure and rusts out the screws and then gets inside the tubes and gravity takes it to the bottom tube where it rusts that tube from the inside. Also, if it still has the fiberglass insulation, that will hold water against the tubes and rust them from the outside. If it hasn’t already been done, I’d do SB 208. Older Mooneys had zinc chromate primed tubular structure which is more easily corroded from the outside than the epoxy primer Mooney started using in the 1980s. Skip

Batteries lose capacity (amp hours) long before they won’t run the starter or they fail to hold a charge. Aircraft batteries are considered unairworthy when they fail a capacity test as specified by the manufacturer. So, unless that battery suffered a sudden failure, it has likely been unairworthy for a long time. If you fly IFR, you really should get a capacity test done annually.

I'd have to check the schematics, but I'd be amazed if 1980 Ks didn't all have an AUX Bus. My 78 J had one.

I owned a ‘78 J for 7 years and it sat outside in San Jose CA 50 minutes from my house. I have owned my current ‘94 J for 5 years and it is in a hangar 15 minutes from my home. I haven’t noticed any difference in maintenance costs. The hangar is nice, but I notice that I fly more when the airplane is closer. I do a lot of my own maintenance, so having a hangar is great for that and a consideration depending on how much work you plan to do yourself.

There should be a small weep hole at the low point of the line to drain moisture.

Leaning for taxi became all the rage when 80 octane went away and lower compression engines had to use 100LL. The extra lead combined with combustion chamber temperatures too low at low power to activate the lead scavenger led to fouled plugs. The purpose of leaning is to raise the combustion temperature to better scavenge the lead. An engine designed for 100 octane shouldn’t have a problem running rich during taxi. Leaning doesn’t hurt, but it’s a good way to kill a turbocharged engine if you forget to set it back to full rich before takeoff. Skip

I’m guessing the inboards are harder to find because they get ground up in gear up landings.

It's like the old Brylcreem commercials: A little dab'l do ya. sbm20-229a.pdf

At the museum when we would get an overhauled cylinder it would come with piston and rings installed. We would pull the piston out far enough to install the wrist pin and then bolt it on. The theory is that if you buy an overhauled engine, you don't take it to pieces to measure everything, so why would you do that for an overhauled cylinder?

No. You should probably have an A&P do this.

IO&AIO-360 Parts Catalog PC-406-1.pdf

Porting and polishing helps the engine breathe better which means that you can burn more fuel to produce more power because there is more oxygen in the cylinder on each intake stroke.

A quick Google search for mooney flap hinge covers turns up several at salvage places.

From the PPG technical data sheet... PR1422 Class B is an aircraft integral fuel tank sealant. It has a service temperature range from -65F to 250F with intermittent excursions up to 275F.

Is yours not repairable?

Lycoming SI 1059E has all the approved assembly lubricants.

Yes, they all use the same disks, but the weights are not the same. It’s easy to check the fuel caps for leakage and should be done every annual. Just get a length of vinyl tubing that fits over the vent tube and blow into it (with your mouth, not shop air) while spraying the caps with soapy water and check for bubbles. Switch the o-rings to fluorosilicone(blue) and avoid the annual replacement expense. Lube the center post with Tri-flow and the big o-ring with Vaseline and they will be easy to remove.

The Lycoming build-up lubricant is 15% STP and 85% SAE 50 non-detergent oil. Lycoming approved case half sealants are RTV-102 or Loctite 515 per SI 1125D

Bladders are made from an entirely different material than sealants, so it's apples and oranges. Fuel tank sealant products generally tout their resistance to hydrocarbons because fuel is a strong solvent. It stands to reason that if they can withstand soaking in gas, they can withstand air and heat. The application is critical. I have a 30-year-old airplane that has no leaks. Maybe I got lucky and my airplane wasn't sealed by some new hire after one of Mooney's many shutdowns and it wasn't done on a Friday Did the Army require gas tanks to be kept full?

Ah, the pedantic bit is set.

I'm with @Vance Harral. Does anyone actually have documentation from the manufacturer or some other authoritative source that tank sealant lasts longer if kept wet? Or, is it just another OWT?

Since we installed my factory rebuilt engine during an annual, we had to measure the compression. We did this cold before we ran it - it had been run in Lycoming's test cell before delivery, of course - and all cylinders were 78/80 or 79/80. At 400 hours it measures between 74/80 and 78/80. There is a lot of variation in the measurements depending on how the rings align and the operator technique. I can get higher readings by a couple of psi than my A&P by jogging the prop back and forth or sometimes spinning it around a few turns and then remeasuring. My A&P can't be bothered and doesn't care. I only do it out of curiosity about how variable it is. Personally, unless you hear a lot of air escaping through the breather (rings) or the exhaust (valve) and/or the compression is really low, I wouldn't worry about it. At the museum, when we got low compression on a cylinder (usually a radial engine, but I don't think that matters) we would just run it up to temp and check it again. Often it was much improved. Skip