New cylinder and more


Some updates on the unkind month of January! For a recap, a triple dose of unluck hit N194SP. A bad coil in the left magneto left it stranded in Watsonville. A tumbling AI needed an overhaul. And a bad #1 cylinder wouldn’t hold compression. None of these alone should cause an immediate safety concern for the aircraft, but they definitely aren’t situations that can be allowed for further flight. This is why the plane has two magnetos. And why we train partial panel. And, of course, even with a cylinder only holding 20 psi, it was still smoothly making full power.

Still, it had to all be fixed. As I mentioned in the last post, a new $1500 Slick magento was popped onto the plane in Watsonville with four and half hours labor. That got it back home. It turned out the other magneto was due for its 500-hour inspection. Three hours of labor and $60 in parts made sure that the right mag is now behaving just as well as the new left.

The AI was a simple swap. $1000 for the overhauled unit and an hour to swap it out. I’ve flown the plane since the overhaul, and it’s now nice and stable.

The cylinder was more involved. First, it was an $1100 part, though it was fortunately available off the shelf. Overnight shipping and ten hours of labor later, and a new cylinder graced the Lycoming engine. Total bill: $2325. Unfortunately, it wasn’t done yet. The cylinder needed to be broken in for ten hours of tach time before it could be flown as a rental. A couple other ferry pilots got some time, but I did most of the break-in time, flying all weekend. I got several new airports in my logbook, which was great. Not so great is that I had to do it solo. I always have more fun when I can share!

Other items that were done during the 100 hour:

  • New ELT battery was installed.
  • New right main tire.
  • Leaking fuel strainer valve was replaced
  • New ground strap on the left elevator
  • Fixed the bad screw in the cowl.


New cylinder and more

Some downtime for the engine

Sometimes in plane ownership, luck is not with you. The engine on N194SP decided it needed to get some heavy maintenance at its half-life. Nothing too terrible, but January has had some downtime for the aircraft.

First, the left magneto gave up the ghost. The coil failed in the magneto during a flight to Watsonville. Of course, the right magneto continued humming along nicely, so there was no threat to the safety of the flight, but it doesn’t leave the plane in a condition to be flown home. WVFC’s chief mechanic flew to KWVI to swap out the magneto. Four hours of labor and a $1500 part, and the plane was flying again.

The good times lasted another couple weeks. The plane went in for a 100-hour inspection, and they found that one of cylinders had lost compression. It was still producing power, but something is dreadfully wrong with it. An overhauled cylinder is being put on, and we’ll hopefully be flying in a week or two!

Some downtime for the engine

Autopilot issues

So, you may have noticed there have been some issues with the autopilot lately. Turns out, there are probably two things causing that. The roll servo was intermittent in one direction. That would mean the plane would roll one way, but be unable to roll back the other. The roll servo was overhauled to the tune of $2,250. As a result, Roll and Heading modes should work perfect again!

Nav mode, however, is more troublesome. While in the shop with Aerial Avionics, we noticed that the reported OBS to the KLN 94 would get stuck at 47 degrees or 227 degrees, depending on the TO/FROM flag. But only intermittently! The culprits could be the CDI (around $1200 to overhaul), the GPS/NAV switch ($1200 for a button!), or just dirty or loose connections. After clean-up, it does not appear to be having problems anymore, but please keep watching it and let me or WVFC know if you see issues with the AP in Nav mode.

While there, we got ready to fix two other issues. The clock has been having issues. I ordered a new one for $600, so that should get replaced very soon. Also, the display on COM1 can be unreadable when cold. This is a known issue with the EL displays on KX155A. An LED replacement display has been swapped in and we’re just waiting to get it installed. Should be about $1500.

Lastly, there have been a couple reports of the HI becoming intermittent. Please keep watching it. I need to either overhaul it, if it’s bad, at $1500, or replace it with a Garmin G5 for about $4000.

Happy flying, everyone!

Autopilot issues

Made some KLN 94 tweaks

Hello all. I had a chance, as a result of the issues the KLN 94 GPS has been having with reading a correct OBS from the CDI to tweak some of the configuration of the KLN.

  • Hopefully fixed the issue with the CDI. Could you all monitor it to see if it’s really fixed? The issue was that the CDI’s OBS was being read as 45 degrees off by the KLN. It’s been adjusted, and let’s watch it to ensure it stays accurate.
  • QuickTune! If you search for a frequency in the KLN, you can now push it to COM 2 or NAV 2 by just moving the cursor to the frequency and pressing ENT. I can actually configure it work with COM 1, COM 2, or both. I chose to only go to COM 2 and NAV 2. This skips the step of selecting the radio to send the frequency to and also allows you to put the NAV frequency into a CDI that isn’t being used already by the GPS.
  • The connection to the KMD 550 MFD was made more robust. More information should now show up on the large moving map.
  • The configuration for the KAP 140 autopilot’s interface with the KLN 94 was improved. The autopilot should behave better now.

I hope you all enjoy the improvements. Let me know if something goes wrong or if the stuff doesn’t work like you’d want it to.

Made some KLN 94 tweaks

Flying again, but no sender type change

Well, N194SP is flying again. It’s been way too long that the plane wasn’t flying, and for that, I apologize. This has been a painful lesson in how things work in the aviation industry. I now know what I should have done in hindsight, but each decision sure made sense when I was making them.

First, you’ll see that the fuel gauge in the plane hasn’t changed as it was supposed to. That’s because it’s flying on the Rochester part. Granted, it’s a brand new part, sourced from Air Power for $650. The CiES units and all the parts and work that go along with putting them in were going to take another month. I couldn’t afford that. So, the stock Cessna part went back in. Of course, that’s what I should have done from the first, but live and learn.

Second, I still ordered the CiES units. They’ll arrive in about a week. I don’t know how I’m going to show the level. There are three options: convert the signal to resistance and show it on the stock gauge, buy the Aerospace Logic fuel gauge for almost $1000, or get an EI CGR-30P engine monitor for $3500 (plus lots of labor). If I do anything with them, it will probably be right around annual.

So, question to my flyers: What’s an engine monitor worth to you? I’d need to add a few dollars an hour to account for the cost of the system. Is it worth that to you?

Flying again, but no sender type change

Fuel sender saga continues

I was going to wait until the issues with the fuel sender were finished to write an entry on it, but it’s going on for a very long time and people are wondering what’s up with my plane. Here’s the current story:

The right-hand fuel sender, a unit made by Rochester for Cessna, is notoriously poorly made. It’s a pretty standard unit, quite similar to one that you’d find in your car. It has a float that operates a potentiometer (variable resistor). The range is 5 ohms to 90 ohms with higher being less fuel. The pot in this design of the Rochester part is what’s known as a film pot: there’s a carbon film deposited on plastic, with a wiper that sweeps across it. The float operates the wiper. The traditional method of using windings of wire is much more durable, but also much more expensive and heavier. The quality of that carbon film is terrible and quickly wears away. This is what happened earlier, but Instrument Rebuild was able to clean it up and make it work again.


It didn’t last. The rebuilt unit started failing at about six months time in service. It turned out that rebuilding the unit was a false economy for a rental. It may have made sense for a personally owned aircraft that didn’t fly much, but on a rental it turned out to be wasted money. It was $400 for the rebuild, and 2-4 hours of labor for each swap. When the unit failed again, I sent it to Instrument Rebuild, hoping they’d honor the warranty.

They attempted to. Unfortunately, the owner of Instrument Rebuild, Paul Malkasian, has passed away. His son, Bill, is minding the shop. Bill attempted to revive the unit, but the pot is too far gone. He’s currently attempting to get a replacement pot from Rochester, but he’s getting no response from them. He’s attempting to honor it, but it’s not working.

Meanwhile, my plane is sitting. And I am giving up on the Rochester part.

Instead, I’m replacing it with a CiES digital fuel sender. The CiES unit is half the cost of the Cessna unit ($400 vs. $800). It not a pot: it’s a magnetic sensor attached to the float. It’s sealed and enclosed. It should last longer than the plane does. It should be far more accurate than the old Cessna parts. And it’s STC’ed for 172S.


The downside is that the plane will be in repair for a bit longer. The fuel gauge is not compatible with the digital units, so a digital fuel gauge is on order. That’s $675. Of course, I also need to replace both fuel senders, so the cost is still $800 for the senders, not just the $400 to fix one. And the kicker is that both the new gauge and the new senders are active. That means they need to be supplied with power. For the new gauge, that’s not a big deal, as it’s in the panel where power is readily available. For the new senders, it’s more of a problem, as a new wire needs to be run to each tank to supply the sender with power.


All-in-all, it should be about 8 hours labor to get the new system in, or about $2000 total. Add to that the lost revenue from having the plane down for so long, and this has been a very expensive and hugely annoying failure. Once the CiES unit is in, though, that should be the last of these issues!

I’ll post up again when this is all resolved with the final numbers!

Fuel sender saga continues

Annual at WVFC

Yeah, I’m a bit late with this…this happened in November. It took a while to get all the information compiled, as I was new to West Valley.

In November, the plane had an annual at West Valley Flying Club’s maintenance department ahead of being placed on the line at WVFC. It was a relatively easy annual, and was done easily on time. In fact, the plane got its first renter in November, ahead of the stated on-line time of December!

As a summary, the annual inspection was $1260 for the inspection itself, plus $180 for the AD research. It was found the that Slick magnetos were due for their 500-hour inspection, which ran $360. This would be the first time the magnetos were inspected since the engine overhaul, and they needed points and new plugs. $155 put in new points, $150 put in new plugs. Of course, oil was changed during the annual, which ran $160.

The annual also found some issues at the very bottom: brakes were worn and one tire was flatspotted. $100 for a new tire and $180 to have it installed fixed one problem. $55 for brake linings and $180 for installation fixed the other problem. Also, in the process of putting it on the line, four spare quarts of oil were put in the club box in the plane for $35. All told, the process cost $2,900.

The plane spent much of November not flying due to the club move. As a result, flying hours from WVFC were only a single flight of 1.1 hours. November was definitely a losing month, but I expected that.

Annual at WVFC