New to me '65 M20C - Annoying radio mounting, water in my fuel, and other questions

[DCarlton]

 Looks like you ** might ** be able to upgrade to a more modern cap / fill neck assembly.  No idea what paper trail would be required.  Worth investigating.  I’m excited about the new caps and necks that come with the bladder kit.  It’s the little things.  

[jeremyc209]

59 minutes ago, DCarlton said:

I may have time to check the parts manual tomorrow too.  Theres a chance it’s the same part.  BTW, before I reconditioned my fuel caps I used to cover them with masking tape prior to any major rainy periods.  

Yeah I grabbed a set of those rubber cap covers off spruce since I didn't know how long it will take me to sort out the repair, they seem to be great quality and were holding on fine in the 38kt gusts out at the airport today when I swung by. The fuselage cover was hanging on for dear life but getting the job done 

[jeremyc209]

41 minutes ago, DCarlton said:

 Looks like you ** might ** be able to upgrade to a more modern cap / fill neck assembly.  No idea what paper trail would be required.  Worth investigating.  I’m excited about the new caps and necks that come with the bladder kit.  It’s the little things.  

Yeah it seems like most options aside from serviceable originals are very spendy. Stainless would be great but not for 800/wing in parts alone right now if I could even get them.

I wonder if I have something similar to that poster going on though, my left tank is pretty decent while the right side is pretty bad. I need to take a closer look. 

[AJ88V]

10 hours ago, DCarlton said:

We just removed the fuel cap flanges on my ‘67F to install bladders.  They come with new fuel caps.   If they are the same part, you can have them for the cost of shipping.  If interested I’ll make some pics.  I’ll need to make certain we won’t need the parts.  

That's an amazingly generous offer @DCarlton.  Good on you!!!

[DCarlton]

On 3/12/2025 at 9:52 PM, jeremyc209 said:

Yes! That sounds great, I'll look up the catalog for your F to compare part numbers and PM you. Thank you!

Two fuel cap adapter plates are on the way priority mail.  Sorry for the delay.  I had to check one more time to make absolutely sure we didn't need any of the parts for my bladder installation.  If you don't need them or can't use them, please pass them along to someone who can.  Good luck.

[jeremyc209]

Awesome! I bought a set of these cap covers to use in the meantime since we tend to have a lot of weather come through this time of year and they've definitely got a lot of good use already. (pic from spruce)

[jeremyc209]

Got the wingtips sorted. Some decent matching paint came with the plane.

Are these same switches available from spruce or elsewhere? The fuel pump switch is pretty "loose" in particular but a couple of them are getting there. 

My beacon occasionally doesn't work as well but I haven't confirmed if it's the switch. Wouldn't surprise me though. It's a strobe, not sure if they're prone to other intermittent issues. (It works without the other strobes on)

I secured a small hangar at my home airport though, one of the few private hangars came up and I asked around at the right time. The public hangars are probably a 5 year wait so I'm definitely happy!

[jeremyc209]

Anyone know what this is? Under the copilot side of the panel by right knee. Two red capped ports and another with clear PVC attached but it's just open under the panel, it doesn't attach to anything else. Small connector with a few wires and a "14v" sticker.

[Andy95W]

That looks like an avionics cooling fan.

[jeremyc209]

10 hours ago, Andy95W said:

That looks like an avionics cooling fan.

That makes sense, is the tube supposed to just dump air a little higher than the box but behind the radios? Seems like a lot of trouble to move air a foot or so in the same air space. 

[Andy95W]

Older avionics had/have a tube on the back of the rack that the hose would fit on.  Modern avionics tend to not need additional air cooling unless they’re being operated in significant heat like the desert.

It’s possible that the avionics shop that did some of the installations didn’t bother to connect the hose to any of the radios but just capped off most of the ports and pointed the one remaining to the backs of the whole radio stack.  Easier than removing a functioning fan that could still do some good.

[jeremyc209]

Finally getting into the Positive Control + Accu-Trak system

The previous owner gave up on it years ago, and I want to get it working before I install a GPS and better CDI. I’ve made some good progress, but I’m pretty sure the tail gyro is dead, and Accu-Trak seems way too aggressive.

---

What I’ve done so far:

• Reinstalled both aileron servos — surprisingly easy with a short 4" ratchet and a cheap borescope for visibility. A square-handled rubber ratchet helped keep orientation by feel.

• Vacuum tested the ailerons from the tail

• Replaced all vacuum lines in the tail.

• Reconnected the pilot valve to the remote gyro (the hose had been knocked off under the panel).

• Vacuum pump was replaced (unrelated failure); vacuum gauge now shows ~5.25 in Hg in flight. IIRC it was reading a little lower before I fixed the pilot valve -> gyro connection.

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PC System — possibly dead gyro?

• No spin-down sound from the tail gyro after shutdown (checked with my ear right at the tail).

• Controls feel stiff and override works fine.

• Yoke doesn’t react on the ground or roll level in flight when released.

• It does hold heading pretty well now when trimmed, so vacuum is definitely reaching the system.

Thinking I may pull the gyro to clean and re-lube the bearings, I saw a thread where another member did the same. Also considering getting a differential vacuum gauge to dial in restrictor #3 properly.

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Accu-Trak — acting way too aggressive

• Currently hooked to a KI-209 CDI.

• When tracking is enabled, it banks hard (well past standard rate), then overshoots and reverses hard the other way.

• Needle deflection doesn’t seem to affect how hard it banks.

• Hi/Lo switch doesn’t seem to change behavior.

• L/R turn knob works, but not sure what’s considered “normal.”

I’m planning to check the internal gain trim, confirm the Hi/Lo switch wiring, and possibly have the shop dial vacuum back slightly if it was cranked up when the pilot valve was disconnected.

---

Before I call Kevin, just wondering if there’s anything else worth checking.

[65MooneyPilot]

Way back when I had  the gyro overhauled. I have no idea what they actually did to it. When you taxi to the runway it should definitely move the yoke while you are taxiing. I check mine just as you would for an IFR flight checking the gyro. I just have the PC system, no accu-track. 

[Matthew P]

On 3/4/2025 at 1:39 AM, jeremyc209 said:

Found the stainless fuel filler necks on Lasar, I think, $740 each  and out of stock. Will make some calls. 

Anyone have a good preflown set? Is the stainless replacement pretty much the only route? 

call don maxwell

 

[jeremyc209]

1 hour ago, Matthew P said:

call don maxwell

 

Got those sorted, thank you.

[jeremyc209]

Ok, this is how the PC turn coordinator looked before I replaced all the vac lines. See the problem?

I just put all new lines on and fixed up the connections in the tail but I missed a fairly important detail.

 

[47U]

45 minutes ago, jeremyc209 said:

See the problem?

I’ll be the guinea pig and take a shot.  

I’d say the black vacuum hoses to the filters are looking pretty tired… but I don’t have an autopilot in my ‘63/C and have never seen the installation in the tail.  Is that it, or something else?

[jeremyc209]

12 minutes ago, 47U said:

I’ll be the guinea pig and take a shot.  

I’d say the black vacuum hoses to the filters are looking pretty tired… but I don’t have an autopilot in my ‘63/C and have never seen the installation in the tail.  Is that it, or something else?

Yeah they were definitely shot but the problem was present before and after replacing them. Hard to spot the issue without knowing the system I think.

[65MooneyPilot]

Looks like the vacuum line to the gyro is not hooked up. Wonder if they disconnected it because the gyro was making noise or not spinning? I guess you need to hook it up and find out. That explains it not working. 

[jeremyc209]

1 hour ago, 65MooneyPilot said:

Looks like the vacuum line to the gyro is not hooked up. Wonder if they disconnected it because the gyro was making noise or not spinning? I guess you need to hook it up and find out. That explains it not working. 

All the lines are connected, those red capped ports are test ports. I did pull the TC and check the gyro before realizing the problem, it spins fine.

Side note for anyone wanting to check if the gyro spins:, an easy way is to run a little compressed air into the inlet side, it'll spin it right up. I just hit it with some nearly empty canned air since that's what I had on hand and it spun for a couple minutes.

[jeremyc209]

Here's a hint from one of the diagrams in the service & maintenance manual:

[47U]

16 minutes ago, jeremyc209 said:

Here's a hint

I’m guessing it’s 180 degrees out of whack.  Diagram shows the nipple on the top, picture shows the nipple on the bottom.  So, that filter is hooked up to the wrong port.

[jeremyc209]

16 minutes ago, 47U said:

I’m guessing it’s 180 degrees out of whack.  Diagram shows the nipple on the top, picture shows the nipple on the bottom.  So, that filter is hooked up to the wrong port.

Yep!

I feel dumb for not realizing. It was mounted upside down by the last person who worked on it. I got the left/right lines on the correct ports when replacing all the lines but just hooked up the vac and inlet filter to the same ports it was on before, which were reversed.

Haven't had a chance to test it yet but I'm guessing that solves my issue, hopefully today.

[Flyler]

I think @takair is knowledgeable about these systems too, it you haven't already fixed it.

Really glad to see you got a hangar and are getting the plane fixed up! Great pictures too.

[jeremyc209]

It works! A little inconsistent, I'm not sure what a normal functioning PC system is like though.

Sometimes it will return to level but overshoot, then come back. At least once or twice in the short time I was up today, it would overshoot but not come back. Maybe something sticking in the gyro? The roll trim on the yoke is not super responsive, is it supposed to be a fairly faint trim adjustment?

The Accutrak still gets off course a little then starts overcorrecting hard. I haven't tried making any adjustments to it yet since the PC system still isn't 100%.