The Cessna 120-140 Association Forum

Hello all,

The LH SCOTT fuel indicator gauge sticks when the fuel level gets just under half a tank. I removed the gauge and inspected the float and cam assembly, and I find it kind “grabs” when moving through its range of motion. I tried to tweak it here and there, but to no avail.

Does anyone know a good replacement indicator? Or how to “OH” the Scott units?

Thanks!

A couple of months ago I “rebuilt” mine. I discovered the needle you observe in the cabin is moved by a magnet that rotates through the action of the float and a set of beveled gears. There is no direct connection between the needle and the mechanism inside the fuel tank. Mine also stuck. I removed the mechanism from the tank and discovered the rotating shaft had worn the brass “bearing” that the shaft rides in near the magnet. I suspect the wear comes more from vibration than the rotation of the shaft. In any case I just took a small piece of brass about .065” thick, filed a seat the same radius as the shaft and soldered it in. Works great! The sticking comes from the magnet actually contacting the aluminum plate on which the needle is mounted. I have a picture of the repaired mechanism if you want it. It was an easy and process and cost nothing.
Steve Hawley

Hey Steve, would you mind posting that picture of your gauge you mentioned? Looks like my left tank gauge is a little sticky too and I'm trying to gather as much knowledge as possible before I go off and replace it. Is the binding located on the fuel tank side of the gauge or is it the needle binding against the face of the dial?

Bill,

Check your pm's

Bill, I am very nearly computer illiterate and don’t know how to post pictures. Send me your e mail address and I will send you the pictures. Maybe you could post them to help others with the same problem.
Steve Hawley
hluther205@gmail.com

8224 wrote: ↑Fri Dec 30, 2022 5:24 am Bill, I am very nearly computer illiterate and don’t know how to post pictures.

Expand your horizons! Check out this thread on posting photos.

I had a chance over the weekend to pull down the headliner panel around the left fuel gage and get a look at the gauge mounting flange. Unfortunately, I see the same cracks in the case that others have mentioned come from over-torqueing the mounting screws. It hasn't been leaking, but it seems foolish to attempt a repair on the sticky mechanism when those cracks are present and waiting to sprinkle me with low lead.

The Rochester mechanical gauge advertised on Aircraft Spruce doesn't appear to have any formal FAA approval for installation on the 120/140 despite being heavily implied that it's intended for them. In fact, the engineering drawing for it that Spruce supplies states it's for experimental use only. Is anyone out there with these installed willing to share their story for getting the right paper trail? Is there data to support a field approval?

bill_e wrote: ↑Wed Jan 04, 2023 11:47 amIs there data to support a field approval?

Start with AC 23-27 - "Vintage Parts Substitution". I'm not convinced a field approval will be necessary.

Bill, when I repaired my C-140 fuel gages I did what many do, I tightened one of the screws a tad to much and cracked the aluminum casting. I fabricated a “cover “ plate to slip over the unit with the holes drilled exactly in alignment with the mounting screw holes from some scrap .125” 2024-T3 plate and you have to look hard to see it. Works great but it is better to not need it!
Steve

I highly recomend this:
PL32-40ZMED HYLOMAR MEDIUM GASKET MAKER
Yes it is expensive but a local at the airport recommened it to me when I found both of my fuel guages leaking aroung the gaskets.
You won't have to over torque the screws and it does work.
Ask around, maybe one of the locals at your airport will have some instock and is willing to share.

Rick