Installing Monarch Fuel Caps
One of the best things you can do for your Cardinal, your passengers and
yourself is to do something about those flush fuel caps. Many of us have
sampled substantial water from our fuel, replaced rusty fuel drains and
had various other problems caused by water getting into the tanks. |
You can read more about this problem and the various solutions on several
pages here on the Cardinal Flyers Web Page: Read about your Fuel Cap options, reasons for wanting to change on this page
and read a few comments from someone who
Let's say you're ready to do it, convinced that it's important and ready to
go. If you're like most of us, the next question is 'just how much of a
hassle is this going to be? Is it easy or hard? What do you get when you order a set? What are
the steps? How does it all come together?
You've come to the right place, because we're going to explore all of those
Note that you can load a larger version of each of these images
by clicking on it. (except for the first image of Bill) The image will load in a separate window.
First, a word about the Monarch company. Bill Barton, pictured to the right,
was the mastermind behind these fuel caps. The company has several products,
among them a fuel tank insert that replaces fuel bladders in some applications. |
When I talked to Bill around 1998 he pointed out several differences between
his product and the parts available from Cessna for this purpose. The quality
of construction is the first clue. The fuel inlet has a raised lip, rather than
the the depression of the flush caps or the lowered seam of Cessna's replacement.
The Monarch caps actually rise above the tanks slightly, so it's always an uphill path for
water to get to the tanks. As one side effect, it's said that you can get a bit more fuel into the
tanks with Monarch caps, although no one would recommend that you count on that.
There are several other details worth noting, but this page is about installation,
not a design review of the product. Suffice it to say, Bill put a lot of
thought and effort into making this an excellent design. His many satisfied customers
would tend to agree.
Update: Bill has since passed away and the business has been sold to Hartwig. They have been carrying forward the legacy and making improvements along the way. You can call them at (800) 843-8033.
But if you have them, it's time to install them. Let's start the project!
The parts arrived quickly, well packaged and with everything needed for
installation. Two plates and caps assemblies with keeper chains, the stainless screws
required for installation and the sealant in a clever mixing bottle. |
The package also included all the paperwork required for installation. These
caps are STC'd, so it should be easy for the feds to approve.
No need to ask the feds to accept a 337 from another district and take the chance
of someone taking exception to how it was done elsewhere.
The instructions include a single page for each of several aircraft. If you
are hoping for a step-by-step explanation of how to proceed you will not
find one. This system is designed to be installed by someone who can put
the right steps together. Luckily common sense is enough, and this web page will
help fill in the blanks if this is all new to you.
You won't need much in the way of special tools for this project, but it's
a good time to have an excellent ladder, good lighting, a clean working
environment and plenty of time. The fuel system is not a good place for
There is also a step that should be completed before you start, and that has to do
with the amount of fuel in the tank. Most people will want to drain the
tanks, although I worked out a way to avoid doing so that I'll describe
In either case you'll want to burn the fuel down to a pretty low level.
This is a good time to have a sample tube or dipstick calibrated to your
tanks in order to know just how much fuel is left. Check out
this page if you don't have such a device.
Please avoid the error of one of my neighbors, who went out for a
little flight before a similar project on his 337. He found someone to
fly a little formation with, decided to check out the fall colors just a
few miles further north, and ended up in a corn field with empty tanks. |
If you do decide to drain the tanks, be aware that this is a very
dangerous operation. Running fuel creates electron flow, which creates
sparks, which is bad around running fuel. I've known of a few bad
stories that started with draining fuel.
If you do drain the tanks, just be sure to use a metal
fuel can, a metal funnel and ground everything together and to a
solid earth ground. Don't mess with this one!
OK, we have the fuel empty or way down, a good ladder to work on and
excellent light. Where do we begin?
The first step contains the only significant challenge for the project. The
short version is to simply remove the screws around the old cap. But the
odds of each and every one of those screws wanting to some out is slim.
Start with a large handled phillips screwdriver with an excellent bit of
the right size. Most people will naturally go for a smaller bit than the
screw is designed for. The bit should fully engage the screw. Snapon
makes a bit with serations to help hold the bit in, if you have one
this might be a good time to use it.
You may have to tap the screwdriver to get it fully seated into the
screws. Years of accumulated paint, wax and dirt will tend to make it
a tight fit.
Why all the fuss? Why not just grab a handy driver and give it a go?
One simple reason: once it slips the first time the edges get rounded
and your odds of success go down rapidly, even with the right tools. Do it right
the first time and with luck you've have the chance to wonder what all
the concern was for.
Most likely you'll find at least one screw that resists removal.
In my case one screw on each side initially resisted my efforts. I got
one out by resetting the phillips bit and being VERY careful about staying
straight and fully engaged with maximum weight on the bit.|
But the other required more substantial efforts. As you can see in this
picture, I used
a dremel tool with one of those tiny cutoff disks to cut a notch across
the screw head. It takes two passes to make a wide enough notch, which
gives you the opportunity to give each edge a slight undercut. That will
give the screwdriver a good solid edge to grab.
Keep a thought for where your grindings are going in this process. It's
good to keep that abrasive residue away from the fuel inlet. And remember
the safety glasses... those little disks have a way of grabbing, fracturing and
embedding themselves in anything within their plane of rotation.
Luckily you won't be using the old cap plates, so if you cut a little
extra deep and notch the plate it's not a big deal.
Again pick out a screwdriver with a clean, sharp end, the right size and
tip width for the job. For some reason a longer screwdriver seems to offer
a better engagement and torque. Perhaps it's just an illusion but I tend
to go for longer drivers in tough situations. |
Most likely the screw will give up at this point and back out happily.
If not, there are a few more things you can try:
Alan Valenti suggests using 'Drive Grip', a product containing diamond dust in an oil solution which helps hold the bit to the screw. Others in the past have suggested valve lapping compound, and there are special bits with ridges that help hold on to the screw.|
Worst case there is always the drill and easy-out. Check the nutplates, however, as they are captured and not designed to accept a drill all the way through. Don't drill too deeply or you'll be replacing those nut plates as well, and they are a little hard to get.
Luckily, in most cases this turns out pretty well, with limited hassles.
This is a good time to pull out the power tools. Once the screws are loose
they will spin right out and there are a lot of them. |
Keep in mind that you're working on a fuel tank here, and use battery tools
that do not generate sparks. Of course the old fuel cap is still on, but
don't forget the explosive nature of your project and keep the sparks and
the fuel well separated.
Be sure your driving bit is fully engaged in the screws and have a finger on them
when they pop out. This is a heck of a time to send a big scratch across
the wing with a runaway power screwdriver.
At about this point I was thinking how glad I was that I would not be
re-using the old screws.
Next comes the fun part: lifting the plate. It will be your first glance inside
the tank, and will increase the need for cleanliness. It would be good to
flush away the loose bits before going to this step.
Before you lift the plate, think about where the fuel vapors will be going
once you open it up. Do you have a space heater in use? Hot water heater near
the airplane with an open pilot? Airport bums hanging around with cigarettes
dangling from their lips? |
Remember that fuel vapors are heavier than air, and will flow down a wing
and across the floor to reach whatever ignition source may be near by. Far
too many aircraft and hangars have been lost to inattention to these details,
so give it some thought, ventilate well and keep the fuel covered as much as
In most cases the plates can be lifted by removing the gas cap, inserting
a few fingers, grasping whatever you can get hold of and pulling gently.
If the plate resists removal, I'd start with a broom handle stuck in the
hole to add a little lifting force. Don't try to pry the edge up, you are
much more likely to dimple the wing skins. If you apply a slow, steady force the sealant should release. Just be patient and careful and something will give.
If you are tempted to resort to more dramatic means, say adding a little heat, remember
that you have several gallons of fuel a few inches away and don't do anything
that will create a spark or involves an open flame. Even empty tanks are a
risk, in fact they are somewhat more of a risk. It's just a bad place for
heat all around.
Alan Valenti reports that adding heat worked well for him. He did not say what he
used to supply that heat. If it were me I might consider a heat lamp, something
that would provide energy without a source of ignition.
Richard Markee reports that when he was faced with this issue someone suggested using
a thin knife slipped between to supply a little extra force in just the right spot. He
found that to work well and didn't mention heat being required. Creative, these CFO
It's time to spend a few minutes thinking about how we're going to catch the
little bits of debris that the next few steps will generate. |
Whether you drained the fuel or not, it is not good to dump a lot of
trash down into the tanks. I used a piece of cardboard cut to size and
folded to fit down inside the tanks.
Three lengths of safety wire were used to hold the cardboard in place,
since I had about 10 gallons of fuel remaining in my tanks.
It was enough to simply bend the wire over the edge of the opening, no need
it around anything. That way the wires could be moved out of the way
during the subsequent cleaning steps.
OK! The plate is off, the cardboard is in the tank and ready to catch
falling bits, and we have the chance to step back and see what we have. |
The sealant on my original Cessna plates was very rubbery and surprisingly
thin. But it hung onto the edges of the sealed area very tightly.
I found that I got my best results by running the tip of a box knife around
the edge of the inset area first, releasing the sealant from the corner it was so
tightly bonded to. This is a process to be done with great care, since a
slip here will send a scratch across the wing.
I found that a piece of hardwood was just the right tool for peeling
off the old adhesive. A small block like this, with a relatively sharp
edge, was quite effective in getting under the old adhesive without
scratching or marring the aluminum below. |
I went to some effort to avoid letting chunks of adhesive fall into the
tank, even with the catcher in pace.
I also found that there was a
great temptation to blow the residue out of the way, but blowing
would send fragments to the far reaches of the fuel tank. Don't do that!
The sharp tip of the wooded block was also good for cleaning the
corner of the inset area. I also used the box knife and a small
flat bladed screwdriver to clean out this area.
Step by step.. and there is always another step! I've found scotch-bright
pads to do a great job of putting the final hard polish on aluminum
things like this. No matter how clean they look, after a little elbow grease with
one of these pads they always look better. |
It is particularly important to avoid letting particles from the pad get into
the tank since the are a little harder to filter than the larger chunks
Don't skip the ever present tidy-up steps. A vacuum is the right tool for this
job, since compressed air will send stuff everywhere, inside and outside
The only issue with that is that some vacuums use the air being pulled
through the system for cooling the motor that is pulling the air. As an
electrical device, that motor is often making sparks, not a good thing
when you're slurping up fuel-rich air.
Ideally you'll have a compressed air driven vacuum, many aviation mechanics
do. If not at least use a shop vac that has the motor outside the direct
air flow, and make sure the shop is well ventilated while you do this.
Vacuum well and often, including down inside the tank. Get every little
bit of debris off the cardboard before taking it out of
the tank, since you need to tip it to accomplish that task.
So clean up well, remove the cardboard and prepare to fit the fuel
It's been said that Cessnas were all build by hand, and part way
through this process you will ponder that with a new depth of understanding. |
It is very likely that the openings on the wing will not be large enough
or even enough
to provide a good fit with any insert. In fact they will often be very uneven,
such that a uniform plate that fit into the inset would have huge gaps in some
areas, tight fits in others.
So this is another time for careful, patient work. Set the plate on the
opening and eyeball it. There will be areas of the circumference that
look good, others that don't fit. Using a pencil, mark the areas that
need to be taken down.
I used a belt sander, although any number of tools from a bench grinder
to a mototool could be used. Your goal is smooth transitions, reached
through a well controlled and methodical approach. I would not, for
instance, suggest metal snips or saws; you want to sneak up on the
right shape, not take a big cut and hope you get lucky.
If you do consider a bench grinder you should practice first on a scrap
of similar aluminum. I found a grinder to bend a piece of aluminum if
it was held directly on the wheel. Make sure you know the impact of your
actions before you apply them to the expensive parts.
While you're doing these measurements and careful removal of material,
be sure to be aware of the placement of the holes. As you get close you
might even install three or four bolts on each fit check to be sure that
you're sneaking up on will match the location of the threads.
There is a point in this process where a hand file is the perfect
tool, especially for those odd little edges of the wing skin that
jut out into the inset you're trying to fill. A half-round file will
let you shape the plate to match the hole with fewer trips back to the
Also be aware of the need to have the plate clean before the trial
fit on the wing. Dust of various types could be carried into the
tanks, and you can't have a cardboard catcher during this phase
since the holding wires would be in the way of fitting.
The final step in fitting is the smoothing of the edges. Aluminum,
the material we're working with here, can be easily sanded with a
fine grit sandpaper. Use a file to knock of any burrs, then smooth
the edge by hand with sandpaper, as shown here. |
You will want to practice this before the final fit to get an
idea of how much material will be removed. It's not much, but since
we're doing this job why not shoot for perfect!
Be careful not to mar the top surface of the plate with a slip of
the file or sandpaper. The Monarch people gave us a beautiful top, let's
keep it that way!
I suppose in a perfect world you could protect it with tape, but
a word to the wise should suffice.
It's time to think about painting. You have two choices: you can paint
the plates ahead of time or mask them off after installation and do it
on the airplane. Your choice.|
In my case I did both, but not by choice. I'll let this unfold.. no
reason to get ahead of the story! :-)
Painting is painting, and if you're going to do it you'll need to
know more than I can tell you here. Mask off the parts that don't get
painted, prep the surface with a good cleaning and use a good
There are several things that can go wrong with painting, from fish eyes
to kamikaze bugs. But the most likely problem will be that after all this
excellent work you'll learn that the paint doesn't match like you thought
it did. |
I'd recommend that you paint a little bit of something first and check that
the shade is a good match before proceeding. White is the hardest color to
match, and it changes over time. Enlist the aid of an expert on this, you'll
thank yourself later.
My only other advice, other than doing everything required to do a good
job, is to allow plenty of time for the paint to dry and/or cure. You
might avoid the problem I faced.
The metal work is done, the cleaning phases seem complete, the
paint is drying and
all that's left is the glue and bolt phase. How hard could it be, right? |
Turns out the hard part is figuring out the diabolical little
mixing device. It is not completely obvious. Just consider step one from
the bag that this device arrived in:
"Pull dasher rod toward the neck of cartridge so that the dasher is
at the nozzle end of the cartridge."
This might make sense if you knew what a dasher rod was, which end was the nozzle or if you had a
clue how this all worked. Luckily you're reading this so I can
The plastic bottle contains the glue, while a little pocket of
catalyst is tucked inside the hollow tube. The idea is to take
the solid rod and push it down inside the hollow tube, pushing
the catalyst out into the glue.
So you start by pushing the hollow tube into the bottle, then
pushing the solid tube down the center of the hollow tube. It
might take some force,
it appears that there is a membrane or barrier that needs to
be broken down.
Push the solid rod in and out of the hollow rod until you're
sure the catalyst is out. You probably won't be able to see it
yet, but it's there.
Now remove the solid tube and set it aside.
Inside the plastic bottle is a little mixing wheel. The hollow
tube will thread into that wheel if you push it in and turn it
clockwise. Once the hollow tube has engaged the mixing wheel
you will start to see the effects of the catalyst being stirred in
as you turn the hollow tube.
Turn the tube as you move it up and down until the adhesive is
entirely mixed. They say to mix it for 5 minutes or 50 strokes.
The instructions do not say anything about pot life, but in my
experience I had about an hour to work with the adhesive before
it started getting stiff.
Pull the hollow rod out as far as it will go and unthread it
from the internal mixing wheel. You might have to impede the
rotation of the mixing wheel by squeezing the plastic bottle
from the outside. Remove the hollow rod.
Now you can thread on the little dispenser nozzle that comes
with it and use it to dispense the adhesive without fuss or
That's all there is to it. Not hard at all, right?
One of the challenges of working with adhesives that have a pot life
is that you really need to hurry. I was amazed to download the pictures
from this project and have NOT ONE picture of the beautiful job I did
spreading the adhesive around the inset. |
You'll have to trust me on that, it was a thing of beauty. But by the
time I had it done the glue was starting to stiffen and I got to it,
pictures be hanged!
This is where your careful fitting earlier will pay off. The plate will
fit nicely into it's inset without any tearing of hair or D'oh! sounds,
because you checked it twice before the glue was all mixed up and spread
Just imagine if you had to pull the plate off and fit it now! But no
need, we're set.
Tighten the screws down in a criss-cross pattern, assuring that the
plate sits down evenly and smoothly. As you tighten the screws the
adhesive will squeeze out in a nice bead around the plate. That's your
sign that it sealed properly.. it's a good thing.
You will, however, need to clean up the squeezed out portions before
they set. I found that Stoddard solvent cleaned it up nicely, needing
just a few dozen paper towels to get it looking good.
This is a good time to have the fuel opening masked off, so as to
avoid dumping stuff down into the fuel tanks.
Now for the rest of the story. Since my paint was not yet 2 hours
old, the stoddard solvent nicely remove it as well! So after all my
nice work as documented above, my project was not over.
Masking of the plates on the airplane is really pretty simple. I used
two methods and found one to be superior for a couple of reasons. |
My first idea was to use plastic electricians tape to follow the curve
of the plate. That worked pretty well but had two problem. First, it
tended to lift and return to it's straight form, requiring extra
effort to get it to lay flat.
Second, when I removed it I found that it pulled little flakes of paint
off my wing! Perhaps the paint was not as solid as it should be on that
part of my airplane, and the paint is getting old, but I was not pleased
to see the impact on the surface.
The second method went much better. I used a wide paint masking tape and
just taped over the top, then cut the curves out with a box knife. That was
easier and better in all respects. |
Be sure to use plenty of newspaper and seal the edges. Overspray really
travels across a flat surface like that and a good primer will stick to
anything, including windows and antennas.
Finally we do a good cleaning of the surface, prime and cover coat.
All the same rules apply, but luckily this is a broad, flat surface,
on top, and pretty easy to do. |
A day or two for curing and finally we get to see the results! Naturally
we go back to the first painting advice I gave, which was to check for a
color match before painting.
Since I did not follow that fine advice myself, I learned that the white
paint that used to match my airplane no longer seems to match. So my
project is STILL not over. I'll post a followup once I get it right.
It won't take much to lift the paint back off and do a better job.
If I had it to do over again in the timeframe I had available I would
probably still have gone ahead with this paint. Why? Because it's the
closest paint I had, and I would not want to send the airplane out without
paint on the plates. Weather does bad things to raw aluminum while
you're getting around to getting the right paint. |
So even off color paint is better than no paint. Perhaps this is the
excuse I needed to repaint the entire airplane..??
Then the last step: application of the proper placard for your aircraft. We've all heard the stories of over-zealous Feds who ground any airplane without the proper placards, and although the risk seems low it's still
good to have the right labels. Just wait for the paint to cure out a little before putting them on.
Finally it's over! The total time used was a long afternoon, with several
interruptions from neighbors, visitors and the other normal effects of a
beautiful fall day at the airport.
The caps look great on there, as least as long
as I look from the edge where my paint doesn't show. I'll feel good
about parking outdoors again, and will sample my fuel with a little
In the end it was not a bad project at all. My hands didn't get
cut up, and didn't have to lie on my back or squint at tiny parts
far too close to my eyes. There was no easy way to drop a screw or washer
into an invisible place, and all the parts I needed were there.
If you're looking at doing this project I would not hesitate in the
least. Just be sure you have a good painting plan before you
Keith Peterson, 1999
These pages are a collection of the ideas and impressions of the Cardinal pilots who frequent this site. This information is anecdotal, informal and may not be completely accurate. The Cardinal Flyers are not certified mechanics and do not guarantee the accuracy of the contents of these pages. Please research and confirm anything that is referenced on these pages with the experts appropriate to your situation.
As always, the Cessna maintenance, operations and flight manuals, and the advice of a certified mechanic and flight instructor, should be your primary sources of information regarding safe maintenance and operation of your aircraft.
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