While Eagle series engines are powerful, and generally well made, they may also exhibit some frustrating running qualities that prevent many users from enjoying their full potential. By applying the following modifications
you can, in many cases, significantly improve the running and
handling qualities of your Fox Eagle .60 engine.
Why are modifications
Our experience with Fox
Eagle series engines over the years has revealed two primary
components which may cause running or reliability problems. These are: the head button, and the EZ series carburetor (on those engines so
equipped). We'll summarize each of these briefly:
Problem #1: Head Button:
When the Eagle II was
introduced, Duke Fox was determined to try the get the best performance
from FAI (no-nitro) fuel. This resulted in a rather high compression
ratio. While he did manage to get quite a bit of power from FAI
type fuel, in our opinion, the running and handling qualities
of the engines suffered. Many engines tended to run hot, were
finicky to adjust, and would often "flameout" during
throttle transitions. This was particularly true when the nitro
content exceeded 5%. In the Eagle series, II through the present
version IV, numerous head button variations were tried over the
years in an attempt to reach a suitable compromise, however,
we feel this was never fully achieved. While the current head
button is a big improvement over earlier versions, some problems still remain. We'll show you how to solve these.
Problem #2: EZ Series Carburetor:
While the EZ series carburetor appears to be just a simple air-bleed type, internally it is actually
more complex than that. The throttle barrel also contains a metering
system to control the mixture through the mid-range as well.
It is the metering system that we have found to be a problem.
Because it is fixed, (non-adjustable) metering problems can occur
in some cases. In particular, we have found the upper-midrange
(just below full throttle) is often too lean. The engine may
run fine at full throttle, and idle well, but as the throttle
is reduced slightly from full, the engine may run too lean and sag, surge
or even quit. Numerous, unexplained deadsticks may occur. When
the aircraft is retrieved the pilot often finds the engine to
be hot even though the high-speed mixture seemed fine on the
ground. The engine is started again, checks out ok, but the same
thing happens on the next flight, and the next. When this is combined with the head button problem, a very unfriendly
engine can result. The carburetor problem can be fixed, however,
and we'll show you how to do it.
A Fix for the Head Button Problem:
The basic fix involves installing the very
latest head button (from the current Eagle .60 IV) and, possibly,
up to two .010" head shims. The current head button part
number is #60125. The shims, which are just the head gasket from
the old Eagle I series, have no listed part number but are still
available from Fox. Note: If you purchased your Eagle .60 within
the last few years, it likely has the current button, so you
will only need the shims. First try the new button without any
shims. If you still experience flameouts or overheating then
add the shims as shown in the following diagram. The number of
shims required depends upon such things as nitro content, and
the elevation of the flying site. Near sea level, using typical
10% sport fuel, both shims are generally required. At higher
elevations the engine may run fine with only one, or even none.
Generally, more nitro = more shims. Don't use more than two shims,
however, as the power may drop significantly, and/or you may
again experience running problems.
Installing Head Button
Shim Side Effects
The number of shims required depends upon such things as head
button version, propeller size and nitro content. The altitude
of the flying site also plays a part. The closer you are to sea
level, the more head shims are required. Engines operated at
higher altitude sites may run acceptably with no shims at all.
We recommend adding no more than two .01" shims. If too
many shims are added, power may be significantly reduced, and/or
the engine may not be able to attain a proper two-stroke setting.
As you try to lean the needle it may just quit abruptly. Adding
shims also has the undesirable effect of moving the glow plug
higher up in the combustion chamber and, if carried too far,
can again bring about unexpected "flame-outs".
A Custom Head Button
While the basic
fix is generally acceptable, if you have the capability to do
a bit of simple machining, the "current" head button
can be improved further. By lowering the position of the glow
plug by .030" and adding a 5 degree angle, and a slight
radius, to the squish band, you can achieve a super-smooth running
engine. The diagram below shows the details. The squish band
angle is not ultra-critical, and the radius can be easily achieved
by wrapping some #400 sandpaper around a small dowel, and working
the inner edge while spinning it up in a lathe. Don't get too
carried away, just round off the sharp edge a bit. Again, not
really critical. The shims mentioned above may or may not be
still be required after the button modification. Start without
them and add one or both as required.
If you would like to try a modified
head button, but don't have the ability to do this yourself, we have a recommended source for custom machine work.
Head Button Modification
Note: The button modification does
not apply to the .74. The .74 button is quite different in design
and requires a custom made button.
Head Clamp Modification:
little modification we like to do involves machining the surface
of the head clamp where it contacts the head button. The head
clamp casting tends to be quite rough and/or porous which reduces
the surface area contacting the head button. We have seen quite
a number of engines with a layer of baked on castor in between
the top of the head button and the head clamp. Machining this
surface allows full contact to further aid cooling. Although
only a very small amount of material will be removed, we also
recommend removing an equal amount from the bottom of the head
clamp. The head clamp comes very close to the cylinder casting
and this will ensure that it does not contact the cylinder before
the head button is properly secured.
A Fix for the EZ Carburetor:
An overly lean upper-midrange may be exhibited
by some EZ series carburetors, particularly on larger Fox engines.
Here is one way to help determine if you have this problem: Adjust
the needle valve for proper full throttle operation. Adjust for
maximum speed, then back off (richen) a bit so the engine slows
down a few hundred rpm. When the nose of the model is held up,
the engine should not sag. Now, with a friend holding the nose
up, slowly reduce the throttle from full. If there is
a range in which the engine surges, sags, or quits, you have
the carb. problem. Note: Do not hold the nose up for extended
periods as this will increase the operating temperature and could
result in a false indication. If the problem is present, it can
be cured with a modification to the throttle barrel. Remove the
barrel, then use a small round "needle" file to elongate
the fuel jet hole as shown in the picture below. The modified
fuel jet provides a more gradual transition to the thin metering
slot, richening the upper mid-range. File a little at a time
then reassemble the carb. and test run. Continue to elongate
until the problem is gone. Be sure to clean the barrel thoroughly
before re-installing! If you go a little too far, the engine
will just be a bit rich in the upper midrange, which is actually
desirable anyway. The picture illustrates the typical amount
the fuel jet hole must be modified on the .60 size engine.
EZ Carb. Throttle Barrel Modification
If you would prefer not to play around with modifications, another option would be to install a Perry carburetor.
Some recent problems:
There are new problems showing up in more recent engines. These are related to a combination of the EZ carburetor and a modification to the crankcase. The crankcase has been modified internally to include a thin slot that runs between the carb. intake and front bearing. The intent was for the intake vacuum to prevent fuel from leaking past the front bearing while the engine is running. Unfortunately, in some cases, too much air is also drawn in through the slot upsetting the mixture. (This is basically an air leak!). The air-bleed EZ series carburetor may not have the adjustment range to compensate for this, resulting in the inability to achieve a proper mixture adjustment. Often the engine will run poorly in the low to mid-throttle range although some engines suck in enough air that they run poorly over the entire throttle range. The engine need not be disassembled to check for the presence of the slot, just remove the carburetor and the end of the slot is visible as shown in this photo . We have been filling the slot with JB weld to fix the air leak problem, but this must be done carefully so that the operation of the crankshaft is not impeded. The engine must be disassembled, then remove the front bearing and clean the crankcase thoroughly with solvent. Carefully fill the slot (using a toothpick, etc.) trying not to get too much excess. Allow the JB weld to set for a while, but not fully cure, then insert the crankshaft. The front edge of the crankshaft will neatly scrape away the excess JB weld for a perfect fit. Allow the JB weld to cure fully before installing the front bearing and re-assembling the engine.
An Important Final Note:
It is important that your engine still
be in good condition before employing these modifications. The
tendency to run hot can result in an engine that is "fried" in very few flights as the frustrated pilot tries over and over
again to get a complete flight without a flameout. Your Eagle
.60 should have strong, snappy, compression when you flip it
over. If this is no longer the case, you will likely need a rebuild
first. The modified head button, or shims, cannot be expected
to cure a worn or damaged engine.
If you have questions related to
your Eagle .60 you can use our contact form