The Engine Show - 2008/08

“Warning: For the break-in period we do
not recommend using fuel that contains only
synthetic lubricants. Synthetic lubricants have
a much lower flash point than Castor Oil
lubricants. Flash point is the point at which the
lubricant begins to actually burn and lose its
lubricating qualities.
“Using fuel containing a blend of Castor
Oil and synthetic lubricants results in an
engine that runs cooler and lasts longer. One
lean run using a fuel containing only synthetic
lubricants can cause engine failure. Using fuel
with a Castor Oil and synthetic blend of
lubricants greatly reduces this chance.”
Amen to that!
When I installed the glow plug in that
Magnum 180, I used a trick I came up with
awhile ago for installing glow plugs into
deep-well cylinder heads. A pin vise gripping
the center terminal of the plug allows it to be
accurately positioned and screwed lightly into
place. After that, a regular socket-type wrench
of some sort completes the tightening job.
For many years I’ve been using a portable
test bench for breaking in model engines. It
can permit as many as eight power plants to
be run simultaneously, and it’s easy to
disassemble for transportation.
At flying sites, modelers have seen me set
up this multiple-engine test stand. They come
around to take measurements and shoot
photos so they can go home and build similar
units for themselves.
Magnum XL 180 RFS engine
Also included in this column:
• Portable test stand
• A handy hint for installing
glow plugs in deep wells
• Source of 1/2A engine fuel
August 2008 97
The Engine Shop Joe Wagner | [email protected]
MAGNUM’S BIG XL 180 RFS four-stroker
is a ringed-piston design and a mighty potent
engine. Weighing 39 ounces, it’s extremely
well made and spins a 16 x 8 propeller from
1,800 to 10,000 rpm after being fully broken
in.
I have to admit that the XL 180 gave me
some difficulties at first. Although I followed
the factory-provided instructions to the letter,
this engine’s extremely high compression
when new made it impossible for my
TorqMaster 90 starter to turn it over.
In correspondence with other modelers, I
learned that’s a common issue with this
engine. They advised adding an extra head
gasket. But I wanted to test the engine exactly
as it was supplied to me.
Hand-starting attempts on the Magnum
180 produced mostly hard raps on my
knuckles (through the heavy leather glove I
wear when hand-starting any engine
exceeding .15 cu. in. displacement). For
safety’s sake, I had to make a “chicken stick”
from a length of 1-inch birch dowel wrapped
with several layers of vinyl electrician’s tape.
Once in awhile the big Magnum’s kickback
would even knock that out of my hands.
The main problem I had was getting a
proper prime. In its upright position, most of
the fuel drawn from the tank when choking
the Magnum would drain out as soon as I
removed my finger. The short inlet passage to
the carburetor minimized the momentum of
the incoming air. That made it quite difficult
to get the right amount of prime into the
engine for starting without backfiring.
Since I’d been told that this particular
Magnum 180 would be used for powering a
big RC Chipmunk, I knew it would be run
inverted. I revised my test mounting to an
inverted installation. Doing that solved most
of my start-up problems. I could drip two
drops of fuel down the intake and then hook
up the glow plug. Then one or two hard flips
with my big chicken stick would get the
Magnum perking nicely.
I used the recommended hot plug that
came with the engine and carefully made the
fuel blend the instructions specified for breakin:
9% nitromethane and 20% lube content—
half synthetic and half castor. The instructions
read:
“Use of fuel containing more than the
recommended percentage of nitromethane, or
only synthetic lubricants, will cause the
engine to run too hot and result in excessive
wear and engine failure in a very short period
of time.”
I believe that! The Magnum manufacturers
want their customers to be successful with
their engines, and they go into further detail
about fuel.
Left: Ringed-piston Magnum XL 180 RFS
looks and performs great. It was hard to
start when new, but was friendlier after
running through two quarts of fuel. All
photos by Allison Leger.
Above: Installing a
glow plug in a “deep
well” (such as on the
Magnum 180) is easy
with the aid of a pin
vise, as shown.
Left: The Magnum 180 was
to be used in a Giant Scale
Chipmunk. Test-running it
in this inverted setup
showed no problems—and
starting it became even
easier. The top is a hard-pine board measuring
111/2 x 27 x 11/2 inches. It’s supported by four
splayed-out legs made from a single 8-foot,
long, hard fir or spruce 2 x 4. I used those
instead of commercial legs—the kind that
screw into metal baseplates at the top—
because I tried those in earlier versions of this
test stand, and they didn’t hold up. Vibration
from the engines, plus the various lateral loads
from “handling,” caused failure within a week
or so.
The key to this test stand’s strength and
portability is the leg design. I sawed the 2 x 4
in half, and then cut each half along its
diagonal. That produced four leg blanks.
Next, I carefully sawed the wide end of each
leg blank to a 15° angle. This surface needs to
be straight and smooth, because it’s the top of
the leg and it supports everything.
The legs on my test bench are 32 inches
long overall. I’m 5 feet, 6 inches tall, and that
leg length puts the engine test mounts at a
convenient height for my use. If you’re taller,
use longer legs. The pointed ends of the legs
are cut off to provide the desired leg length.
Parallel with the top, and 3 inches below
it, I cut a 1-inch-deep notch on the acuteangled
side of each leg. That’s for the T-nuts
the 3/8 x 4-inch hex bolts thread into to hold
the legs and top together.
Those bolts—and washers—fit into
counterbored holes in the corners of my teststand
top. That prevents protruding bolt heads.
But if you have no way of counterboring, you
can use longer bolts and put up with the
protrusions.
I attached several different test mounts
around the perimeter of the top of my engine
test bench. Some are homemade; others are
modified commercial types. I’ve never seen an
engine test mount that would truly accept any
size engine.
The slide-out drawer in my unit is 11 inches
long, 13 inches wide, and 4 inches deep. I
made that from scratch, but you may have a
similar-size drawer from an old end table or
some such item that can be adapted.
Driven partway into the center of my testbench
top is a big screw. This is an anchor
point for a heavy nylon cord that’s 5 or 6 feet
long, and its other end is tied to a tent peg.
Driven firmly into the ground at a flying site,
the peg and its cord prevent the stand from
being pulled over by the thrust that a big
engine develops.
Two readers have brought to my attention that
1/2A glow fuel is still available from Sig, via
Tower Hobbies. Sig’s 25% Nitro Champion
Fuel’s 20% total oil content is half castor and
half Klotz synthetic.
For running in Cox engines (and other 1/2As
with ball-and-socket connections between their
pistons and rods, such as Baby Spitfires and
Holland Hornets), it’s a good safety measure to
add 2 more fluid ounces of castor oil to each
quart of Sig’s 25% nitro-blend glow fuel.
That’s because the piston-to-rod ball-andsocket
connection not only bears the full power
load that the piston transfers to the crankshaft
at every stroke, but it’s also the toughest area in
the engine to lubricate.
Think about it. Oil gets into that bearing
area purely by accident. That oil needs to be of
the highest film strength and adhesion—and
only castor will do. MA
Sources:
Magnum engines
(800) 854-8471
www.hobbypeople.net
Tower Hobbies
(800) 637-6050
www.towerhobbies.com
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