The Engine Shop - 2008/02

New O.S. Alpha .56 four-stroke engine
Also included in this column:
• 1/2A fuel sources
• Wooden mufflers and
aluminum extensions
• An easy way to degunk sticky
shaft bearings
February 2008 83
The Engine Shop Joe Wagner | [email protected]
Above: An improved carburetor,
compact muffler, and short pushrod
tubes distinguish the .56 Alpha from
previous O.S. four-strokers. The needlevalve
extension is necessary.
Right: A side-by-side comparison of an
earlier O.S. FS (L) with the Alpha shows
subtle yet all-important external changes.
Below: Yes, the muffler on this Fox .36X
is made from wood. This test showed that
usable homemade mufflers don’t require
a machine shop.
O.S. NEVER seems to run out of
improvements to its already superb line of
engines. The new four-stroke .56
demonstrates that nicely. O.S. calls that
engine “Alpha” because it’s the first in a
series of single-cylinder, overhead-valve fourstrokers.
Externally you can see the Alpha design
approach in a new, more compact muffler,
shortened pushrod tubes, a different
carburetor assembly, and the absence of a
crankcase breather. The latter is because of a
novel internal system for lubricating the shaft,
ball bearings, gears, and cam/followers
assembly.
For their lower-end lubrication, earlier
four-strokers depend on the small amount of
oil that the combustion-chamber pressure
forces through the tiny clearance gap between
the piston and cylinder sleeve. The Alpha .56
uses a much better system.
There’s a small hole through the head
alongside the intake valve. It allows
02sig3.QXD 12/20/07 12:20 PM Page 8384 MODEL AVIATION
It took only an hour to complete a barstock aluminum adapter for adding a Fly Quiet
muffler to this old O.S. .15 engine.
Glow fuel for 1/2A engines can be hard to
find, but Tower POWER 30%-nitro
helicopter fuel with added castor works as
well as Cox’s Racing Fuel did.
The smallest RC glow engine ever marketed came complete with
a fuel tank—and a muffler! The G-Mark .031 has long been extinct.
crankcase vacuum on the intake stroke to draw a minute amount of
fuel-and-oil mixture downward and into the region surrounding the
shaft and cam assembly.
From there a hole in the shaft and a cross-port between the bearings
delivers oil to those—but not a lot. The Alpha .56 doesn’t spit oil from
behind the propeller driver. Nevertheless, enough is forced into the
front bearing to provide the lubrication it needs for long service life.
There are two major differences between the Alpha’s new
carburetor assembly and the earlier types, one of which may be because
O.S. engineers read this column. I claim that because the Alpha uses an
intake extension with a well-radiused “bell mouth.” I’ve added that
feature onto my customized model engines for years and have shown it
several times in column illustrations.
The other carburetor change is a “reversed layout.” The Alpha .56’s
needle is on the same side as the muffler, with the throttle arm on the
other side. That makes for a compact arrangement.
However, it does mean that a long extension is needed for the
needle valve, to prevent fingers from getting burned by contact with
the muffler. And the .56’s needle has a neat provision for that; it’s a
hole in the end of the needle knob, with a setscrew to lock onto the
extension.
O.S. offers a needle-valve extension-cable set as an accessory. It
has a semiflexible wire cable and a knurled knob. I found that 1/16-inch
wire works nicely for a homemade extension. I form the outer end into
a full loop because I’m tired of snagging things on the usual “bent
angle” end of needle-valve extensions.
O.S.’s Alpha .56 owner’s manual advises using only an electric
starter with this engine. It has no manual “choking” provision. But
especially with a new engine I prefer hand starting (with a leather
glove on in case of a “backfire”). I can get a much better “feel” for
what is happening during start-ups that way.
The Alpha .56 gave me no problems. Instead of choking the inlet I
just blocked off the muffler outlet with a fingertip as I hand-flipped the
propeller. The resulting back pressure to the tank via the muffler
pressure tubing forces enough fuel into the carburetor for a prompt
start-up. The Alpha .56’s snappy compression helped there.
For break-in I used a wooden 13 x 6 propeller. After following
O.S.’s recommended “running-in” procedure (I always read the
instructions), I tached 6,500 rpm at full throttle. That was using 10%-
nitro fuel, with extra castor oil to ensure a minimum 20% lubricant
content. I’ll have more about this topic later in the column.
After a couple more tanks of fuel I managed to get a reliable idle at
just more than 1,800 rpm. With a heavier, reinforced plastic propeller I
think I can reduce that to approximately 1,650 rpm.
The O.S. Alpha .56 runs smoothly. Its short stroke—only 86% of
the cylinder bore—and lightweight ringed aluminum piston contribute
greatly to that. I’m sure the engine’s sturdy, compact design helps too.
Plenty of modelers still fly with 1/2A power. However, fuel for those
little power plants has become hard to find. They need special fuel that
has high nitro content and lots of castor oil.
At least 23% nitro is needed because small model engines have
more cooling area in proportion to their displacement. And a high
castor content is needed because of the high stresses, especially at the
piston end of the rod.
Several readers have asked where to find 1/2A fuel. Byron makes a
25%-nitro, all-castor-lubed blend that works well. (I use that.)
However, Byron’s fuel is not available everywhere. Therefore, I found
an alternative: Tower Hobbies’ Tower POWER 30%-nitro helicopter
fuel, with added castor oil.
Tower doesn’t specify the oil type or percentage used in its
helicopter fuel. Since engines used in helicopters run hot, I assume that
the oil content is roughly 18%. I add 3 fluid ounces of Sig’s castor oil
to a quart of Tower POWER 30% helicopter fuel.
02sig3.QXD 12/20/07 12:28 PM Page 84A quart contains 32 fluid ounces; 18% of
that is 5.76 fluid ounces. Adding 3 ounces of
castor brings the oil volume up to 8.76 fluid
ounces, for a total fuel volume of 35 fluid
ounces. That works out to 25% oil—perfect
for my 1/2As.
The added oil brings the nitro content
down to 27%, but that hardly matters for
sport-flying. An empty half-gallon juice bottle
makes a good mixing container for this
special 1/2A fuel-blending process. It’s
fuelproof and has a big enough opening to
easily accept a piston-type fueling syringe.
I have done yet another offbeat model-engine
experiment, this time with a wooden muffler!
It seems like almost all the model-club flying
fields require mufflers—and have for a long
time. Even the tiny G-Mark .031 of long ago
came with a muffler. Yet many perfectly
usable older engines lack mufflers.
Nobody ever seems to throw those old
power plants away, and I get regular queries
from readers about where to obtain a muffler
to fit, say, a 30-year-old Enya or the like.
Those are difficult to find, and I know of no
sources anymore.
I’ve made several custom mufflers for my
older engines, and it’s not that hard. But I
have metalworking machinery that most
modelers lack.
And through the years I’ve built and flown
several models with closely cowled engines.
In those the exhaust outflow passes directly
over wooden surfaces. The dope finish there
86 MODEL AVIATION
sometimes blistered, but the wood itself never
showed heat damage.
Therefore, I made a wooden muffler to test
on an old Fox .36X. I used pine to ensure
failure—if failure was possible. (Pine ignites
easily.) I ran three full tanks of fuel through
the mighty Fox at full throttle and then took
the muffler off to see what its insides looked
like.
The interior was blackened, but only on the
surface. Shaving off a little wood from the
insides showed that the black went no deeper
than a few thousandths. And the outside of my
pinewood muffler showed no sign of
scorching.
Therefore, I’m sure a model-engine muffler
made from rock maple would work as well as
an aluminum muffler. And aluminum isn’t that
much harder to work with than hard maple.
For another test, using only a hacksaw, a
drill press, and files, from stock aluminum bar
and tubing I made an “exhaust diverter” to fit
an old O.S. .15—one of the early RC types
with a pivoting exhaust restrictor coupled to its
carburetor. The whole job took me only
roughly an hour.
I made this “diverter” to connect to a Fly
Quiet muffler system from Bayou Production.
They are amazingly effective at cutting down
engine noise and cost little. The Fly Quiets are
bulky, but they don’t weigh a great deal and
can be installed inside the fuselage. One built
into a P-47 would let the exhaust come out
from the scale location.
A problem that plagues many modelers—e.g.,
Zach Allerton (New Castle PA) and Jerry
Price (Walsenburg CO)—is gummy
crankshaft bearings. But there’s an easy fix for
that—for glow engines anyway.
Inject approximately a teaspoonful of
Marvel Mystery Oil or Tower Hobbies’ After
Run Oil into the crankcase. Hold the engine
pointing downward and flip the propeller
vigorously. The idea is to make crankcase
compression force the thin new oil out through
the main bearing clearance and flush away the
sticky oxidized oil from that passageway.
Doing the cleanout this way works because
when you hold the engine nose-down, the
After Run Oil (or Marvel Mystery Oil) pools
against the inside front of the case. Then when
you flip the propeller, crankcase compression
will force the After Run Oil/Marvel Mystery
Oil out through the shaft clearance, washing
all the thick, sticky goo out with it.
I’ve used this technique many times with
the various older engines I’ve handled. It
always works—and I’m often amazed by the
amount of brown gunk that is pushed out into
the gap behind the propeller driver.
The reason for hand flipping is that
using an electric starter presses the
propeller driver backward. That might
block the exit of sticky goo. MA
Sources:
Bayou Production
Box 15182
Baton Rouge LA 70895
www.flyquiet.com
02sig3.QXD 12/20/07 12:20 PM Page 86