U I purchased Harry Higley’s All About
Engines book to find out how to set valve
timing on my Gemini 120. I had to disassemble it and replace a conrod but didn’t
pay attention to the timing gear alignment. I found a dot on one gear but not
on the other. It runs but only gives me
6,050rpm with 15% nitro and a Master
Airscrew 15x6. I must have been lucky on
my reassembly. The last third of the carburetor travel, however, gives no response
when advancing to full throttle. Can you
Harry S. Newman
Harry, it sounds like the timing is off and
the engine is only running on one cylinder. Have you tried quickly touching one
of the cylinders to see if it is hot? You
will probably find one cold. Looking at
the engine from the rear with the right
hand piston at top dead center, you will
see a tiny dot on the cam drive gear. This
should align with the hole in the cam
Fuel Flow Issues
U I have a pilot-RC Sbach 342 with a
DLE 55 engine in the nose. In normal
flight, my engine runs great, but when
doing vertical down lines at idle, especially at the pull-up into horizontal flight,
the engine seems to quit and start again.
So, when pulling high Gs on idle, what
can be wrong?
Chris, Vinhedo São Paulo, Brazil
Chris, you have a fuel tank problem. Most
likely, the pickup tube in your fuel tank is
not following the fuel and is allowing the
engine to draw air. Be sure the pickup tube
has not hardened and the clunk is 3/8-inch
from the rear of the tank and moves freely.
If the pickup tube is too close to the back of
the tank, on a sharp pull up the fuel surges
to the rear of the tank causing a momen-
tary richening, which is what you may
be experiencing. Also, be sure that some-
thing is not pinching the fuel line during
sharp pull ups such as the fuel line passing
through a hole in the firewall, and the tank
shifting on pull up.
Gobbling Glow Plugs
U I have a Magnum . 70 4-stroke mounted
on a Hanger 9 Cub that runs great, transitions nicely, but seems to eat a glow plug
every half gallon of fuel or so. The symptom is that the engine will start normally
but sputter or die when the glow driver
is removed. A new plug seems to fix the
problem. Is this normal for this engine
mounted about 20-degrees past horizontal? I use after-run oil (Marvel Mystery Oil)
following each flying session and wonder
if that may be contributing to shortened
glow plug life. I’ve tried Thunderbolt, O.S.
type-F, and Fox Miracle plugs. All seem to
have about the same life span.
Bob, when you say the engine “eats” a
glow plug every half gallon or so of fuel,
I would expect this to mean the element
is gone, indicating that you are just flying
the engine too lean. However, you also say
it just sputters and dies when removing the
starting battery, which would indicate the
element is still intact but contaminated.
Although Marvel Mystery Oil may be the
cause, I have been using it for over 50 years
without experiencing this problem.
U I’m writing this to obtain some information on oil content requirements for the
imported Evolution radial glow-ignition
engines. In your book, The R/C 4-stroke
Engine, you state that, “Generally speaking,
oil content in the 15% range seems to be
sufficient.” I realize that this book was published 27 years ago, but has 4-stroke engine
design changed that much to allow the use
of 5%-7% oil content, as stated under the
product description on the website? The
recommended nitro content is 0%-10%.
Also, will the reduced oil content fuel
allow the engine to produce more power in
comparison to a fuel with 16% to 18% oil?
I understand this engine is a Seidel design
of UMS manufacture in India.
Bob, nothing has changed in the lubrication
O.S. GT 22 ENGINE REVIEW
O.S. just keeps turning out new releases. The latest being the
2-Stroke GT 22 gasoline burner that we would like to bring to your
attention this month. O.S. Engines entered the gasoline market
back in 2010 with its G T 55 2-stroke 3.35ci. engine. (See the July
2010 issue.) This was followed by the GT 33, 2.013ci. 2-stroke
engine that we featured in the May 2012 issue. Now we have the
smallest gas burner in the line, the GT 22, 1.350ci., 2-stroke. I
wouldn’t be surprised if a 10cc, .60-size engine isn’t in the works.
The GT 22 is pretty much a scaled-down version of the G T 33,
utilizing rear induction intake via a reed valve and Walbro-type
pump carburetor. Other specifications include a Bore of 22.0mm
(1.260in.) and stroke of 27.5mm (1.083in.). The engine has an
operating range of 1,800-9,000rpm and develops 2.66hp at
9,000rpm. It swings propellers in the 16x8 through 17x8 range.
The bare weight is 26. 86 ounces and complete with muffler and
ignition module, it weighs in at 35. 24 ounces. The capacitive
discharge ignition module operates on 4. 8-7. 6 volts utilizing either
Ni-Cd, NiMh, LiPo, or LiFe batteries. A nice safety feature of the
ignition module is non-operation below 120rpm. Unless you flip
the propeller smartly, the engine will not fire by just turning it
over—even if the ignition switch has been accidentally left on.
If you have a glow fuel-powered aircraft that has been taking a
big dent out of your hobby fuel budget, gasoline could well be the
answer for which O.S. now offers three different displacement