The Engine Shop - 2010/02

A PERSISTENT PROBLEMwith our
model airplane engines is keeping them clean,
rust-free, and not sticky internally. That’s
often more troublesome than we might
expect, because the best lubricant for these
power plants—castor oil—congeals with time
and especially with heat.
Its highly adherent film between moving
parts thickens inside stored-away engines.
Eventually, it glues them together.
Castor oil on the outside of an engine
becomes sludgy. On hot parts it caramelizes
into an ugly brown coating that used to defy
all efforts to remove it. Rust also presents a
perennial problem.
However, the situation is better now. You
can find inexpensive and effective model
engine-cleaning compounds at Wal-Mart and
auto-part dealers.
Dawn Power Dissolver (PD) is as
powerful of a grunge remover as any of the
compounds that used to be sold for cleaning
these engines. Yet PD is water-based, emits
no dangerous fumes (I find its aroma
pleasant), and costs less than $3 for a 12.8-
fluid-ounce squirt bottle.
PD attacks paint, but that can be helpful.
I’ve used it to strip old paint from the heads of
McCoys and K&Bs of yesteryear before
repainting them with modern engine enamel.
84 MODEL AVIATION
Brass tubing isn’t the best long-term option in a glow fuel tank.
Brass catalyzes methanol into acetic acid. Nylon tubing is immune
to this problem.
Old-time 1/2A engines such as this Baby Spitfire (in a Veco
Dakota’s nose) were designed differently from more modern
1/2As and require special plugs and fuel.
Complete paint removal requires several applications.
If PD is left too long on a matte-finished model engine exterior, it
can leave a dark, grayish stain behind. But when that has happened on
one of my engines, I’ve been able to remove the stain with a stiff
toothbrush and a mildly abrasive household cleanser such as Comet.
Now for rust. I’ve mentioned Evapo-Rust (ER) in a previous
column and reported how it amazingly restored, to runnable
condition, the most horridly rusted—inside and out—Fox .36 I’ve
ever encountered. It also removes rust from tools, music wire, and
anything rusty.
Unlike other rust removers, ER is not acidic. In fact, it’s utterly
nontoxic and noncaustic. It works by reversing oxidation, via a
chelating process. In doing so, it restores rusted metal to close to its
original finish. This product is reusable too.
ER used to be hard to find. Now most AutoZone stores carry it.
The accompanying photo shows you what to look for on the shelves.
The earlier packaging was much harder to distinguish.
While you’re at the auto-parts store, buy a can of Marvel Mystery
Oil (MMO). It’s the best after-run oil I’ve used.
MMO serves a triple purpose; it’s a solvent, a penetrating oil, and
a rust preventer. Squirting it through an engine’s spraybar when
you’re finished flying will keep castor oil from restricting fuel flow.
Spritzing the liquid into and around your carburetor barrel will
stop stickiness there and relieve the throttle servo of much work.
Inside an engine, MMO blocks rust and keeps castor from
congealing.
I use this product for freeing up old engines, which precludes the
need to take them apart. I recently did this with a 1959 CL Cameron
.15 that had been stored after a flying session—and left idle for more
than 40 years.
I plugged the Cameron’s intake and exhaust with tightly packed-in
pieces of paper towel. Then I cleaned its exterior with PD. After
drying the engine, I removed the paper towel plugs and squirted
MMO into the ports. At this point, the power plant was still firmly
glued together internally. Its piston and shaft were immovable.
Then I used my heat gun to get the engine hot. That helped the
MMO penetrate it. I added more MMO as I continued heating.
Eventually I was able to turn over the Cameron, although that took
a lot of force. But it became easier with each additional revolution of
the propeller. Soon I could flip the propeller through slow rotations.
At this point I employed my “secret freeing-up technique.” I
injected roughly a teaspoonful of MMO into the Cameron’s intake
and turned the propeller to let that oil flood the case.
Then I held the engine with its propeller pointing vertically
downward and vigorously flipped the propeller. Crankcase
compression forced the MMO that was pooled against the case’s front
interior out through the clearance between the shaft and the bearing.
That action washed the congealed oil out, and all stickiness gradually
vanished as I continued flipping.
Now that 50-year-old Cameron .15 is as perky as it ever was in the
previous century. And no disassembly was required. The whole job
took me less than an hour.
Various Nostalgia events for 1/2A-powered FF and CL models have
become popular. There is the annual All-Dakota Fun-Fly at the AMA
Nats and CL events for Walt Musciano’s designs. These are restricted
to earlier-model 1/2A engines, a considerable number of which have
survived.
Yet there’s one vintage 1/2A engine still being made today: the Fox
.049, which is custom-assembled by Doug Martin. He has several
versions available: single and double bypass, with or without an
attached fuel tank, and with different-style cases. Only the singlebypass
models are Nostalgia-legal.
Plenty of OK Cubs, Anderson Baby Spitfires, and K&B Torp
Juniors still exist. Yet, judging from a considerable number of
readers’ queries, getting those early 1/2As to perform as sweetly as
they did originally can be difficult. I’ve found that there are two main
reasons for this: fuel and glow plugs.
When the first 1/2As came out in 1949, two types of glow fuel
were available; neither used nitromethane. One kind of fuel was a
blend of gasoline, “motor oil,” and nitropropane. The other was a
mixture of methanol, castor oil, and nitrobenzene.
Nitropropane fuel quickly went off the market, but the other,
which today’s old-timers remember well for its shoe-polishlike
aroma, remained standard for quite awhile. It’s the fuel that Cubs and
Baby Spitfires were designed to use.
Nitrobenzene is far more potent than nitromethane. That’s why
many CL Speed records were set with fuel containing it.
Unfortunately, nitrobenzene is also highly poisonous and a likely
carcinogen. The AMA forbade its use in model airplane fuel long ago.
To get the same performance from first-generation 1/2As that they
had with their original fuel, it’s necessary to use high-nitro, all-castorlubed
fuel. I recommend Sig’s Champion 25% All-Castor blend. That
ensures much easier starting and more reliable performance than with
the more commonly available fuels, such as those with 15% nitro and
synthetic oil. The little old-time engines will last much longer running
on Sig’s fuel as well.
As for glow plugs, until 1950 there were no short-reach versions.
Now there are many—and it may seem logical to use one in a Cub or
a Baby Spitfire. That seldom works. When it does, the power output
and “startability” suffer.
02sig3_00MSTRPG.QXD 12/21/09 11:24 AM Page 84
The 1/2As in general need “hot” glow
plugs, and the designed-in-1949 1/2As require
long-reach plugs.
In a couple of past columns, I described
how metal alloys containing zinc cause
methanol to catalyze into acetic acid.
That’s mighty corrosive stuff. It causes
steel to rust and brass to convert to bluishgreen
“verdigris.”
I’ve known this for years. I’ve usually
known better than to use brass tubing in
model fuel systems. But sometimes I forget,
and too often there’s no good alternative.
A photo shows one result of my
forgetfulness. The tank is from one of my
engine test stands, only approximately 4
years old. But what’s the alternative?
Brass tubing has long been standard in
Sullivan and Du-Bro model fuel tank kits.
Some of those also included nylon tubing
for a while, but evidently not anymore.
True, nylon tubing is more difficult to
bend accurately than brass. However,
careful heating with a hot-air gun helps
greatly with that.
I’ve “surfed the Web,” searching for
readily available nylon tubing in the right
size, with an adequate wall thickness, to fit
model fuel tanks. All I could find was the
outer tubing from Sig’s Nylon Tubing
Pushrods. The plumbing from some ARFs
and helicopters (such as Hirobo) come with
prebent tubing that has been chromed for
protection.
The only other thing I can suggest as a
preventive for corrosion in model fuel tanks
is to pretin, with solder, the outside surfaces
of the brass fuel tubes before assembling
them in their tanks.
Doing that won’t help the tubing
insides, but luckily those don’t seem to be
affected as much as the outer surfaces.
Look at that photo again. MA
Sources:
Doug Martin
(719) 289-3274
[email protected]
Model Engine Collectors Association
www.modelenginecollectors.org