Magical maintenance methods
A persistent problem with 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-parts dealers.
Cleaning and degreasing
Dawn Power Dissolver (PD) is as powerful 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. 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. 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.
Rust removal
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 and 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.
After-run oil and freeing stuck engines
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 pieces of paper towel, then 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.
I used a heat gun to get the engine hot to help the MMO penetrate. I added more MMO as I continued heating. Eventually I was able to turn over the Cameron, although that took a lot of force. 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.
Eventually I was able to flip the propeller steadily and compress the spring. I left the engine overnight with a little MMO in its crankcase. The next day the engine turned over easily and fired. I ran the Cameron on glow briefly to run the MMO out of the engine and back into the fuel tank. After that the little engine ran perfectly. No disassembly was required. The whole job took me less than an hour.
Nostalgia events and 1/2A engines
Various Nostalgia events for 1/2A-powered free-flight (FF) and control-line (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.
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 single-bypass 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 two main reasons for this: fuel and glow plugs.
Fuel and glow plugs for vintage 1/2As
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-polish-like aroma, remained standard for quite a while. 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 engines 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 similar performance from first-generation 1/2As that they had with their original fuel, it’s necessary to use high-nitro, all-castor-lubed fuel. I recommend Sig’s Champion 25% All-Castor blend. That provides smoother starting and more reliable performance than some commonly available fuels, such as those with 15% nitro and synthetic oil. The little old-time engines will also last much longer running on Sig’s fuel.
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, power output and “startability” suffer. The 1/2As in general need hot glow plugs, and the designed-in-1949 1/2As require long-reach plugs.
Fuel-tank tubing and corrosion
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 bluish-green 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 in the original column shows one result of my forgetfulness: a fuel tank from one of my engine test stands, only approximately four years old, that shows corrosion on the outside brass tubing. 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 searched the web for readily available nylon tubing in the right size, with 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) comes 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.
—MA
Sources
- Doug Martin
Phone: (719) 289-3274 Email: [email protected]
- Model Engine Collectors Association
Transcribed from original scans by AI. Minor OCR errors may remain.
