The Building Board: January 2010

Is your reed valve engine giving you fits when it comes to reliability or duration? Try this link from New Zealand or this one from R/C Universe.

Bill Schmidt gives some advice on fuel:

The Cox ½ A Texaco engine — Bill Schmidt

I have sat on the sidelines for sometime watching and reading all the brickbats and dissention over the Cox reed valve engine used in the 1/2A Texaco event. This has been going on for years. People either want to get rid of the things because they are fussy and their results with them have been very frustrating, or they seek constant rules changes to alleviate what they perceive to be the problem. I remember quite well back in the early 80’s when many time grand champion Bruce Norman, (remember him) refused to have anything to do with them because they were so aggravating. He was not alone either then or now. Let’s talk about this a little bit and look at some facts.

I am the person responsible for the factory produced 1/2A Texaco engine first brought out by Cox in 1988. The engine came about as a result of conversations with the then Cox owner, Bill Seltzer, at the Toledo shows. It took two years of push and shove as he initially laughed at the idea. I said, “come up with a special box and use selected existing parts of perhaps a

different color combination, and let marketing take it from there”. One day the phone rang and Bill said “let’s do it”! He put Larry Renger in charge of liaison with me to make sure an optimum product would be developed. The first ten engines sent to me were the large 10 cc tanks with a .055 carburetor throat, std. low compression head and no colors. The rules change to use the 5 cc tank was still in the future. I enlisted the help of fellow club member, the late Dean Zongker, to help me sort things out.

We flew these engines in a 300 sq. in. nimbus that could handle the Kansas wind extremely well. We would fly the power portion of the flight only, and spin down rapidly to conserve battery after the engine ran dry. This went on for a couple of weeks until both of our wives began to raise heck about the exercise, and being gone all the time. Looking back we should have told them we were engaged in a money making secret project. Anyway, the first thing we learned was that an .055 carb did not work well. You were always chasing the needle valve trying to get a steady run. I called Larry every day or two and kept him posted on the results.

I suggested that we go to the stock .0625 carb throat and things worked out fine at that point on. The design was frozen at that time and Cox started producing the engine. I had nothing to do with the large fin special glow head that came out with these engines, and feel that they addressed a problem that didn’t exist. I did however, strongly suggest to Bill Seltzer that the fuel tank or some part of the engine be anodized a brilliant purple color. This was due to my knowledge and exposure to the 1950 O&R .60 with the purple head and its effect on people. These engines were beautiful and much sought after by collectors. I was overruled and the Texaco engine came out as you know them today. I however, was not to be dissuaded, and had 10 tanks and crankcases anodized purple by the folks who did Cox’s color anodizing for them. I flew one to victory and also grand champion at Seguin, TX in 1987. I still have them as a memento of this experience. Now to the purpose of this treatise. The primary reason that people have so much trouble with the Cox reed valve engine is because they are ignorant of what they are dealing with in the physics of its operation.

I strongly suggest that you take a clean tank back plate by itself, and attach a 6 inch length of fuel line to the fuel line attach nib. Now screw a std. needle valve into the back plate to the fully closed position. Open the needle valve 1 turn out and suck on the 6 inch fuel line with your mouth. This exercise will give you a vivid idea of just exactly what is happening inside this engine when it is running. That’s an infinitesimal rate of flow that is going through this engine in its normal operation. In fact, one wonders how it functions at all. By the way, the ¾ to 1-1/2 turns open is where you want to be for a good performing ½ A Texaco engine. If yours requires a greater opening than this after break-in, then you need to switch piston/cyl, back plate or orally check the reed valve for a perfect one way check valve operation. It must check very positively when you blow on the reed retention area and it must flow air very freely when you suck on it. Suck and blow very rapidly to observe this action. Say, 7300 times a minute! The reed must not squeal when you blow it shut! Replace it if it does. The mylar reed must be perfectly flat as viewed in reflective light. So much for the understanding as well as the prerequisites for what it is that you are trying to do.

Now we come to the good, (arcane ) part of this exercise. What do you think small particles of dirt in the fuel do when they encounter the needle valve with its extremely small rate of flow capability. That’s right! It gives you fits and makes you cuss and throw your transmitter on the ground! Settle down and listen up because there is a cure for this problem. Strain your fuel 2 or 3 times through a coffee filter and funnel into a ½ or 1 pint liquor bottle!!! Okay now, I know there are people out there who have issues with that, and won’t have, or tolerate a liquor bottle in their house. I have some fellow club members who feel this way. I don’t know exactly what to tell you as an alternate because nothing else works as well. You don’t even have to go into a liquor store to obtain one. I go to the nearest public park and select from the ones I find there. Don’t use the cheap plastic ones because they are milky and exhibit poor optical quality. Some guy used to throw a really nice Gordon’s ½ pint gin bottle into my front yard at night several times a week! This was really appreciated, and saved me a lot of trouble obtaining good fuel bottles. The bottle must be clear glass and narrow, not round, for good viewing in the sunlight. Wash it out and check the fit of your favorite hypodermic needle before you go any further. The same size bottles vary widely in their neck I.D. Precision manufacturing I guess. One liquor store owner asked me to please leave after I came in with a dial caliper to measure the necks on the ½ pint bottles When you discover the best bottle remove the labels by soaking in hot water. Get it very clean and use lacquer thinner if need be to remove the last vestiges of the labels. After filtering your fuel as above hold the bottle up to the sunlight and look for tendrils and flotsam swimming around in suspension.

You will be in for a surprise at how much there is in the fuel. It is hard to get it perfectly clean at times. What you do is get it as clean as you can, and then let it set (settle) for a day or two. I have never understood where it comes from, but in a weeks time if you shake the bottle, hair like tendrils and other particles will be disturbed and rise up in the fuel when held up to the sunlight for viewing. This debris seems to thrive and actually grow in the fuel. What I do is strain the fuel a few days before an outing and do not disturb it in transport to the flying field. Keep the bottle upright in some manner in your flight box or elsewhere. If you really have to win the event that day, then just find a way to visit your competition and shake up their fuel cans! I can’t imagine anyone flying 1/2A Texaco with fuel from a can, and you won’t either after you do what I have suggested. I do not use castor oil fuel and only 12 to 15% synthetic as well as about 7-8% nitro to keep the fires lit. You will not varnish up if there is no castor present. Do not break in an engine with this formula, use standard fuel for this. Be advised that this formula can also wipe out a main bearing in rainy conditions, but will give you the longest engine runs you can get legally under normal conditions. You must use after run oil after flying with this fuel.I strongly suggest using only Shaler Rislone brand engine oil additive obtained at an auto supply store. Be sure and work it well into the main bearing right behind the prop drive washer. Propeller? I swear by the Cox gray 8-4 plastic even though it is cast with the blades 178/182 degrees from each other. Didn’t know that? Just put the prop on its side on a flat surface, and then flip it over on its other side and notice the difference in the two heights. Run it on your engine one way and then turn it 180 degrees and see if it is smoother. Put it on the way it runs the smoothest. You should get 7300 rpm on a standard day. A stellar engine is one that turns over 7300 with a nv opening of ¾ -1 turn open. If while you are testing engines, you find you have a nv opening in excess of 2-2-1/2 turns then stop. You are wasting your time with that engine. Old, used Babe Bees are plentiful and are your best bet for a good runner. Believe it or not, the early Babe Bee with the single bypass port, and somewhat narrow exhausts with no sub piston induction is capable of some really good performance. These are the engines found at the bottom of the barrel. Keep your glow head tight and go get ‘em.

Bill Schmidt

Bob Erpelding on the motors

A Guide to ½ A Texaco Engines

The rules say a Cox “stock” reed valve.049 engine with integral 5cc tank. No diesel conversions or throttles allowed. The only modifications are: Moving the fuel pickup from the middle (control line setup) to the bottom of the tank, addition of a muffler, and addition of a needle valve extension. As the object of the event is to put in a 15 minute flight with a full tank of fuel and the engines will run, on the average, 2 to 3 minutes on a full tank we must investigate what can be done to reach the 3 minutes or more without sacrificing performance.

Starting at the top we have the glow head. A trip to a well stocked hobby shop will find several choices. The recommended one is #315 the “Texaco” which can be identified by the five fins. This will fit on any of the engines. Next choice is the standard head with 3 fins and a smooth top surface. The one to avoid is the high compression head which can be identified by axial lines scribed on the top surface. It can be used, and will give more power, but your run time will be shorter and it will be harder to needle with low nitro fuels. A good NiCad will get it lit; some power panels will burn it out. We personally use a 2 volt sealed lead acid battery with about 2 ft. of zip cord and the Cox clip and have had no trouble burning out plugs. Just be careful as the glow heads are expensive.

Moving right along we come to the reed valve which can only be reached by removing the four screws in the back plate and pulling off the tank and back plate assembly. On the newer engines the crankcase gasket and the reed retainer are one piece and there isn’t much to do other than check that the reed (the little clear plastic rectangular piece) is intact and clean. A speck of dirt here can cause the reed not to seal and give you fits trying to start or run. The older engines had a separate paper gasket, a circular wire reed retainer, and a clear plastic as above, or thin metal, star shaped reed. The front of the tank is different in that it has a groove to accommodate the reed retainer so it is not usable with the newer style gasket/retainer. The wire retainer has a crossbar which is slightly offset from the ring. This offset must be located away from the reed and toward the crankcase. The metal reeds are very easy to damage, no longer available, and probably should be replaced with the newer plastic style unless you have had experience handling them.

While we have the tank off, check the plastic fuel pickup tube. If it has turned hard or fallen off nipple replace it with a new piece of plastic tubing. For small tank, fuel line should be 1 ¼ inches long. Make sure it goes to the bottom of the tank and does not get pushed out of the way by the venturi or tank screws when you reassemble. Do not use silicone here as it will probably come off at the least opportune time, like 1 minute into your last official flight. Also check the small “O” ring found on the rear of the venturi running through the tank. THIS PART IS VITAL. If missing or damaged the engine will not run. The “O” ring is a part of the Cox overhaul kit. Carefully put everything back together and we should be ready to run.

If you are working with a new engine fit a small (5-3, 5-4 Cox gray or black) propeller and run several tanks full through at a rich needle setting. After a few tanks full lean out the needle briefly during the run. When you can hold a lean setting without sagging or quitting you are ready to switch to your larger flying prop, usually a 7-3.5 or 8-4. You may have to go through the above procedure again before it will hold a lean setting. While this may seem like a lot of work, most of these engines need a lot more running in than anyone wants to admit and improve a lot with more time.

Fuel, Cox red can (10%) if you’re pretty sure its fresh, any good 10% nitro fuel preferably with some castor oil in the mix. Cox racing fuel or other high nitro fuels are not recommended as they will shorten your duration. Some folks use all synthetic oil and even 4 cycle fuel with reduced oil content. If you want to experiment go ahead, but be advised it may shorten your engine life. The folks at Cox like a little castor.

Alright you have gotten this far and the engine is running, but how well, you ask. If you can get it to run in the 5 minute range consistently, tach about 9,500-10,000 on a 7-3.5 prop, or 7,000-7,500 on an 8-4, you have a keeper. Anything less than this is marginal and you may want to check it out some more or look for another engine. These engines are not all created equal. Larry Davidson, past Grand Champion, wrote a couple of years ago of going through 15 engines to find 2 that measured up. That may be part of the price of winning. It still takes a good flying airplane and a little help from the “Thermal Gods” too.

One last piece of advice, if you cannot get your engine running with a few healthy flips or a couple of very brief blips with an electric starter as a last resort, something is wrong. Start checking glow head, fuel, needle, battery, etc. If need be, the engine can be disassembled on the field with nothing more than a screwdriver, the Cox wrenches, and a rag to lay the parts on. The smallest bit of dirt in the system will give you trouble like you can’t believe. We see guys grinding away with the starter or flipping forever. All this does is wear out the engine or your fingers.

The Building Board

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