Recommended fuel mixtures and more
In my April column, we discussed why large engines require less oil in the fuel than smaller engines, and ran an article by Duke Fox on this subject. Duke had written the piece for his “Duke’s Mixture” advertisement that appeared in the August 1969 issue of Model Airplane News. Reader Oscar Furlong did not agree with what Duke had to say. Whereas Duke’s article was based on engineering theory, Oscar Furlong’s letter was based on actual application.
But before we get to Oscar’s letter, I found a major error in Charles Watson’s letter (published in my April column) that those who fly larger, gasolinepowered engines should know about. Charles’s letter mentions having used my fuel mixture recommendation of 32:1 for break-in and 16:1 after break-in, which is definitely wrong. My recommendation has always been to use 16:1 for break-in and 32:1 after. How I passed over this I do not know, but several readers were quick to bring this to my attention. Hopefully, those using my recommendation caught the error.
Oscar’s letter follows:
LUBRICATING OIL MIXES
U I read in your April column that Charles Watson is not comfortable using the 50:1 oil mix recommended by the Ryobi factory and the rule that larger engines require less oil content. I do not agree with this. I currently own a motorcycle/craft repair shop, and for 47 years, I have worked on engines, including gasoline, diesel, and alcohol; two- and four-strokes; and Mazda rotaries. I believe I know that some two-stroke engines require a lot of oil and others only a small amount. It has to do with the design of the engine and the material used in their construction. Let me explain.
An engine with a bushing in the connecting rod lower end and no bushing in the upper end with a cast-iron sleeve and no piston ring will require a 5:1 (20%) oil mix. An engine with needle bearings at both the crankpin and wristpin ends and Nikasil sleeve and chrome-moly piston ring will be happy with a 50:1 ratio, and with a good oil, such as Klotz, it will be fine with a 75:1 mix. I have a friend with a DL120 in an Extra 300 using a 100:1 mix with no problems. Most modern-day gasoline engines run well with a 50:1 mix, but I have a 35-year-old Honda motorcycle with a cast-iron sleeve and two hard steel piston rings in which I use a 25:1 mix. I think no one is going to reinvent the wheel, and if Ryobi says “50:1,” then use 50:1. If O.S. says “20%” (5:1), then use that. They know how they make the engine.—Oscar Furlong, via email
Answer: Well, Oscar, the design of an engine and the construction materials used make a big difference in the amount of lubricating oil the engine requires. As I have said many times over the years, an engine with a ball-bearing-supported crankshaft can use less lubricating oil than one with a sleeve bearing. The same for the connecting rod: An engine with a rod with bronze bushings in the crankpin and wristpin ends can use less lubrication than one without bushings. However, with all things being equal, as the displacement size increases, the required lubrication decreases—which is what Duke’s article was about.
RECORD-SETTING CONTROL-LINE FLIGHT
U Given your association with Veco and K&B, did you have any input on the mid-1950s’ record control-line flight (24 hours) using a Veco .35? Was the engine stock? Did it boost sales? Did it really matter in the progression of engines and sales at the time?—Len Rozamus, Hopewell, Virginia
Answer: Len, I only have a vague recollection of the occasion and cannot say if the engine was stock or one I had assembled. Undoubtedly, it would have helped engine sales at the time, as do major contest wins. One thing along this line that I do remember is the time when Lou Andrews won the 1950 control-line Nationals using a Fox 35. Duke’s engine business had been struggling along until Lou’s win, and after that, his business skyrocketed. Duke later confided in me that he had made $50,000 in sales afterward, which he put away as his “nest egg,” never to be touched until his retirement. That was big money back in those days. Personally, I experienced the effect of contest wins when Doug Spreng won the
1960 Nationals pattern event with one of my Lee 45s. I was immediately swamped with more orders than I could handle, which resulted in my selling the design to Henry Engineering. This engine became the Veco 45. Then, when Cliff Weirick and I won the 1964 Nationals pattern event with the
first prototype 61, of six engines I had built, the first production run of 1,200 engines sold out overnight as did the second run. Before the win, Veco had been afraid the engine might not sell due to its $60.00 selling price.
LEE SPECIAL?
I have been reading your column since the mid-’80s, when I got back into model airplanes. I just purchased a K&B 61 at a swap meet.
The seller told me that this engine was a Lee Special. How do I confirm this? The engine has a Perry carb, a pump at the rear, and an aluminum screw-type plug halfway up the rear of the crankcase. The serial number is A0014679. From the info in your column over the years, the MECOA website, and other sources, I believe it is a Lee Special.—Ray Murry, Floresville, Texas Answer: Ray, engines purchased directly from me will have “Lee Custom” stamped on the left-hand mounting lug and my own serial number on the side of the lug. Those purchased elsewhere and sent to me for the Customizing/Blueprint procedure will have “C.F. Lee Mfg.” on the top of the lug and a factory serial number as yours has. Without my stamps, the engine is not one I worked on.
SCREWDRIVER QUANDARY
In your “All Screwed Up” letter in your last column, the reader’s question involved the poor screwdriver fit with some Phillips screws. The problem may be using our standard Phillips screwdrivers on what could be screws made to the Japanese Industrial Standard (JIS). These have slightly different tines and point angles.—Les Schjelderup, Coal Valley, Illinois
Answer: Thanks for the info on Japanese Phillips-head screws, Les. I was not aware of this. Like they say, “You are never too old to learn something new!”
THIRSTY ENGINE
I bought a new Super Tigre
.40 glow engine and put it in an Avistar 40 aircraft. I can’t hand-start the engine; all it does is throttle up and stall out. The compression is also kind of soft. I unbolted the piston head on top and retightened it, but it still won’t start. I’ve heard those Italian engines are supposed to have soft compression and that the piston rings are intended to heat up to seal off to create hard compression. My friend has a
1978 Super Tigre .40 glow engine. It has a lot of compression. I can hand-start it, but I noticed it does not have piston rings. They say you need an electric handheld starter over the prop, but I’ve seen those engines start up by hand. Do you know the problem with my new Super Tigre .40 engine? They no longer manufacture the Super Tigres in Italy and, instead, make them in China. Is this why I can’t hand-start it?
Also, I made my first home brew of model glow fuel in a 1-quart plastic jug with 2 1/2 bottles of methanol alcohol and added 3 1/2 ounces of castor oil. Would my new Super Tigre run with 3 1/2 ounces of castor oil to a full quart of methanol alcohol? Is there enough castor oil in the mix?—Chris Roberts, via email
Answer: Chris, your letter puzzles me. You say the engine will not hand-start and then it starts up and stalls. It is evidently starting up by hand, and your problem is that it is not getting enough fuel. Have you tried opening the needle valve a couple more turns? If you have, then something is blocking the fuel, such as a plugged-up filter or something pinching the fuel-tank vent line. Why your friend’s engine is working OK I cannot explain without being able to examine the engine. The reason the 1978 engine has more compression than yours is because it’s a lapped-piston design and yours is ringed. I have received quite a few complaints about the Chinese ringed engines being low on compression; they take quite a bit of running before the ring finally seats. If properly made and fit, a ringed engine should have excellent compression. Part of your problem may be the home-brew fuel you are using. Three and 1/2 ounces of castor oil to a quart (32 ounces) is only 11% oil. You should be using 18 to 20% oil, which would require 5.8 to 6.4 ounces of castor. This, in itself, would improve the ring seal, which would greatly help the starting and overall performance. Your engine was also intended to be run on 10 to 15% nitromethane, which, again, would improve the starting and performance.