Mufflers, Multi-Cylinders, and More
Email your questions to Clarence Lee at MAN@airage.com.
It seems like, lately, a month or two seldom goes by in which one of the major hobby-related businesses doesn’t close its doors. In the past six or seven months, Fox Manufacturing ceased operation, as did Hobby People with their multiple stores and Macs Products, the country’s largest manufacturer of mufflers, tuned pipes, header pipes, and related accessories. It was back in the mid-1960s that the change from .45ci engines to .60 size for pattern competition was underway. Due to the larger engines, noise became a problem at many flying sites, and many clubs began looking into mufflers as a solution. Wally McAllister foresaw the future and formed his business, Macs Products. After more than 40 years, Wally decided to retire and turn the business over to his brother, Dave. This past September, however, Dave unexpectedly passed away. When no other family members were interested in continuing the business, Dave’s wife put it up for sale. My good friend Randy Linsalato, who in conjunction with his wife, Anching, own and operate MECOA/K&B, purchased Macs Products. Randy does not intend to continue any production, but he did receive a large inventory of the products that he will be making available. So if you are in need of any of the Macs Products’ line of mufflers and pipes, visit mecoa.com or call 626-359-6972.
Now to the letters.
am wondering if you could enlighten me and your readers about the design of multi-cylinder engines and, in particular, radial engines. Why do radial engines always have an odd number of cylinders? The only even number multi-cylinder engines I have seen are always opposed.—Frank Jordan, Kansas City, KS
Answer: Well, Frank, as most people with any engine experience know, a four-stroke engine fires every other revolution (i.e., two revolutions for one combustion cycle). In the case of a 5-cylinder radial, the number one cylinder fires, skips number two, and number three fires, etc. On the second revolution, number two fires, followed by number four, and back to number one. Since the engine fires one cylinder and then skips one, there has to be an odd number to come out even. Radial engines use a master rod, with the other rods connected to the master rod and a single throw crankshaft. Opposed engines use a double- (or more) throw crankshaft depending on the number of cylinders (i.e., a throw for
each pair of cylinders).
Our next letter from Canadian Ed Carew was accompanied with two photos, neither of which was suitable for reproduction. Basically, they showed a piston with a big hole in the center and both rocker arms broken. Ed’s club members felt the damage was caused by a stuck valve, but he disagreed and asked for my opinion. Read on.
I have been reading your columns for more years than I can remember, and this is the first time I have written to you. The subject matter is a 15-year-old Saito .56 engine that quit abruptly in flight.
The engine had previously been very reliable in a number of different models, including a Telemaster, Unionville Beaver, and Kaos 40. There has been a lot of discussion in our club regarding the cause, with “stuck valve” being the most popular view. I have a problem with that since it does not explain the damage. I think the valve broke off the valve stem, bounced around the combustion chamber and made a hole in the piston, jammed the exhaust valve (thereby breaking the rocker), then was pushed up into the intake port, which pushed the valve spring assembly out and broke the other rocker. This would account for the damage, but what would cause the valve to break off the stem, and what would cause the retaining clip to break and the top of the valve stem to break off? With your many years of experience, I am hoping you can provide an explanation of what might have caused this failure. Note: I don’t think it is worth repairing the engine; I’m just curious about what happened.— Ed Carew, Carleton Place, ON, Canada
Answer: Ed, in my opinion, I believe your assessment is entirely correct. The damage had nothing to do with a stuck valve. You did not say how much fuel had passed through the engine, but having seen use in three aircraft, it was probably a lot. During that time, it more than likely saw some lean running, particularly toward the end of a flight, resulting in detonation. Detonation is a well-known cause in the automotive and full-size aircraft fields for breaking valves and pistons.
Our next letter is a little on the long side, but expresses a problem that I am sure many of our readers have experienced when trying to disassemble an engine for cleaning.
I have read all of your Engine Clinic articles, starting with the first one way back when, and also your various books on engines. I have had a problem with an old Super Tigre .51 BB engine, which I would like to get your advice on. I cannot recall your ever addressing this issue, except to mention that, on this type of engine, the wristpin must be pulled out with a wire using a hook on the end. It would appear that this engine was given Rislone after-run oil many years ago, as it has greenish marks. I would guess that the engine has not been used for more than 25 years or more. The engine was nearly stuck but would turn over. I put 3-in-1 oil in it, and it freed up pretty well. The cylinder sleeve came out fairly easily.
Then came the problem. First, I tried using the wire to pull the pin but could not even get the end pad out, even after heating the piston. I inverted the engine and filled the piston cavity with WD-40 and let it soak overnight, with no success. I tried heating it several times—again, no success. The rod was loose on the wristpin, so the pin had to be stuck in the piston. I also tried your carriage bolt trick to pry the rod off the crankpin, but there was not enough slack as it would only come about a third off and I had to tap it back into place. I then turned to a drastic method. I carefully drilled a hole in the front of the case at exactly the same position as the back hole. I used a slim flat-head punch through the front hole and carefully tried to tap the pin out, but it would not move. I then used a press and finally got the pin to move. It took considerable force to push the pin out of the piston. I was concerned that the pressure used might distort the piston, but it seems to be OK. After cleaning the piston and wristpin, they seem to have the proper slip fit, so it seems that the pin was stuck with dried oil.
Do you think the Rislone could have possibly caused the stuck pin? I have not encountered this problem in any of my engines that have been stored with Rislone. Do you have any ideas as to how to remove a wristpin that is as stuck as this one was? I would appreciate any thoughts you have on this problem. I know you can cut the rod and get the parts out, but with no replacement rod, that is not something to do.—James Leisk, Shreveport, LA
Answer: Jim, I can sure relate to your wristpin experience as I have run
into this many, many times over the years. If you ever run into this problem again and can’t remove the wristpin with the tip of a bent pin, use the tip of a round jeweler’s file jammed into the wristpin hole. If this still doesn’t work, the end pad will have to be drilled out. Then using an Easy Out, available at any hardware store, will be required. Easy Outs usually come in a set of four. Easy Out, along with heat, will usually get the wristpin out. Rislone is a good oil to use for long-term storage but, like oil, will eventually harden. I do not like it for an afterrun oil as exhaust residue will stain white or light-colored paint when the engine is run. I have found automotive automatic-transmission oil to be much better for long-term storage, and when mixed 50:50 with Marvel Mystery Oil or Air Tool Oil, it’s an excellent after-run oil.
MULTIPLE ENGINE FAILURES
I have been flying RC aircraft for about 16 years, mostly with O.S. two-stroke engines. All was going well until about a year or so ago when l started to have multiple engine failures. Up until that point,
I was the envy of our flying-club members as I rarely crashed an airplane and still have, and occasionally still fly, my original SIG Kadet trainer with an O.S. .46 engine. Last summer, I totaled three very nice airplanes, severely damaged another one, and managed to dead-stick glide a few more back to the field with no damage. In all cases, all of these glow engines (five different 0.S. engines and one Evolution) just stopped dead, usually in level flight. I have no idea what’s going on!
Any suggestions? I love the RC aircraft hobby, but all this is leaving a sour taste in my mouth.—Dick Parkes, Kamloops, BC, Canada
Answer: Dick, if you experienced the same problem with five different O.S. engines and an Evolution engine, which have proven to be some of the most reliable on the market, you obviously have a common problem that you are overlooking. Two-stroke glow engines are pretty simple in operation, and if they’re mechanically OK and supplied with fuel and ignition, they are going to run. In your case, I would have to guess that it is a fuel-related problem. I believe your problem is either a stiff pickup line in the fuel tank that is not following the fuel as the tank empties or you have a blocked or pinched muffler pressure line creating a vacuum as the tank empties that, in turn, stops the fuel flow.
INTAKE AIR LEAK
I am trying to catch up with my reading and just finished reading your column in the February 2017 issue. The “Hard Start” section drew my attention as I have run into this difficulty before and found that the source of the problem was air leakage in the intake header/manifold downstream of the carburetor. The engine would run quite well at top speed but would lean out at idle to the point of being impossible to start at that throttle setting. Thanks for all the valuable knowledge that you have been passing on to your readers over the past 48 years.—Guy Lemieux, via email
Answer: Thanks for sharing your experience with us, Guy. It is always appreciated when our readers can help us solve problems.
That does it for another one, gang. We’ll be back in the December issue.
Macs Products’ universal muffler is available for .20- to .60-size engines with either a strap-on or bolt-on retainer, depending on the engine.
The 1945 Morton M-5 was the first radial engine to be marketed for model aircraft use. It weighed only 22 ounces and developed about 0.5hp at 3,500rpm. It was modeled after the full-size LeBlond engine and was developed during World War II as a training aid for aircraftengine mechanics.