|
While reading
through the various News Groups and Mailing Lists that pertain to R/C models,
I am never ceased to be amazed by the steady stream of the same general questions
on the operation of these great powerplants. I find
it hard to believe that so many modelers don’t have the instructions that
came with the engines, or perhaps they just don’t want to read them J The first thing you need to realize is that
our four-stroke model engines operate the same as a modern turbo-jet engine.
The Suck, Squeeze, Bang, and Blow principle was discovered by professor Wolfgang Flugelheimer in 1898 (Source BNN) I’ll
attempt to sort through the basics here and now. As a matter of background,
my first four-stroke was an ancient O.S. .75 – exposed valves and all – acquired back in 1984. While it
certainly wasn’t a powerhouse judged by today’s standards, it operates the
same and is maintained the same as any of the new ones. Along the way,
I’ve operated the following four-strokes: In the O.S. family, my smallest is
the .26; the largest is my 3.00 Gemini Twin. In between, I’ve had a old 1.20, a 1.20 Gemini Twin, and a 1.60 Gemini Twin. My
Enyas include the .46, a .53, a .80, and (still
N.I.B. waiting for a project) a 2.40 V-Twin. My only Saito is my .91. I also
recently have started to fly a Y.S. .53 and a Laser
.70. I also have a new Laser 1.20 just
about to go into a scale project. Without
hesitation, I can state that I recommend any of these engines. I have had
nothing but excellent operating results and wonderful service from their
respective service centers. I have not even thought about any of the clones
coming along; I’ll stick to the originals, thank you! The extra cost is worth
it. The most
frequent questions I see are “What fuel do I use?” or “Do I have to use a
different fuel?” The answer to the latter is simply “No.’ HOWEVER, if you use
your standard two-cycle fuel, HOW you set your needle valve
becomes more important. We’ll touch on that later. Generally speaking,
though, you have to buy fuel anyhow; why not use a high quality fuel
formulated for four-strokes? I can’t speak
for the fuel manufacturers, but I was told that the original four strokes had
somewhat higher compression to compensate for their power shortages. As such,
they were subject to detonation and a reduction in total oil content helped
to alleviate this problem. How true this was, I can’t say, but it just
doesn’t hold true today. I have always
trusted noted writer for R/C Modeler and engine Guru Clarence F. Lee, and
ever since I first read of a fuel formula he recommended for four-strokes, I
have used it. It has been revised several times, but currently he still
recommends this custom blend (by volume): 15 % Nitromethane
(10 or 12-1/2% OK), with a total oil content of 18%, OF WHICH 3% is Castor
Oil, 15% Synthetic. C. F. Lee goes on to say that he prefers a total oil
content of 20%, which is 18% Synthetic and 2% Castor, but if one is not a
“needle tweaker,” you can go down as low as 17%
total oil. He likes “Klotz KL-200 Synthetic Oil,”
by the way. Here’s a
WARNING from Mr. Lee, and I quote: “A lot of the fuels on the market nowadays
are running in the 16~17% range of oil, and this is
by weight, not volume. As a result, a lot of guys are burning up their
engines running them on the lean side.” This is for both two and four stroke
fuels. I started out
getting my fuel custom blended for me from F.H.S. Supply, http://members.aol.com/FHSoil and I still do. I’ve never had a problem
with their Red Max brand in fifteen years, and they provide excellent
service. Now that we
have the fuel, how do we get it to the engine? For starters, let’s install a DuBro Filter/Clunk (part #161) at the end of our fuel jug
pickup line, keeping it at least an inch above the bottom. These filter/clunk
combinations are manufactured from sintered bronze, have lots of filter area,
and will trap everything and not clog up! Let’s also use one in our tank,
replacing that old clunk that does nothing but lay there. I do not recommend
any in-line filter between the tank and the carb. Thinking about
tanks brings up another frequently asked question: “Will my four stroke run INVERTED?” Of course it will – it doesn’t know
the difference in flight, does it? The potential problems of inverted
operation are two-fold. First off, be careful of your tank location; you must
lower it somewhat to insure the center of the tank is slightly below the center
of the carb. Most importantly, you must slowly turn the engine over by hand
just before starting to insure that you don’t have a hydraulic lock. A good
practice is to turn the model over for starting. Some engines don’t like
extended idle time inverted; in this case, add on-board ignition. Muffler
pressure? Some say yes, some say no. I ALWAYS use it (except for the
YS & OS pumpers, of course). For one thing, it
does help by keeping a steady head pressure on the fuel in the tank.
Additionally, it keeps things in good order as far as any fuel vent spills. I
use a three-line system – one from the muffler pressure fitting to the tank –
This pressure line runs to the top front of the tank; overflow will come out
the muffler. Another line runs from
the tank to the carb, and the third from the tank to an external fill/drain
location. I run this line inside the tank to a location near the lower front
corner of the tank. This way when you defuel, you
don’t have to turn the model over, Terminate this line with a plug, a “Fuel
Dot Fitting,” or as a last resort, a sheet metal screw screwed into the line. Let’s start
this dude by first selecting the correct glow plug. Hey, guys, when all
else fails, read the instructions! For example, always start out with an
O.S. “F” plug in O.S. engines and an Enya #3 in our Enyas.
Saito recommends a “P-3”, but I’ve never been able to find any of those???
The Y.S. manual suggests an O.S. “F” and the Laser manual states that most
any plug will work. Once you have flown using these recommended plugs, you
can experiment with others if you’re having difficulties with a reliable
idle, acceleration, etc. Two alternate plugs are my old standby, the Fox
“Miracle Plug” and for multi-cylinder engines that tend to ‘drop a cylinder’
during the first two hours break-in, a K & B #4520 Long Idle Bar. I have
not yet experimented with the new K & B or Fox plugs Choking the
engine? Surprise! Most of the time, just using a starter for a few seconds
AFTER DETERMINING NO VAPOR LOCK EXISTS will usually draw fuel up from the
tank. If you prefer to choke, pull the engine slowly through two turns with
the throttle wide open, carb venturi covered, and glow plug(s) disconnected.
Be sure to close the throttle and hand-pull the engine through again before
lighting off the plug. An alternative to choking is to simply put your finger
over the muffler outlet while you hand-pull that air pump you normally call a
piston and cylinder through a couple of times. Y.S. engines are different in
that you simply pull them through a few turns to start building tank
pressure, then use your starter. Prop selection:
Please do yourself a big favor and at least start out with the size the
manufacturer recommends. You can fine-tune later. Be sure you balance the
prop. Even some props of my favorite brand – APC – need some minor balancing
now and then. I simply balance by ever so lightly sanding the flashing off
the rear edge of the blades; more off the heavy side. On a related topic, I
always use and recommend Tru-Turn spinners
manufactured by my good friend Bob Obenberger out
at Romco Manufacturing in South Houston Bob@tru-turn.net
I have never had to balance one of his spinners. Another advantage they have
is their deep knurl on the backplate that really
grips those props. Bob can always provide you with the proper adapter kit to
match your engine to the spinner, as well as providing any special cuts you
need to accept any size or brand prop. Let’s set the needle once
and then we can basically forget it! Done correctly, you should not have to
readjust your needle valve unless you change fuel or glow plug brands, change
props, or have a major climate change! DON’T BE A NEEDLE TWEAKER! I guarantee
you will do more harm than good. Ask yourself: Did it run good when you flew
it last? Did it idle OK? Why do you think you have to adjust it now? Be
honest with yourself. Please save yourself many potential engine problems;
Don’t mess with the needle. That said, let’s set it. Before starting, beg,
borrow, or buy a tachometer. That’s correct, you
simply can’t set the needle valve on a four-stroke by ear alone. Oh sure, you
might get lucky once in a while, but why take a chance? Once the engine is
started, let it warm up for a while. Some of our engines are very cold
blooded – my little Enya .53 just won’t take full throttle until it’s had at
least a full minute at part throttle – and this is my most used engine in the
inventory with just under 300 flights dating back to 1992 in the same airplane!
Once the engine is warmed up and your buddy is holding the model, run up to
full throttle. Allow it to stabilize, then while observing the tach, ever so
slowly lean the mixture to the point where the R.P.M. peaks then starts to
sag. Open it up back to that peak reading. Now we’ll richen it just a little
more so that the engine turns somewhere between 300 and 500 R.P.M. LESS than
peak. STOP! This is where we’ll fly. The reduced revs allow for prop
unloading in flight Somewhere along the line,
you’ll goof and either go too lean, load the engine with a bigger prop, or
simply get a backfire – any of these can cause you to knock the prop loose or
actually spin it off. Even with the good Tru-Turn
spinner really biting the prop, sometimes the engine drive hub doesn’t bite
into the spinner backplate. Here’s how we cure
this. We’re going to very carefully drill a 3/32” hole in the hub. We’ll
locate the hole out near the outer edge and drill parallel to the shaft
through the first part of the hub, past the ‘groove’ in the hub, and just a
little into the back part of the hub. Next we’ll cut a piece of 3/32” music
wire just long enough to bottom out in the hub, go through the spinner, plus
1/16” to 3/64th of an inch – just enough to bite into the prop.
Slightly ‘point’ the prop end of the wire. Mark the spinner by rotating it on
the shaft to allow the pin to mark an arc; drill through it slightly
oversize, and check that it mounts without binding. Now use some JB Weld to
secure the music wire into the drive hub. When you next mount a prop, really
lay into it with a good wrench; the pin will bite into the prop. Bet you
won’t ever throw a prop now, Bubba! Well, you have the engine
running, the needle set, and you have flown your batteries out, and it’s time
to go home. After we defuel, restart the engine and
run it dry. Through the breather line (except on the YS), we’ll now add some
after-run oil. Once again, I go with C. F. Lee’s recommendation of Marvel Air
Tool Oil. It’s basically Marvel Mystery Oil with an anti-rusting agent. Some
folks claim they never use after-run oil and never have rusted bearings. To
them I say: “You have been very lucky!” I consider after-run oil cheap
insurance. Incidentally, if you store your engine for an extended period,
Clarence recommends a 50/50 mix of MATO and ATF (Automobile Transmission
Fluid). MATO is available as Marvel Product #080 in 4-oz. cans. The second most
frequent question: Valve checking! Note I didn’t say valve adjusting – which
is something you will seldom, if ever, need to do. All manufactures recommend
checking the valve lash (clearance) after the first hour or two. I agree.
This is when the entire engine is coming together to make itself a well
running machine. I will say that I have only found it necessary to adjust valves
in perhaps only two out of three new engines after this initial break in.
After that, I only pull the rocker covers when either the engine is moved to
a new model or I have real reason to suspect wear – loss of power or
unreliable idle. In other words; “IF IT
AIN’T BROKE, DON’T FIX IT!” As far as the
actual adjusting goes, it’s pretty simple. Just be sure you have the correct
tools and don’t force anything. Turn the engine to T.D.C. (top-dead-center) on
the compression stroke. I checked all of my engine manuals, and everybody
uses two valve clearance numbers as a “go-no-go” measurement, which means the
one thinner feeler gauge should fit quite easily; the larger one shouldn’t.
The “no-go” number is 0.10mm. and is valid for all
major brands. Saito uses 0.03mm; O.S. and Y.S. use 0.04mm; Laser and Enya use
0.05mm as the smaller “go” number. By the way,
although not necessary, while you have the rocker covers off, add some oil
such as Marvel Air tool Oil or other machine oil to the rocker assembly
before replacing the covers. Be careful to not over tighten the cover screws;
they can strip. Ask me how I know L Well, that’s it
gents – Should you have any questions or comments, please feel free to
contact me at either lyslack@juno.com or lyslack@bellsouth.net By the way,
Saito engine manuals are available for download at www.horizonhobby.com Laser instructions are on their web-site. If you need to contact the
manufacturer for service or parts, try: SAITO O.S. P & P Enterprises Hobby Services (972) 423-2282 (217)
398-0007 texasrc@earthlink.net http://www.hobbies.net/ Y.S LASERYS Performance Manufactured
in the (775) 782-4562 ysperf@nanosecond.com ENYAAltech Marketing (732) 225-6144 |