If I’ve Said It Before, I’ll Say It Again.
There is always more then one way to skin a cat. If you find a different way or your instructor
wants to do things differently, by all means try it. Knowing many different ways to do the same thing is great. Then you can
use whatever methods works best for you.
Know Your Motors Parts. If you are familiar with the different
parts of a glow motor then continue on below. If not, head to Basic Motor Parts before continuing.
Heat is a killer of R/C motors When your adjusting your motor for full
speed keep this in mind. Adding a few clicks past a certain point, can and will at the very least decrease your motors life
span. At the worst it can ruin your brand new engine on it’s first flight.
Leaning The Motor.
Turning the high speed needle in (where it
goes further in to the carburetor) restricts the amount of fuel going to the carburetor. This changes the air to fuel mixture
and is know as leaning the motor. Less fuel and a higher percentage of air gives more power, but raises the amount of heat
that the motor will generate. The fins of the motor case help to dissipate heat, but so dose the lubricants in the fuel. Glow
fuel has a certain percentage of caster or synthetic oil mixed in, usually 16 to 20%. Some even use a caster/synthetic oil
blend. The important thing to remember is if you restrict the amount of fuel you also restrict the amount of oil going to
the motor. This oil besides keeping parts lubricated, carries off heat from the motor helping it to stay within normal operating
Richening The Motor. Turning or screwing out the high speed needle valve
will richen the motor. This decreases power, but the motor will run cooler. This will, with very few exceptions, prolong the
life of your motor. One exception might be on a specially designed ABC type motor made to run at a higher operating temperature.
Without the extra heat the motor head will not expand to the proper size. This causes the piston to actually wear faster or
in the wrong way and you’ll lose proper compression and power.
So turning in the high speed needle equals lean. Turning it out equals rich. This is
very important to understand, so read it again if need be.
Test Stands. Breaking the motor in on a test stand is very important.
I will relent here and admit that I’ve broken in a motor both ways. In a test stand and on a plane. But now that I have
more experience, I can honestly say that breaking using a test stand is the way to go. Why you might ask? Well, for several
reasons. With the motor on a test stand there is no way to subcome to the temptation of doing a 5minute break-in and then
flying the plane. Having the motor setup and broken-in will go a long way to making your flying session much more enjoyable.
On a test stand you can control the break-in procedure and not have to fight with a plane that wants to mover forward or be
turned over by a wind guest. Also with the motor in a test stand you won’t have to worry about dirt particles being
sucked off the ground and in to the carburetor intake. After all this is a very critical time of your motors life.
Bench Vise. Never clamp your motor in a bench vise to break it in. this
does not allow the motor any leeway to vibrate and can wear or break the piston connecting rod. Take a board about 12 inches
long and make a cut out on one end that will fit the size of your motors engine lugs. Mount your motor to the stand and install
a fuel tank behind the motor. For throttle control simple screw a servo arm to the board. Tighten or loosen the screw till
it has just enough tension to hold it’s position while the motor runs. Attach a connecting rod from the servo arm to
the throttle arm of the motor. Use a clamp to hold the test stand to a work bench or picnic table. Let about 6 inches of the
test stand to hang over the table. This will allow it to vibrate a little.
Use a fuel from 0 to 15% nitro. 10% is a good
starting point. The motor will run cooler and you can always move up to a higher nitro content fuel after break-in. I personally
never use a fuel higher then 15%. Not saying that you shouldn’t, but keep one thing in mind. Using a higher nitro content
fuel like 25 to 35% (usually used for racing) will cause the piston and sleeve to ware under a higher temperature. With this
type of wear pattern you must continue to use higher priced, higher content fuel. If you use a lower nito fuel latter on.
The motor will not run well.
Prop Selection. Use the right size prop. A propeller that is to
large will cause excessive heat and an improper wear between the piston and the sleeve. Some say use the smallest prop made
for the motor as specified in the owners manual, this is misinformation which I’ll explain soon. I use the prop that
I intend to use most often with the motor. I have had great luck with this, but I also understand more about motors then someone
new to the hobby.
Here is what the smaller prop suggestion is all about
You don’t use a smaller prop, but actually a prop cut down. For instance, a .40 sized motor is one of the most popular
size motors used in trainers and sport planes. A .40 size regularly uses a 10 x 6 size prop. The reason why someone uses a
smaller prop is to keep the motor rpm up while still maintaining a 4 cycle. This allows a higher rpm (closer matched rpm speed
if you will) to what the motor will be doing during regular after break-in use. yet it still keeps the motor running cooler
due to less load and more fuel lubricants caring the heat away. Here is where the misinformation comes in. On a .40 sized
motor you’d use a 8 x 6 prop. The 8 x 6 prop was made for a .20 size engine and has a smaller diameter hole in the center
(called the prop hub) to fit the smaller size motor shaft. You would need to reem or drill out the prop hub to fit the larger
motor. This weakens the prop hub and can cause the prop to break throwing a blade. No need to explain why this isn’t
safe. What was meant by using a smaller prop is this. You take a take a 10 x 6 prop and cut 1inch off each side to make a
8 x 6 prop with a full size hub.
I now use the size prop I’m
going to use most with my motor. Here is why. Most of the engines used today are of the ABC type. ABC motors need the extra
heat to break in properly. Some ABC motors like the Tiger Shark will be ruined if it is allowed to 4 stroke during break-in.
Some motors like the O.S. 40 FP are made using basically the same methods from the day they were first introduced. They can
be broken in using the method decried above. Some newer ringed motors can’t be broken in using this method or engine
life will be reduced. Also, I use 15% Nitro fuels for both break-in and flying. I also use an engine break-in test stand.
This is again proof of why you need to follow the exact break-in procedures from the owners manual for that motor. Follow
the link below to find the manual for your motor if you don't have one.