Engine Break-In Tips
A good guide Breaking in your R/C Engine...
This is a great guide for the correct
break-in basics of R/C engines. Follow these guidelines to hopefully have a long and healthy
R/C Engine Life!
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Breaking in your Engine
Original publication by Norman Osborne
Adapted to current views by Pé Reivers
Standard fuel blends are:
Glow fuel: 72% methanol 10% nitro 18% oil (castor or synthetic) Glow fuel for break-in: 80% methanol 20% oil (castor or synthetic)
The object of running in an engine, is to get
the engine to the point where all the rubbing surfaces are perfectly
mated to each other at all temperatures likely to be attained, while
causing as little wear to the engine as possible in the process. The
benefits of doing this properly are twofold; the engine would be a
'better' engine throughout it's life, and that life would also be
extended. A good tip is to use an old glowplug when first running in an
engine, as often minute pieces of metal from the running in process or
swarf left from manufacturing can destroy a glowplug in seconds.
The method used to achieve this is simple. Run
the engine very rich and lightly loaded at first and gradually increase
the amount of work the engine is allowed to do, at the same time
gradually increasing the temperature that the engine is allowed to
attain, by judicious use of the main needle valve. This gradual process
is spread over approximately the first half hour of the engine's life
when it should be ready for its first full speed run. During all running
of new engines, the setting should be on the rich side of peak power.
All running-in during the first tankfuls is done with the throttle fully open.
Ringed Engines
Start by using one of the smaller propellers
recommended by the manufacturer and a minimum of 20% of oil in the
straight or low nitro fuel. When using synthetic oil, addition of castor
for the first run(s) is recommended by most manufacturers and engine
authorities.
Run the first tankful absolutely soggy-rich,
keeping the glow-plug lead attached if necessary to keep the engine
running. Keep all runs of short duration of one-half to one minute, with
a few minutes cooling down time between each. The number of heat cycles
makes the metal "set" and speeds up the final fit of the components.
The rich mixture and the short runs prevent the temperature from rising
too much. Debris that forms will be washed away by the excess fuel and
oil.
For the next few runs set the main fuel needle
to give a very fast four-stroke with just the occasional hint of
two-stroking. Allow engine to run for 30 seconds and then stop for a two
minute cooling period, Start again for 30 seconds then allow to cool
again. Gradually increase the length of the full throttle runs, unless
the engine shows a tendency to bind, which can be heard by the labouring
sound and unwillingness to maintain a steady rpm. At the end of two
tankfuls lean the engine out to the point where the engine is on the
verge of two-stroking and four-stroking and go fly, reducing throttle
from time to time to allow the engine to cool a bit. Keep this up for
about four litres of fuel. By now the engine should be steady running,
without any tendency to sag, and can be leaned further to the point,
that max. power is achieved. Always back off the needle a bit until a
clear drop in rev's can be noticed. That is the standard flight setting
for longevity and strong running in the air. During flight, the engine
will lean out a bit, so you will be on the safe side of disaster with
this setting.
If the engine is to be used under more harsh
conditions (e.g. with a tuned pipe or high nitro fuel), then it will
need some extra running-in under the short-run procedure, using the
same fuel as for it's intended use, but with extra oil added. 25% oil is
not too much for the first runs of a racing engine and will do it a lot
of good.
All this might seem a long-winded process but
it is necessary to get the best surface finish with the least wear
inside your precious engine.
The reason for everything being done in small
and gradual steps is that the rubbing surfaces have to be mated at
gradually increasing pressures and to further complicate this the shape
of the parts change as temperatures are increased. As an illustration,
the cylinder and piston are round and parallel sided when made. As the
engine warms up the top half of the cylinder gets hotter than the bottom
half and so expands unevenly, worse than this the exhaust side of the
liner runs hotter than the transfer side, then to add to the problem the
front of the engine (in the airstream) runs cooler than the rear of the
engine, so you can see the liner would be anything but perfectly round
and parallel when thoroughly hot. That is the reason, that a well run-in
engine has a bit less compression during starting than a new engine.
The piston and ring are subject to similar
stresses. The ring alters its length depending on temperature and is
also going up and down a bore which is no longer round or parallel sided
and is guided through this operation by a piston which gets hotter at
its head where it is in contact with the burning fuel mixture and
therefore the diameter of the head is bigger than the walls. The exhaust
side of the piston is hotter than the transfer side so the piston is no
longer round or, as mentioned earlier, parallel sided either. All these
distortions are larger or smaller depending on the temperature of the
engine, so the running-in process has to allow the engine to make the
mating working surfaces suitable for all these varying conditions.
During the run-in check all screws and bolts
for security and if you have to tighten any cylinder head bolts,
remember to tighten a little at a time and in diagonal rotation. You
might also find the glow-plug has been affected by small metal particles
fired at it during running-in. If you have any doubts change it and
keep the old one only for running-in only, or throw it away. It did
serve it's duty.
Running in ABC engines
An 'ABC' engine is one with special liner and
piston metallurgy, e.g., the piston is aluminium (A), the liner is brass
(B), and the brass is chrome plated (C). Generally these are
performance orientated engines.
When an ABC engine is warmed up, the top of
the liner, which made of brass, will expand more than the piston which
is made of aluminium. Consequently, as the engine reaches working
temperature the piston seal would not be very satisfactory. The
manufacturers have taken steps to counteract this undesirable state of
affairs by making the liner and piston the correct sizes for when the
engine is hot. This means that when cold the piston is a very tight fit
at the top of the liner, to the point where some make a light groaning
noise when forced over Top Dead Centre (when the piston is at the very
top of its travel, or TDC for short). Warning: a new ABC engine
should never be turned over slowly, especially when still lubricated by
the original preserving oil that the engine is shipped with. That will
cause slight, but immediate damage to the top part of the piston fit,
because the surfaces are still rough.
Little running-in is required with these
engines, as the cylinder temperature must be raised to full working
temperature as quickly as possible to avoid excessive piston wear due to
the very tight fit at lower temperatures. As a matter of fact, it is
best to fly these engines out of the box, using a rich setting with
occasional four stroking. It is important to use an extra 5% of oil on
top of the normal mixture.
When bench running, my usual method is to use
about 5% extra castor oil in the fuel and set the engine for just below
full speed running (throttle fully open, main needle just a little bit
rich), and run the engine in short cycles of approximately 30 sec's.
full speed and 5 sec's. at 1/3 speed, for the first 15 minutes. This
keeps the cylinder temperature up and the slow running should give time
for any hot spots to cool down somewhat. For the next 45 minutes use the
engine normally but keep it just a touch rich (just 2 or 3 clicks).
After that, normal fuel can be used as per manufacturers
recommendations.
Setting the main needle
This is a most important setting as not only
does it set maximum power but it also controls the running temperature
of the engine and from there the length of the engine's life, the life
of the glow-plug and the overall reliability of the engine's running in
flight or elsewhere. Engines don't very often cut out in flight because
they are set slightly too rich, but they most certainly do when set too
lean.
It takes about five minutes to learn the drill
for correct needle valve setting so it's worth taking the trouble for
the long term benefits gained.
The drill is to start the engine on low
throttle, for safety and usually easier starting due to higher gas
speeds through the venturi and consequent better atomization of the fuel
droplets. Once started, open the throttle fully and set engine to just
four-stroking rich. Leave the engine to warm through thoroughly at top
speed for a few moments, then adjust the needle until the engine is just
off four stroking and running smooth. At this point, further leaning of
the mixture results in RPM increase. From this established point richen
up slowly again until a small but definite drop in RPM is noticed, with
the engine still two-stroking. Lift the nose of the model up vertically
and if the small loss of RPM is regained then you should have a good
flight setting. If the model has a tendency to go rich or go lean in
flight then an extra allowance will have to be made for this on the
final setting.
The aim of this is to give maximum power from
the engine when it is needed most, either when the model is climbing or
when turning sharply and will also give sweet and cool running during
level flight, the best of both worlds.
What happens when an engine is set too lean
The glow-plug engine keeps running because the
heat of compression and the catalytic action of the glowing plug
material with the methanol mixture ignite the charge in the cylinder at
the correct moment. This catalytic action also keeps the plug lit.
Sometimes an engine will start without adding glow to the plug after it
has been stopped for several minutes. A little thought will let you see
that the whole system is very temperature dependent. No spark to set it
off, no injection of fuel to set it off. Just the combination of these
two properties.
When an engine is set lean i.e., for maximum
RPM at the start of a tankful of fuel, anything which slows the passage
of the fuel through the needle valve will make the engine run over lean.
Some engines will not continue to run in this condition and so cut dead
but the majority will continue to run to some degree.
As the tankful of fuel gets used the fuel
pressure, as seen by the needle valve, gradually reduces and as a result
the engine gets a progressively leaner mixture as the flight continues.
As the engine started set in a lean condition it must progress into the
over lean condition and maybe go so far as to cut out, suffer from
overheating and get damaged.
When the engine runs flat out, ignition timing
and engine temperature should be as the designer intended but as the
mixture gets into the over lean area temperatures will start to rise.
This is due to lack of extra internal evaporation of excess fuel, and
hotter burning of lean mixtures. Over-lean mixtures can change
combustion characteristics in a way that imparts more heat to the
surrounding engine structure leaving less for useful work. The fit of
the moving parts becomes worse, and friction rises.
As a result of this the incoming charge is
heated a little more than it should be and when compressed is at a
higher temperature than it otherwise would be. The secondary effect of
the engine structure being at a little higher temperature is that the
glow-plug element is also a little hotter, which advances the onset of
ignition.
As already explained, ignition timing is
controlled by the temperature of the compressed fuel/air mixture
combined with the temperature of the glow-plug element. The net result
of both of these being raised is early ignition in the next cycle.. This
early ignition gives just a little more time for even more heat to be
transferred to the engine structure before the hot gasses are exhausted
from the engine and so jacking up engine temperatures just a little
more, resulting in the next cycle jacking up temperatures yet again.
This is the slow build situation that causes
engine seizure in some cases and in other cases runaway early ignition
that makes an engine stop quickly in the air and even throw the prop, as
though it has seized, but in fact feels perfectly O.K. and runs O.K.
when it has cooled down again.
Many of the modern engines do not reach these
extremes but keep running at a steadier but much higher temperature than
they were ever designed for. These engines run other risks which are
much less obvious.
One risk common to ail engines which are run
at elevated temperatures is that the oil gets very hot, thins out too
far and so can no longer lubricate as effectively as it should,
resulting in excess wear and shortened engine life. Synthetic oil will
evaporate at very high temperatures without leaving a trace of
lubrication.
The less obvious damage that can occur is not
usually laid at the door of a lean fuel setting but I believe much of
the time it is a relevant factor. When the engine has overheated and
reached the point of too early ignition the burning mixture expands the
gasses well before top dead center and so the pressures inside the
cylinder are much higher than they should be. These extra high pressures
at the wrong time in the combustion stroke try to force the piston down
with greater power than the designer intended and therefore overload
the wrist pin in the piston and the little end bearing, the con-rod is
more highly stressed, the big end bearings and the main bearings on the
crankshaft are also subjected to higher loads. In four stroke engines
it is not uncommon that the engine will knock and even kick back and
throw the prop. Knocking can be heard, and is a typical sound like tin
foil being rubbed.
These extra stresses may only result in wear
being more rapid than necessary but if it is a regular occurrence it can
result in very early bearing failure, and if it happens to be the
con-rod that gives up first the resultant damage can be very expensive.
With all this in mind, when adjusting the main needle of your engine the catch phrase should be 'The future of your engine is in your hands'.
Setting the low speed
The need for a low speed adjustment on the
carburetor is because as the throttle is closed it lets less air
through into the engine and to keep the fuel air mixture within
combustible limits the fuel flow. has to be altered, it's too fussy to
leave to chance.
Most manufacturers have opted for a two needle configuration or something which works in a similar manner.
To adjust this low speed mixture start the
engine, warm it up and make sure the main needle is properly set.
Connect the glow-plug lead to energize the plug and slow engine down by
gradually closing the throttle until the engine starts to run badly. At
this point adjust the slow run needle to give smoothest running
characteristics just a little on the rich side of fastest setting.
Having made this adjustment slow the engine further until it runs badly
again, now adjust slow needle until engine runs smoothly once more and
continue this step by step procedure until the desired tickover has been
reached, with the throttle barrel barely 1mm open. Now remove the plug
lead and repeat the whole process. If the engine cuts dead in the middle
of adjustments it's usually because it is too lean.
Having reached a slow tick over we have to
check if the engine will pick up properly. Open the throttle to full
speed with a smooth sweep, without jamming the controls. I know of many
people who demand their engine to respond well to slamming the throttle
open, but in two-stroke engines, this is asking for trouble and not to
be recommended. If the engine picks up but splutters a little whilst
doing so, the low speed needle is a little on the rich side. If the
engine appears to miss and then picks up suddenly the low speed needle
is slightly lean, and if the engine cuts dead when the throttle is
opened richen the low speed needle 1/4 turn and try again, adjusting in
small increments.
If the engine starts to pick up pretty well
and then cuts at about 1/3 speed or so, try opening the main needle two
or three clicks.
On many engines there has to be a compromise
or two to get the low speed, midrange, top speed and pickup to a
useable whole, and usually the compromise is that somewhere in the range
the carburettor has to be set a little richer than would be considered
ideal. Rich mixtures are an assurance for longevity and seldom cause the
engine to stop, unless extreme.
Four-Stroke engines
The previous sections are written specifically
for two-strokes, but exactly the same principles apply to a
four-stroke, just some of the symptoms are slightly different.
When running-in from new use a fuel with 20%
oil of which at least half is castor oil for the first runs. A
four-stroke cannot be made to four-stroke when rich, it's already doing
it, but what does happen is the engine misfires in a rather uneven
manner, the richer the setting the more pronounced the misfire. The main
needle, after running in, is set in exactly the same manner i.e., just
on the slightly rich side of maximum RPM., when the engine is thoroughly
hot. The use of a rev. meter is invaluable here, because adjustment by
ear is more difficult than in two-strokes.
If the main needle is set too lean the engine
may slow down with the. exhaust exhibiting a more leaden note than usual
and may progress to the point where the engine stops with a bang due to
'detonation' and throws the propeller off in flight, or on the ground
and perhaps at whoever is standing in the way.
'Detonation' is like early ignition but the
difference is that instead of the mixture burning progressively from the
glow-plug outwards, the temperature and pressure in the cylinder are
such that the whole fuel charge ignites at the same time, before TDC,
stops the piston dead, and blows it back the other way.
'Knocking' or 'Pinking' are like a slightly
milder form of detonation that happens late enough in the compression
stroke for the flywheel effect of the propeller to get the piston over
TDC and therefore for the engine to keep running. Always close the
throttle and open the main needle a bit more when this happens as it
over stresses, and may damage the engine.
The main defense against these phenomena is to
run the engine a little richer, and mix in some acetone (1% - 3%) in
the fuel to stabilize combustion. Adding some 2% of water to the fuel
may also suppress Knocking. (in hot, humid weather). This works in two
distinct ways, first the richer mixture will keep the engine a little
cooler, thus making the conditions for commencement of 'knocking' harder
to attain and secondly and very importantly, a rich mixture is much
less prone to detonation than a lean mixture. These two effects work
together, either for you or against you depending whether you set the
main needle rich or lean. Again, the engine's fate is in your hands.
The low speed needle is adjusted in the same
manner as a two-stroke except generally speaking it needs to be
noticeably richer than a two-stroke, to ensure a good pick-up when the
throttle is opened and also on some engines to stop 'knocking', and the
consequent risk of throwing the propeller, whilst the engine is picking
up speed. In general, speed pick-up from idle is far more better in
four-strokes than that in two-strokes
A Few General Do's and Don'ts
Good Engine Break-in Procedure
Adapted from Ed Moorman
Pre-lube the engine with some after run oil.
Make sure the oil content in the fuel is 18% or more. 20% is better for
break in. Castor oil or a castor oil/synthetic blend offers the most
protection as synthetic oil burns off during a too lean run and offers
no protection. I won't use a 100% synthetic oil fuel as all engines will
always lean out in flight, and I want the added protection of castor
oil.
Start the engine, let it run rich and at
slow speed, not necessarily an idle, until the cylinder fins are warm,
then go to full throttle, quickly lean it out to slightly richer than
MAX RPM. After 5 seconds, pull the fuel line off or pinch it to kill the
engine quickly, so that it doesn't linger at a too lean mixture. Let
the engine sit until it is relatively cool to the touch. (The heat/cool
cycle)
Now, do it again, but let it scream at full throttle for 10 seconds, kill it the same way and let cool. Another heat/cool cycle.
Increase the hot run by 5 seconds each run until you have a 30 second hot run.
Then do (5) 30 second hot runs. Now it's
essentially broken in, so NOW adjust the idle mixture and you're ready
to fly. I usually run a tank through at this point at various throttle
settings, while I'm adjusting the idle mixture.
NEVER go to full throttle after any engine start until the head is warm to the touch.
O.S. Engine Break-in Procedure
Taken from O.S. .46 FX manual
All internal-combustion engines benefit from
extra care when they are run for the first few times known as running-in
or breaking-in.
This allows the working parts to mate together under load at operating temperature. Therefore, it is vitally important to complete the break-in before allowing the engine to run continuously at high speed and before finalizing carburetor adjustments. However, because O.S. engines are produced with the aid of the finest modern precision machinery and from the best and most suitable materials, only a short and simple running-in procedure is called for and can be carried out with the engine installed in the model. The process is as follows.
1. Install the engine with the propeller
intended for your model. Open the needle-valve to the advised starting
setting and start the engine. If the engine stops when the glow plug
battery disconnected, open the needle-valve to the point where the
engine does not stop. Run the engine for one minute with the throttle
fully open, but with the needle-valve adjusted for rich, slow
"four-cycle" operation.
2. Now close the needle-valve until the
engine speeds up to "two-cycle" operation and allow it to run for about
10 seconds, then reopen the needle-valve to bring the engine back to
"four-cycle" operation and run it for another 10 seconds. Repeat this
procedure until the fuel tank is empty.
3. Re-start and adjust the needle-valve so
that the engine just breaks into "two-cycle" from "four-cycle"
operation, then make three or four flights, avoiding successive
"nose-up" flights.
4. During subsequent flights, the
needle-valve can be gradually closed to give more power. However, if the
engine shows signs of running too lean, the next flight should be set
rich. After a total of ten to fifteen flights, the engine should run
continuously, on its optimum needle-valve setting, without loss of power
as it warms up.
5. After the completion of the running-in adjust the carburetor at optimum setting.
Optimum needle setting(1)
Slowly advance the throttle to its fully open
position, then gradually close the needle-valve until the exhaust note
begins to change. (4-cycle to 2-cycle) At this point, disconnect the
battery from the glow plug, taking care that the battery leads or
glow plug clip do not come into contact with the rotating propeller. If
the engine stops when the battery is disconnected, close the
needle-valve about 30° and restart.
Optimum needle setting(2)
As the needle-valve is closed slowly and
gradually, the engine rpm will increase and a continuous high pitched
exhaust note, only, will be heard. Close the needle-valve 10-15° and
wait for the change of rpm After the engine rpm increases turn the
needle-valve another 10-15° and wait for the next change of rpm. As the
speed of the engine does not instantly change with needle-valve
readjustment, small movements, with pauses between, are necessary to
arrive at the optimum setting.
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