light engine break-in
Posted: Sat Jun 16, 2001 7:12 am
'Back in the 40's, Cubs and Airknockers tied down with their freshly
overhauled engines pointed into the wind, churning out the required 4 hours
of run in at ever increasing rpm to achieve break-in. Some gave good
performance for 600 to 800 hours, and some burned excessive oil whenever
flown. Today, 40 years later, some engines are still being broken in
essentially the same way, ignoring the knowledge science has gained for us
in the meantime. High power microscopes and other measuring devices have
shown that our freshly refinished steel or chrome cylinders with their
mating rings and pistons are not what we think. These smooth, honed, cross
hatched surfaces are, when looked at with these instruments, in reality, as
rough as the Rocky Mountains and look the same ! ! ! Our desired break-in
really consists of wearing off the peaks of these surfaces. Actually these
parts literally weld together and tear apart on each stroke! Needless to
say, this gener- ates a vast amount of heat. Too much heat and pistons get
scuffed, cylinders score and rings lose their tension. The engine consumes
oil and generally performs poorly. I know of more than one engine which had
to be topped because of this situation. Since we know that excessive heat is
the problem, a simple procedure will virtually assure a good break-in. I've
used this with excellent results on a variety of air cooled engines. What I
do is prevent overheating by limiting the running times. The initial run is
preceded by removing one spark plug from each cylinder, then turn the engine
over with the starter and watch for oil pressure to build up to
approximately 20 PSI. Use straight mineral oil and in cold weather preheat
the oil and the engine to 80 degrees F. Install the spark plugs, place the
aircraft pointed into the wind, have an assistant stand by outside the
aircraft to watch for oil leaks, keep people from walking into the
propeller, and check the cylinder tempera- tures by feel. Start and run the
engine under 1 000 RPM until the cylinder barrel fins (not heads) get too
hot to keep your hand on. Be sure to monitor the oil pressure and cylinder
head temperature on each run. Then shut down, and let the engine cool down
to ambient temperature. This usually takes between 20 and 30 seconds of run
time. The subsequent runs usually are about double the preceding time before
the fins get too hot and you must shut down, i.e., the second run will be 40
to 60 seconds, the third run will be close to two minutes, 3rd run etc. I
record these times and temperature readings at the start, during, and at the
end of the runs. Maximum Cylinder Head Temp. of 500 degrees F. for most
engines. Check the engine operating manual for your particular engine.
G@adLally increase the RPM and the run times until the total run time is 1/2
hours. Then try a brief, not over 15 seconds at full power RPM run. DO NOT
CYCLE A CONTROLLABLE PROP. If you were to cycle the prop at this time from
low to high pitch, scuffing of the pistons and scoring of the cylinder walls
could easily occur. You would be "lugging" the engine, increasing the side
load on the pis- tons while a high friction coefficient is present. If your
engine is equipped with counterweights, cycling the prop may cause the
crankshaft to detune, and on some engines the pins may break. Make any
ground adjustments during cool down periods and check on the next run time.
When your RPM has reached 1600 to 1800, make a quick mag check on one of the
last run times prior to flight. Now it's ready to fly. Keep the aircraft
light (minimum fuel, no baggage, passengers, etc.) Push or tow the plane to
the takeoff point since the taxiing can easily overheat and ruin the engine
! ! ! Use minimum power to get some airspeed (and cooling airflow) before
applying enough power to achieve a flat and clean climb out to a minimum
cruise altitude. Use minimum RPM to achieve level flight for good cooling.
Do not move the propeller pitch from low to high pitch setting. Light Plane
Engines Break-in Period Fly with the propeller in low pitch for the first
5-10 minutes after takeoff with the engine running relatively free of
lugging loads. The high RPM also supplies the cylinders and pistons with the
maximum amount of oil. After 5-1 0 minutes, set the propeller to the desired
setting. Fly for 30 minutes at maximum cruise power settings for your
aircraft. (Note any engine malfunctions and monitor and record all temper-
ature readings.) It is good to have a CHT temp. probe and readout on each
cylinder if possible. In about 1/2 hour, the CHT should decrease
approximately 50 to 75 degrees, show- ing that initial break-in has been
achieved. Keep the engine working at all times, but do not lug and avoid
abrupt fluctua- tions. After you have landed, check the oil and determine
the consumption. Repeat the flight as outlined above for another 30 minutes,
again measure the oil consumption. If the con- sumption is excessive, fly
the airplane for 45 minutes at full rated allowable power. Note: all flight
procedures are subject to proper pilotage, terrain and obstructions. If high
oil con- sumption continues, check the compression for proper ring
sea*irt.g, it is possible to have to remove and degla7e the cylinders again,
and start over with the break-in procedures. However, if the above
directions are followed this is very unlikely. r For the next 10 hours,
operate the aircraft with light loads and power settings. Avoid sudden power
reductions which can cause cooling cracks. During descent, plan ahead and
start descending further out and keep the RPM and cylinder head temp. up and
maintain manifold pressure at all times to show that the engine is working,
but do not lug. Check the oil screens or filter at the end of the first hour
or two for metal particles. It is normal for some small metal particles to
show up in either the screens or filter. Check these particles with a magnet
to see it any particles are steel. The oil filter should be opened up and
the filter element spread out to thoroughly check the interior of the pleats
for metal particles. This procedure should be accomplished again at about 10
to 15 hours of run time on the engine. If oil consumption has stopped a
detergent type aircraft oil can now be put in the engine after IO to 15
hours operating time. Steel cylinders do not glaze as easily as chrome
cylinders therefore, it is very important not to allow chrome cylinders to
glaze over by running at low RPM'S. If glazing occurs, high oil consumption
can be expected during the life of the engine unless the cylinders are
removed and deglazed. After five or six hours, the pistons will have been
sufficiently burnished to prevent their scuff ing and cylinder walls
scoring. Cycling the prop should no longer be of concern, but when you do
cycle the prop on a ground run, run up to 1700 RPM in low pitch, then check
the prop operation by moving the pitch to high just long enough for the RPM
to drop to about 1500. This will eliminate unnecessary lugging of the
engine. Maximum oil consumptions are listed for the following en- gines
during run in: For 0-235's it is .9 pounds per hour or .56 quarts per hour.
For 0-290's, it is 1 pound per hour or .56 quarts per hour. For 0-320's it
is 1.2 pounds per hour or .67 quarts per hour. For 0-360's, it is 1.4 pounds
per hour or.78 quarts per hour. These are the maximum oil consump- tion
stats for a new or overhauled engine. If it is over this, you should check
very carefully and possibly consider engine teardown. I recommend that a
newly built aircraft should not use a new or freshly overhauled engine for
ground taxi tests as this can be very detrimental to proper break-in
procedures due to lack of cooling.'
overhauled engines pointed into the wind, churning out the required 4 hours
of run in at ever increasing rpm to achieve break-in. Some gave good
performance for 600 to 800 hours, and some burned excessive oil whenever
flown. Today, 40 years later, some engines are still being broken in
essentially the same way, ignoring the knowledge science has gained for us
in the meantime. High power microscopes and other measuring devices have
shown that our freshly refinished steel or chrome cylinders with their
mating rings and pistons are not what we think. These smooth, honed, cross
hatched surfaces are, when looked at with these instruments, in reality, as
rough as the Rocky Mountains and look the same ! ! ! Our desired break-in
really consists of wearing off the peaks of these surfaces. Actually these
parts literally weld together and tear apart on each stroke! Needless to
say, this gener- ates a vast amount of heat. Too much heat and pistons get
scuffed, cylinders score and rings lose their tension. The engine consumes
oil and generally performs poorly. I know of more than one engine which had
to be topped because of this situation. Since we know that excessive heat is
the problem, a simple procedure will virtually assure a good break-in. I've
used this with excellent results on a variety of air cooled engines. What I
do is prevent overheating by limiting the running times. The initial run is
preceded by removing one spark plug from each cylinder, then turn the engine
over with the starter and watch for oil pressure to build up to
approximately 20 PSI. Use straight mineral oil and in cold weather preheat
the oil and the engine to 80 degrees F. Install the spark plugs, place the
aircraft pointed into the wind, have an assistant stand by outside the
aircraft to watch for oil leaks, keep people from walking into the
propeller, and check the cylinder tempera- tures by feel. Start and run the
engine under 1 000 RPM until the cylinder barrel fins (not heads) get too
hot to keep your hand on. Be sure to monitor the oil pressure and cylinder
head temperature on each run. Then shut down, and let the engine cool down
to ambient temperature. This usually takes between 20 and 30 seconds of run
time. The subsequent runs usually are about double the preceding time before
the fins get too hot and you must shut down, i.e., the second run will be 40
to 60 seconds, the third run will be close to two minutes, 3rd run etc. I
record these times and temperature readings at the start, during, and at the
end of the runs. Maximum Cylinder Head Temp. of 500 degrees F. for most
engines. Check the engine operating manual for your particular engine.
G@adLally increase the RPM and the run times until the total run time is 1/2
hours. Then try a brief, not over 15 seconds at full power RPM run. DO NOT
CYCLE A CONTROLLABLE PROP. If you were to cycle the prop at this time from
low to high pitch, scuffing of the pistons and scoring of the cylinder walls
could easily occur. You would be "lugging" the engine, increasing the side
load on the pis- tons while a high friction coefficient is present. If your
engine is equipped with counterweights, cycling the prop may cause the
crankshaft to detune, and on some engines the pins may break. Make any
ground adjustments during cool down periods and check on the next run time.
When your RPM has reached 1600 to 1800, make a quick mag check on one of the
last run times prior to flight. Now it's ready to fly. Keep the aircraft
light (minimum fuel, no baggage, passengers, etc.) Push or tow the plane to
the takeoff point since the taxiing can easily overheat and ruin the engine
! ! ! Use minimum power to get some airspeed (and cooling airflow) before
applying enough power to achieve a flat and clean climb out to a minimum
cruise altitude. Use minimum RPM to achieve level flight for good cooling.
Do not move the propeller pitch from low to high pitch setting. Light Plane
Engines Break-in Period Fly with the propeller in low pitch for the first
5-10 minutes after takeoff with the engine running relatively free of
lugging loads. The high RPM also supplies the cylinders and pistons with the
maximum amount of oil. After 5-1 0 minutes, set the propeller to the desired
setting. Fly for 30 minutes at maximum cruise power settings for your
aircraft. (Note any engine malfunctions and monitor and record all temper-
ature readings.) It is good to have a CHT temp. probe and readout on each
cylinder if possible. In about 1/2 hour, the CHT should decrease
approximately 50 to 75 degrees, show- ing that initial break-in has been
achieved. Keep the engine working at all times, but do not lug and avoid
abrupt fluctua- tions. After you have landed, check the oil and determine
the consumption. Repeat the flight as outlined above for another 30 minutes,
again measure the oil consumption. If the con- sumption is excessive, fly
the airplane for 45 minutes at full rated allowable power. Note: all flight
procedures are subject to proper pilotage, terrain and obstructions. If high
oil con- sumption continues, check the compression for proper ring
sea*irt.g, it is possible to have to remove and degla7e the cylinders again,
and start over with the break-in procedures. However, if the above
directions are followed this is very unlikely. r For the next 10 hours,
operate the aircraft with light loads and power settings. Avoid sudden power
reductions which can cause cooling cracks. During descent, plan ahead and
start descending further out and keep the RPM and cylinder head temp. up and
maintain manifold pressure at all times to show that the engine is working,
but do not lug. Check the oil screens or filter at the end of the first hour
or two for metal particles. It is normal for some small metal particles to
show up in either the screens or filter. Check these particles with a magnet
to see it any particles are steel. The oil filter should be opened up and
the filter element spread out to thoroughly check the interior of the pleats
for metal particles. This procedure should be accomplished again at about 10
to 15 hours of run time on the engine. If oil consumption has stopped a
detergent type aircraft oil can now be put in the engine after IO to 15
hours operating time. Steel cylinders do not glaze as easily as chrome
cylinders therefore, it is very important not to allow chrome cylinders to
glaze over by running at low RPM'S. If glazing occurs, high oil consumption
can be expected during the life of the engine unless the cylinders are
removed and deglazed. After five or six hours, the pistons will have been
sufficiently burnished to prevent their scuff ing and cylinder walls
scoring. Cycling the prop should no longer be of concern, but when you do
cycle the prop on a ground run, run up to 1700 RPM in low pitch, then check
the prop operation by moving the pitch to high just long enough for the RPM
to drop to about 1500. This will eliminate unnecessary lugging of the
engine. Maximum oil consumptions are listed for the following en- gines
during run in: For 0-235's it is .9 pounds per hour or .56 quarts per hour.
For 0-290's, it is 1 pound per hour or .56 quarts per hour. For 0-320's it
is 1.2 pounds per hour or .67 quarts per hour. For 0-360's, it is 1.4 pounds
per hour or.78 quarts per hour. These are the maximum oil consump- tion
stats for a new or overhauled engine. If it is over this, you should check
very carefully and possibly consider engine teardown. I recommend that a
newly built aircraft should not use a new or freshly overhauled engine for
ground taxi tests as this can be very detrimental to proper break-in
procedures due to lack of cooling.'