piston damage causes 2
TRANSCRIPT
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This piston is NORMAL in appearance.The deposits on the piston dome are fromthe oil and ash, fuel contaminants and
unburned carbon. As the thickness increases
with operating time, the color gets brighter
because of higher surface temperatures.Depending on gasoline and oil used, normal
deposits may also be brown, from light tan
colour to almost black dark brown.Heavy black deposits on the piston dome are
unburned carbon accumulated because of
too low temperatures resulting from light
load operation or too rich a mixture.Brown or black varnish on piston side below
rings is baked oil caused by combustion
gases blow-by. Improper oil or poor ring
sealing is the cause.Very light scoring of the piston skirt is
likely from foreign material passing through
the engine. It does not suggest a problem in
the engine and piston replacement is not
required.Always check piston to cylinder wall
clearance to make certain the wear limit has
not been exceeded.Deposits should be removed from the piston
dome and cylinder head using a wood or
plastic scraper. Excessive deposits
collection will increase the compression
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ration and reduce heat transfer.
This piston is NORMAL in appearance.The deposits on the piston dome are from
the oil and ash, fuel contaminants and
unburned carbon. As the thickness increases
with operating time, the color gets brighter
because of higher surface temperatures.Depending on gasoline and oil used, normal
deposits may also be brown, from light tan
colour to almost black dark brown.Heavy black deposits on the piston dome are
unburned carbon accumulated because of
too low temperatures resulting from light
load operation or too rich a mixture.Brown or black varnish on piston side below
rings is baked oil caused by combustion
gases blow-by. Improper oil or poor ring
sealing is the cause.Very light scoring of the piston skirt is
likely from foreign material passing through
the engine. It does not suggest a problem in
the engine and piston replacement is not
required.Always check piston to cylinder wall
clearance to make certain the wear limit has
not been exceeded.Deposits should be removed from the piston
dome and cylinder head using a wood or
plastic scraper. Excessive deposits
collection will increase the compression
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ration and reduce heat transfer.
Seized PistonsThe piston shows yellow spots on the dome
and seizure marks on the skirt but there is
no sign of metal aluminum.If you inspect an engine and find yellow or
yellow-orange deposits on the piston dome,
that engine has experienced an abnormal
combustion condition known as detonation.
In this situation, combustion begins normally
with ignition from the spark plug but as theflame front moves across the combustion
chamber, rather than burning smoothly, the
unburned portion of the charge
spontaneously ignites. This results in
extremely high temperatures and a shock
wave heard as "pinging." What has happened
is combustion has been completed in about
29 degrees or crankshaft rotation instead
of the normal 50.The oxide of calcium, an element found in 2
- stroke oil additives, is normally near white
in colour. At temperature very near that of
the melting point of the piston, the oxide
will change colour from white to yellow-
orange and is an indicator that the engine
was overheated. The excessive heat results
in rapid piston expansion and possible failureof the lubrication film.Possible causes: too low an octane fuel used or fuel with too
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much alcohol used jetting too lean or failure of the fuel
system, i.e., clogged fuel line or filter, fuel
tank not venting, problem with fuel pump,carburetor,m air leak into crankcase spark plug heat range too hot ignition timing too far advanced, possible
failure of the c.d. amplifier box restricted exhaust system: back pressure
too high overheated, loosely-installed spark plug
Seized PistonsThe piston shows yellow spots on the dome
and seizure marks on the skirt but there is
no sign of metal aluminum.If you inspect an engine and find yellow or
yellow-orange deposits on the piston dome,
that engine has experienced an abnormal
combustion condition known as detonation.
In this situation, combustion begins normally
with ignition from the spark plug but as the
flame front moves across the combustion
chamber, rather than burning smoothly, the
unburned portion of the charge
spontaneously ignites. This results inextremely high temperatures and a shock
wave heard as "pinging." What has happened
is combustion has been completed in about
29 degrees or crankshaft rotation instead
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of the normal 50.The oxide of calcium, an element found in 2
- stroke oil additives, is normally near white
in colour. At temperature very near that ofthe melting point of the piston, the oxide
will change colour from white to yellow-
orange and is an indicator that the engine
was overheated. The excessive heat results
in rapid piston expansion and possible failure
of the lubrication film.Possible causes: too low an octane fuel used or fuel with toomuch alcohol used jetting too lean or failure of the fuel
system, i.e., clogged fuel line or filter, fuel
tank not venting, problem with fuel pump,
carburetor,m air leak into crankcase spark plug heat range too hot ignition timing too far advanced, possible
failure of the c.d. amplifier box restricted exhaust system: back pressure
too high overheated, loosely-installed spark plug
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Piston dome damage
The piston shows melted areas on the dome
and seizure marks on the skirt.
Detonation results in extremely high
combustion chamber temperatures. That
rapid heat rise, if allowed to continue, will
heat combustion chamber deposits and
spark plug electrodes to the point that they
will ignite the charge before the spark at
the plug does.This condition is called runaway surfaceignition or pre-ignition. Once pre-ignition
occurs, the temperature rise is so rapid
that melting point of the piston is reached
while the engine is still running. Metal will
melt away beneath the spark plug or in areas
of high heat retention such as at the ring
positioning pin.A complete breakdown of the lubricationfilm also occurs resulting in severe seizure.
Detonation always precedes pre-ignition and
the causes for this abnormal combustion are
the same as those for detonation.
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Piston dome damage
The piston shows melted areas on the dome
and seizure marks on the skirt.
Detonation results in extremely high
combustion chamber temperatures. That
rapid heat rise, if allowed to continue, will
heat combustion chamber deposits and
spark plug electrodes to the point that they
will ignite the charge before the spark at
the plug does.This condition is called runaway surfaceignition or pre-ignition. Once pre-ignition
occurs, the temperature rise is so rapid
that melting point of the piston is reached
while the engine is still running. Metal will
melt away beneath the spark plug or in areas
of high heat retention such as at the ring
positioning pin.A complete breakdown of the lubricationfilm also occurs resulting in severe seizure.
Detonation always precedes pre-ignition and
the causes for this abnormal combustion are
the same as those for detonation.
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Piston dome damage
The piston shows melted areas on the dome
and seizure marks on the skirt.
Detonation results in extremely high
combustion chamber temperatures. That
rapid heat rise, if allowed to continue, will
heat combustion chamber deposits and
spark plug electrodes to the point that they
will ignite the charge before the spark at
the plug does.This condition is called runaway surfaceignition or pre-ignition. Once pre-ignition
occurs, the temperature rise is so rapid
that melting point of the piston is reached
while the engine is still running. Metal will
melt away beneath the spark plug or in areas
of high heat retention such as at the ring
positioning pin.A complete breakdown of the lubricationfilm also occurs resulting in severe seizure.
Detonation always precedes pre-ignition and
the causes for this abnormal combustion are
the same as those for detonation.
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Piston damage by foreign materialPiston shows imprints of small cylindrical
parts on the domePossible Cause needles of broken wrist pin bearing
trapped in the squish area between the
piston and head, destroy the dome, ring land
and rings. make certain to check the condition of the
big end rod bearing and cage
Piston damage by foreign materialSmall ball shaped imprints on piston domePossible Cause foreign material, e.g. a pop rivet head, has
entered the engine and was trapped in the
squish area, before leaving through theexhaust port. In some cases the engine
continues to run normally until the ring fails
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Piston damage by foreign materialPiston shows a vertical groove on the skirt
connected to the wrist pin hole.Possible cause: A wrist pin circlip has come loose and was
trapped in the transfer port window. Note always use NEW circlips when
rebuilding an ultralight aircraft engine.
Piston with lubrication failure
(no signs of detonation on dome)Piston shows scoring marks below the rings
on the intake side.Possible Cause Snow or water has entered the engine and
destroyed the oil film if the piston has scoring on the
intake and exhaust sides but the
dome shows no signs ofabnormal combustion, the engine has been
run with too little or no oil. Check the
operation of the oil injection system or the
amount of oil in the premixed fuel. Also,insure proper piston clearance. if the piston has scoring on the intake and
exhaust sides, no signs of abnormal
combustion on the dome and is very dark in
color, there has been a failure of the
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cooling system. Check the fan belt, or
collant level etc.
Piston with lubrication failure
Piston shows dark brown deposits all over
the skirt.Possible Cause wrong oil quality, e.g. gear oil, automotive
oil unnecessary additives have been used inthe fuel, i.e. octane boosters, high
performance additives, upper cylinder
lubricants, etc.
Piston with lubrication failurePiston shows scuffing marks on the exhaust
side of the skirt without corresponding
marks on the intake side. The lubrication
film failed under thermal load on the
exhaust side of the pistonPossible cause: Poor quality of oil.
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Piston ring scuffing
Cylinder liner shows scoring areas, which are
exactly limited to the ring travel zone.
Beside the blue colored vertical stripes, thesurface is in good condition. The rings show
corresponding dark colored marks. The
reason is a breakdown of the lubrication.Possible Cause improper break in period poor oil quality not enough oil in premixed fuel low delivery rate from oil injection system
Piston fracture
Material fatigue fracture can sometimes e
observed on pistons of high speed engines,however, skirt fracture is usually the result
of excessive piston to cylinder wall
clearance.
Other possible causes: connecting rod breakage damage due to bad handling, crankshaft locking via piston blocking engine has ingested foreign material