Rotax

Piston Design &Analysis

2-Stroke ROTAX Aircraft Engines

ROTAX FLYING CLUB - 2001 ©

Copyright ROTAX FLYING CLUB 2001 (C)

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Piston Function

Transfer energy to the crankshaft

Control expansion under warm-up


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New pistons are measured at dimension “H”

Used pistons are measured at widest point

Piston Measurements


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Compare piston to cylinder for clearance and evaluation of suitability of cylinder.

Follow latest specifications from Rotax using only genuine ROTAX Aircraft engine parts.

Piston Analysis


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Pistons are neither cylindrical nor round.

Pistons are made with special materials to control expansion.

Piston rings have special functions and design.

Piston Design

Piston Failure Analysis

2-Stroke ROTAX Aircraft Engines


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Normal Pistons

Deposits vary from oil ash, brown, tan, to black/brown. Light color denotes higher cylinder temperatures.Light scoring is normal, varnish from blow-by gas is normal


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Heat Seizure

Excessive heat, over 1200F/650C EGTLean jetting or adjustments on carbIncorrect loading on propeller allowing excessive RPM


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Cold Seizure

Thermo-imbalance of piston and cylinderLack of warm-upExcessive temperature difference inlet to outlet on engine.


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Lack of Lubrication

Excessive water ingestion causing loss of oil film on intake.Lack of intake air filter service.Results in excessive clearance


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Oil Failure/Oil Flash

High temp in engine from cooling system failure, fan belt, coolant problems.Poor quality oils, auto, gear, unsuitable temperature stability.


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Piston Scuffing

Scuffing on exhaust side with no marks corresponding on intake.Thermal loading of oil film due to poor quality oil.


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Piston Ring/Cylinder Scuffing

Oil breakdown due to: Improper break-in Poor quality oil Lack of oil in mixture Excessive loading of

engine (propeller pitch)


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Piston Dome Breakout

Ignition timing failure, erratic firing.Lack of ignition damper, points engines.


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Piston Dome Detonation

Pre-ignition, leading into detonationAdvanced ignition timingSpark plug heat range too highLow octane fuel


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Foreign Material

Material damage on piston from displaced or introduced object.Disassembly required of entire engine to find any additional material/damage and locate source.


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Piston Scoring/Material Damage

Objects between piston and wall.Complete disassembly required to find source and all related material


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Piston FractureComplete disassembly required to remove all materialCause from excessive wear, excessive RPM with no load, excessive clearance fitting.

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