1. Piston Design &
Analysis
2-Stroke ROTAX Aircraft Engines
ROTAX FLYING CLUB - 2001
©

2. Piston Function
Transfer energy to the crankshaft
Control expansion under warm-up
Copyright ROTAX FLYING CLUB 2001 (C)
2

3. Piston Measurements
New pistons are
measured at
dimension “H”
Used pistons are
measured at
widest point
Copyright ROTAX FLYING CLUB 2001 (C)
3

4. Piston Analysis
Compare piston to cylinder for clearance
and evaluation of suitability of cylinder.
Follow latest
specifications from
Rotax using only
genuine ROTAX
Aircraft engine
parts.
Copyright ROTAX FLYING CLUB 2001 (C)
4

5. Piston Design
Pistons are neither
cylindrical nor round.
Pistons are made with
special materials to control
expansion.
Piston rings have special
functions and design.
Copyright ROTAX FLYING CLUB 2001 (C)
5

6. Piston Failure
Analysis
2-Stroke ROTAX Aircraft Engines

7. 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
Copyright ROTAX FLYING CLUB 2001 (C)
7

8. Heat Seizure
Excessive heat, over
1200F/650C EGT
Lean jetting or
adjustments on carb
Incorrect loading on
propeller allowing
excessive RPM
Copyright ROTAX FLYING CLUB 2001 (C)
8

9. Cold Seizure
Thermo-imbalance of
piston and cylinder
Lack of warm-up
Excessive temperature
difference inlet to outlet
on engine.
Copyright ROTAX FLYING CLUB 2001 (C)
9

10. Lack of Lubrication
Excessive water
ingestion causing loss
of oil film on intake.
Lack of intake air filter
service.
Results in excessive
clearance
Copyright ROTAX FLYING CLUB 2001 (C)
10

11. Oil Failure/Oil Flash
High temp in engine
from cooling system
failure, fan belt,
coolant problems.
Poor quality oils, auto,
gear, unsuitable
temperature stability.
Copyright ROTAX FLYING CLUB 2001 (C)
11

12. Piston Scuffing
Scuffing on exhaust
side with no marks
corresponding on
intake.
Thermal loading of
oil film due to poor
quality oil.
Copyright ROTAX FLYING CLUB 2001 (C)
12

13. 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)
Copyright ROTAX FLYING CLUB 2001 (C)
13

14. Piston Dome Breakout
Ignition timing failure,
erratic firing.
Lack of ignition
damper, points
engines.
Copyright ROTAX FLYING CLUB 2001 (C)
14

15. Piston Dome Detonation
Pre-ignition, leading
into detonation
Advanced ignition
timing
Spark plug heat range
too high
Low octane fuel
Copyright ROTAX FLYING CLUB 2001 (C)
15

16. 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.
Copyright ROTAX FLYING CLUB 2001 (C)
16

17. Piston Scoring/Material Damage
Objects between
piston and wall.
Complete disassembly
required to find source
and all related material
Copyright ROTAX FLYING CLUB 2001 (C)
17

18. Piston Fracture
Complete disassembly
required to remove all
material
Cause from excessive
wear, excessive RPM
with no load, excessive
clearance fitting.
Copyright ROTAX FLYING CLUB 2001 (C)
18