1. Piston Design &
Failure Analysis

2. Piston Function
Transfer energy to the
crankshaft.
Control expansion under warm-
up.
2

3. A
typical
piston
illustrati
ng the
various
parts
and the
names .

4. Piston Heads (Crown)
Domed
Flat Top
Recessed (valve reliefs)
Dished

5. A Domed Piston with
valve reliefs or valve
pockets.

6. A Flat Top
Piston

7. A Flat Top Piston with
valve reliefs or valve
pockets.

8. A Dished Piston with
valve reliefs or valve
pockets.

9. Piston Measurements
New pistons are
measured at
dimension “H”
Used pistons
are measured at
widest point.
9

10. Piston Design
Pistons are neither
cylindrical nor round.
Pistons are made with
special materials to control
expansion.
Piston rings have special 10

11. Piston Failure
Analysis

12. 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 12

13. Heat Seizure
Excessive heat,
over 1200F/650C
EGT
Lean jetting or
adjustments on
carb
Incorrect loading
on propeller 13

14. Cold Seizure
Thermo-
imbalance of
piston and
cylinder
Lack of warm-up
Excessive
temperature 14

15. Lack of Lubrication
Excessive water
ingestion causing
loss of oil film on
intake.
Lack of intake air
filter service.
Results in excessive
clearance 15

16. Piston Dome
Breakout
Ignition timing
failure, erratic
firing.
Lack of ignition
damper, points
engines. 16

17. Piston Fracture
Complete disassembly
required to remove
all material.
Cause from excessive
wear, excessive
RPM with no load,
excessive clearance
fitting.
17