Pistons

cypriotcamelUrban and Civil

Nov 29, 2013 (3 years and 6 months ago)

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Pistons

Piston Design Considerations


Pistons must:


Contain cylinder pressure


Transmit the pressure created by combustion to
force on the connecting rod


Provide a place for oil control and compression
rings to be located


Piston Design Considerations


Pistons must:


Be rigid enough to not deform under the
tremendous pressures and forces encountered


Be ductile enough to absorb pressure peaks and
not shatter


Retain the proper shape under the extreme
temperatures encountered


Piston Construction


Materials


Cast iron (used in very old engines)


Cast aluminum (most common)


Forged aluminum


Hypereutectic alloys (high silicon content
aluminum)


Carbon Graphite (being tested)


Piston Construction

Piston Construction


Piston head


Round


Approx. .040 undersized


Ring grooves


Ring lands


Drain holes and slots


Wrist pin boss

Piston Construction


Reinforcing struts


cast pistons contain
steel struts to control expansion and aid in
wrist pin support


Lock ring grooves


for full
-
floating piston
pins


Piston skirt


Full skirt


Partial skirt



Piston Construction


Cam ground pistons.


Most pistons are cam ground, this means they
are not perfectly round.


The diameter is larger on the non
-
thrust sides,
because they tend to expand more as the
temperature of the piston increases.


Piston taper


pistons may be tapered from
top to bottom

Piston Construction


Piston Pin Offset


The piston pin is offset towards the major thrust
side of the piston to reduce piston wear, and
piston noise


The major thrust side is the side that is loaded
during the power event


The minor thrust side is the side loaded during
the compression event

Major/Minor Thrust

Piston Direction

Pistons should be positioned so arrow, dot or other marking
faces the front of the engine (except reverse rotation
engines)

Piston Head Design


Pistons may have a dished, flat or domed
design

Piston Inspection


Abnormal skirt wear


Scoring


Melted aluminum or pits in the head


indicates detonation


Cracks


check ring lands, pin boss, and
skirt closely


Pin bore


check for scoring and wear