nevermind, I looked at the pics again and see the stock flywheel.
XXX, Ive never heard that term fretting, but I have seen this on a few motors including my own. All had l/w flywheels and high rpm setups
Here is the Definition.
http://en.wikipedia.org/wiki/Fretting
Kawasaki 550-440 mod flywheel/crankshaft taper surfaces were notorious for this as well.
Fretting
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For fretting in music, see
fret.
Fretting refers to
wear and sometimes
corrosion damage at the
asperities of contact surfaces. This damage is induced under load and in the presence of repeated relative surface motion, as induced for example by vibration. The
ASM Handbook on Fatigue and Fracture defines fretting as: "
A special wear process that occurs at the contact area between two materials under load and subject to minute relative motion by vibration or some other force." The
amplitude of the relative sliding motion is often in the order from
micrometers to millimeters, but can be as low as 3 to 4
nanometers[1]. The contact movement causes mechanical wear and material transfer at the surface, often followed by
oxidation of the debris and the freshly-exposed surface. The oxidized debris often act as an abrasive since it is usually much harder than the underlying
metal surfaces. However, fretting can also occur in
inert gases or in
vacuum (e.g., in space).
Contents
[
hide]
[edit] Steel
Fretting damage in
steel can be identified by the presence of
rust (iron oxide powder) and the rough, torn appearance of the pitted surface. The rust particles are much harder than the steel surfaces in contact, so
abrasive wear is inevitable.
[edit] Products affected
Fretting examples include wear of drive
splines on
driveshafts, wheels at the
lug bolt interface, and
cylinder head gaskets subject to differentials in
thermal expansion coefficients.
There is a current focus on fretting research in the aerospace industry. The dovetail blade-root connection and the spline coupling of gas turbine aerogines experience fretting during their service life.
[edit] Fretting fatigue
Fretting decreases
fatigue strength of materials operating under cycling stress. This can result in so-called fretting fatigue whereby fatigue cracks can initiate in the fretting zone. Afterwards, the crack propagates into the material.
[edit] Mitigation
The fundamental way to prevent fretting is to design for no relative motion of the surfaces at the contact.
Surface finish plays an important role as fretting normally occurs by the contact at the asperities of the mating surfaces.
Lubricants are often effective in mitigation of fretting by reducing
friction and inhibiting oxidation (e.g., reducing the exposure of the surface to air). Soft materials often exhibit higher susceptibility to fretting than hard materials of a similar type. The
hardness ratio of the two sliding materials also has an effect on fretting wear.
[2]
However, softer materials such as
polymers can show the opposite effect when they capture hard debris which becomes embedded in their bearing surfaces. They then act as a very effective
abrasive, wearing down the harder metal with which they are in contact.
[edit] See also