Is the clutch overheating due to
slippage? If the shoes are worn, or if your springs are too stiff
or if you've gotten oil or grease in the bell, you could get slippage.
in that case the shoes are not engaging properly and slipping. this
causes the bell to heat up excessively. This heat can/will destroy the
bearings quickly! The solution is to clean the bell and or replace the
shoes. If the spring is too stiff you might try a weaker spring.
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One of the most common causes of
clutch bearing failure is improper lubrication. Soaking them in any
type of oil is a mistake. Once it heats up the oil migrates down the
shaft into the clutch = heat = toasted bearings. Use a high melt temp
extreme pressure grease in all the sealed bearings. This grease is
designed for extreme bearing applications and does not migrate at
operating temperatures. Many racers also have success cleaning all the
lube out of the clutch bearings then re-oiling with one-half to one
drop of Mobil 1/Prolong/etc.
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Is the clutch bell hitting the
chassis when it flexes? Look closely directly under the bell for
a rub mark. If it comes in contact with the chassis at all this
can cause blown bearings. The solution here is to use better
braces to keep the chassis from flexing. If this isn't possible
or a quick fix is needed at the track shims/washers can also be used to
raise the entire engine assembly a little.
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Is the clutch assembly getting
too hot? Many clutch bells turn into a blue color instead of normal
black when overheated. If one is available use a temp gun at the
end of a hard run. An excessive temperature at the front of the
bell indicates resistance or a vibration problem. At installation
the bell should spin completely free and there should be a little
"play" (about 0.5 mm). This allows the parts to expand when they
heat up without binding. Other possible causes of excessive heat are a
clutch spring that has become weak (allowing one shoe to constantly
drag) or a worn or broken clutch shoe.
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Check both engine bearings. Play
in either will cause clutch bearing wear by allowing the crankshaft to
vibrate at high RPMs. If the front engine bearing leaks fuel this can
migrate into the clutch causing the failure.
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A slightly warped crankshaft can
also vibrate clutch bearings to death quickly. This is the most
difficult problem to run down since the shaft does not have to be
noticeably warped to cause bearing damaging vibration at high RPM.
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The clutch bell itself can also
be a bearing eater if it has developed an out-of-round (warped)
condition or has been manufactured out-of-tolerance. I've seen some
famous brand bells with this problem right out of the package.
The outer bell spins perfectly round but the inner bell (with the
teeth) is warped.
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