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Common Causes of
Premature Camshaft Failure
The key
parts of any camshaft are the lobes. As the camshaft spins, the
lobes open and close the intake and exhaust valves in time with the
motion of the piston. It turns out there is a direct relationship
between the shape of the cam lobes and the way the engine performs in
different speed ranges.
It is highly recommended that you change the rocker arms with every cam
change and keep them together as a package or kit. The reason is,
rocker arms burnish themselves to each cam lobe. As we know, each cam
is ground on a different angle and each rocker arm wears at a different
angle. If you use rocker arms from one camshaft to another, they will
most likely trough into the new cam lobes. |
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the four most common causes of premature camshaft failure: |
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- Improper break
in procedure. Excessive or long cranking on initial start up. Engine
must start immediately and run at 1600-1800 rpm?s for 20-30 minutes
- Improper rocker
geometry, changed by: increased camshaft lobe lift, valve tip height
and rocker stand height.
- Improper valve
springs. Inadequate clearance between coils (coil bind), spring
pressure too high or spring pressure too light.
- Reground
camshafts with reduced base circle diameters will cause premature
lobe and rocker wear.
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| Rocker
Arm Burnish |
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Camshaft Burnish |
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Note: To
correct rocker arm contact pattern, mark the rocker arm with a black ink
marker, rotate engine two (2) complete revolutions, inspect contact
pattern. If ink is wiped off nose or heel of rocker arm, you will need
to adjust the rocker shaft stands.
Usually milling the stands .015? / .020? will center the pattern.
Always check valve to piston clearance. The minimum clearance should be
.100?, if using an adjustable cam gear, check with full advance and
retard to assure adequate clearance. |
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