12/2/2008
Manufacturer Tech Tip: Spin Testing Caution
Many engine builders use a test stand that
motors the engine using an external power source. Duration of this testing must
be held to an absolute minimum and a test oil, with a high "EP"
additive content, used to prevent damage to critical cam lobe and follower
surfaces.
Typically the engine is fed a light oil by a pump within the test stand to
simulate hot operating conditions. The engine is motored by the external power
source at a speed of less than 500 rpms for 2 or 3 minutes while oil pressure,
oil flow and torque required to spin the engine, are monitored..
Occasionally a camshaft failure develops following the test and subsequent
installation into a vehicle or power unit.
The speeds generated during this test are too low compared to those required
for proper camshaft and lifter break-in. Since the camshaft in a 4-cylinder
engine rotates at only one half crankshaft speed, the low rpms do not create
sufficient inertia force to "toss" the lifter off the lobe apex which
is necessary to reduce the loading on the nose or apex of the cam lobe. This
reduction in loading at higher engine speeds prevents scuffing and wear of the
lifter and lobe contact surfaces.
The thin test oil being circulated also tends to flush the camshaft break-in
lubricant from the lobe and lifter surfaces.
Then with the engine delivered to the installer the camshaft is protected
only by the residual test oil. If the installer experiences problems firing the
engine, or delays the break-in procedure for any reason, metal to metal contact
is likely to occur; resulting in a lobe failure.
Tech Tip courtesy of MAHLE Clevite
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