Date: 03/03/97

Bulletin: TB3042

Subject: Caution on Spin Testing

Engine: All

Clevite Part Number: All

Explanation:  Many engine re-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 RPM's 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 RPM's 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.