BOLT 6V5218 - Caterpillar

Initial Inspection
Several initial steps should be completed when you troubleshoot engine vibration.
Ask questions of the engine operator in order to determine the following information:
Determine the components that are vibrating.
Determine the rpm range when the vibration becomes noticeable.
Obtain a service history of the engine in order to isolate the vibration problem.
Inspect the following components: mounting frame, mounts, brackets and fasteners. Inspect weld joints that may be broken or show signs of cracking. Replace components that are broken or bent. Inspect the alignment of components that are belt driven. Tighten any components that may be loose.
Inspect the flexible engine mounts. Replace any mounts that show deterioration.
Check the condition of the crankshaft vibration damper. Ensure that the bolts are tightened to the proper torque. Check that the crankshaft vibration damper is in good repair. Also, check the damper for physical damage. Refer to Testing and Adjusting, "Vibration Damper - Check".Vibration Analysis
Further analysis requires the use of a vibration analyzer. Any instrument which can accurately measure the displacement of the vibration and the frequency of the vibration will be sufficient. Ensure that the measurement is from peak to peak of the vibration. The displacement of the vibration is measured in mils-inch/1000. The frequency of the vibration is measured in cycles per second.Record all vibrations that are over 4.0 mils. When the vibration occurs, record the engine rpm. Intervals of 100 rpm are sufficient. Record the data with the instrument filter OUT. Note any sudden increase or decrease in amplitudes. A sudden change may indicate the resonant speed range.If no magnitudes exceed 4.0 mils, the engine is within Caterpillar specifications.If magnitudes exceed 4.0 mils, the vibrations must be measured with the instrument filter IN position in order to obtain the frequency of the vibrations.Note: The 221-2370 Vibration Analyzer can be used in order to measure engine vibration. Refer to Operation Manual, NEHS0525 for additional information on the usage of a vibration analyzer.
Measure the vibration of each component that is observed to have excessive vibration.Run the engine slowly through the speed range and measure the vibration with the instrument filter OUT. When the peak amplitudes are found, continue to run the engine at the peak amplitude speeds. With the instrument filter IN, find the frequency of the vibration.
If the frequency of vibration is 1/2 times of engine rpm (1/2 order), the vibration is caused by a misfiring cylinder. This must be corrected before further vibration analysis is made.
If the frequency of vibration is 2 times the engine rpm (second order), no corrective action can be performed on the engine because this is the firing frequency of the engine. The problem is in the resonance of equipment in the surrounding area.
If the frequency is not 1/2 order or third order, then further measurements must be made on the engine.
If the vibration of the suspect components does not yield reliable data, you may measure the vibrations on the engine. In order to acquire measurements directly from the engine, measurements must be made perpendicular to the crankshaft.