Follow the sequence of steps on the troubleshooting chart. The troubleshooting chart will provide a logical procedure to determine the frequency and amplitude of vibration. This chart allows the source of vibration to be located and corrected.
- Ask questions of the customer that will help to determine the following information:
- Determine the components that are vibrating.
- Determine the range of speed when the vibration becomes excessive.
- Check the history of the problem.
- Look for any loose mounts, brackets, and fasteners. Look for any broken mounts, brackets, and fasteners. Repair any fixtures and tighten any fixtures.
- Further analysis requires the use of a vibration instrument. Any instrument which can accurately measure the displacement of the vibration will be sufficient. The displacement of the vibration is measured in mils-inch/1000 and the frequency of the vibration is measured in cycles per second.
Note: The following steps assume the use of a vibration instrument such as the IRD Mechanalysis Model 320 or an equivalent instrument can be used to analyze vibration. Refer to Special Instruction, SEHS7914, “Troubleshooting Engine Vibration In Vehicular Equipment” for additional information for troubleshooting the vibration complaints.
- Measure the vibration of the components which have the objectionable vibration.
Run the engine slowly through the speed range and measure the vibration with the instrument filter “OUT”. When 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 the 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 3 times the engine rpm (3rd order), no corrective action can be performed on the engine because this is the firing frequency of the engine.
If the frequency is not 1/2 order vibrations or 3rd order vibrations, then further measurements must be made on the engine.
- Measurements that are taken on the engine must be made perpendicular to the crankshaft. Take the measurements at the front and at the rear of the engine in vertical and in horizontal directions.
- Record all vibrations that are over 4.0 mils. When the vibration occurs, record the engine rpm. 100 rpm intervals are sufficient. Perform the recording with the instrument filter “OUT”. Note any sudden increase and decrease in amplitudes. The sudden increases and sudden decreases are called the resonant speed range.
If no amplitudes exceed 4.0 mils, the engine is within Caterpillar specifications.
If amplitudes exceed 4.0 mils, the vibrations must be measured with the instrument filter “IN” in order to obtain the frequency of the vibrations.
- Run the engine at high idle. With the instrument filter “IN”, check the frequency range and record any amplitudes over 4.0 mils and the corresponding frequency. Analysis of the possible cause of the vibration is accomplished by performing the following procedures: identify the frequency of the vibration. and location of the vibration with the greatest magnitude.