921603-0518 Tohatsu SCREW

Introduction
Do not perform any procedure in this Special Instruction until you read this information and you understand this information. Refer to Special Instruction, SEHS7914 for any additional information.This Special Instruction provides a procedure for the diagnosis of the engine related linear vibration problems for On-Highway Engines. The following Special Instruction will provide a method that will tell if the engine complies with Caterpillar's allowable vibration levels. Illustration 3 shows the complete troubleshooting procedure. Vibration complaints arise due to objectionable levels of vibration in the operator's compartment. Vibration problems are usually caused by one of the following:
Defects in the engine mounting due to misalignment or improper design
Defects in the cab mounting due to misalignment or improper design
Misalignment or equipment on the engine is not balanced.
Chassis resonance with orders of vibration in the engine that are standardThe above defects contribute to vibrations that may appear to the operator to be caused entirely by the engine. The troubleshooting procedure for the engine vibration that follows has been designed to diagnose the true source of the vibration with a minimum unnecessary expenditure of time and material.A vibration meter that measures the amplitude of displacement and frequency is needed to perform the vibration analysis. 221-2370 Vibration Analyzer Group can be used to perform these tests. For more information, refer to Tool Operating Manual, NEHS0850.
Illustration 1 g01299034
221-2370 Vibration Analyzer Group Instructions for Completing the Engine Vibration Questionnaire
The engine vibration questionnaire is a way to record the history of engine vibrations. The engine vibration questionnaire is a way to identify vibrations from nonengine components. A dynamic analysis is required when the vibration occurs while the vehicle is in motion. In most cases, the engine is not the cause of the vibration when this situation occurs. Instead, look for the components of the drive train that are out-of-balance or components that have been deformed due to the torque reaction.Comments about suspected components are listed on the engine vibration questionnaire. If nonengine sources of vibration are discovered, consult the manufacturer of the chassis for assistance.
Illustration 2 g01298844
Flow Chart for Troubleshooting Engine Vibration
Illustration 3 g01298621
Discussion of Troubleshooting Procedure
The complete troubleshooting procedure is outlined in Illustration 3. (A) Complete the questionnaire to establish the nature of the excessive vibration complaint.
If the vibration occurs when the vehicle is stationary, proceed to the in-chassis vibration test. Interpretation of the data from the in-chassis test of vibration will provide information about the cause of the vibration and possible corrective action. The only reliable method in order to determine if the engine complies with Caterpillar allowable levels of vibration is to perform an isolated engine vibration test.
In some circumstances, even if the vibration occurs when the vehicle is moving or the engine is under load, it may be necessary to verify that the engine vibration is within specification. Under these circumstances, proceed to the isolated engine vibration test. Determine if the isolated engine complies with Caterpillar's allowable vibration levels. (B) Determine if the condition is static or if the condition is dynamic. Follow the proper procedure. (S1) Perform a speed sweep. (S2) Visually inspect all brackets and mounts for looseness. Visually inspect all brackets and mounts for seizure. Mounts or brackets that are loose or frozen can cause loss of isolation. Loss of isolation causes a transfer of energy into the chassis. This will cause resonant conditions. (S3) Performing an evaluation of the clutch can identify a failed clutch. Performing an evaluation of the clutch can identify an unbalanced clutch. A cracked center plate or a cracked disc can cause vibration in static conditions or dynamic conditions. (S4) Acquire data in order to verify that the clutch is the problem. Repair the clutch. (S5) Acquire data. Utilize a speed sweep to determine the highest amplitude of complaint. Proceed to acquire data at the engine rpm. Pay special attention to the units of the data points. Refer to Table 1 for On-Highway Truck Engine route points. Refer to Special Instruction, SEHS7914 for details on analysis and tables for data.Note: If the cab component is the basis of the complaint, obtain data at this point. Determine the amplitude and the frequency. (S6) Interpret the data. Training is required for analysis of the data to avoid any misinterpretation of the data. Refer to Special Instruction, SEHS7914 for fundamental orders and causes.
Confirm the complaint of the customer at the location.
Measure the vibration. Determine the frequency and amplitude at the location with a magnet or a stinger.
Determine the order of the vibration relative to the the engine's rpm.
If the engine order can be divided by 1/2, continue to the engine route locations.
If the amplitude of the frequency of the complaint is within limits, the problem is not the engine.
If the engine order of the complaint cannot be divided by 1/2, determine if the problem is one of the gear train frequencies. Refer to Table 3.
If the component of the complaint is in resonance, there will be amplification of the exiting order between the engine and component. Use the analyzer to find the resonant point.
If the frequency does not correspond to an engine order, it could be driveline related. Possible causes could include the transmission, the drive shaft or the tire. For further assistance, contact the Caterpillar Tier 2 Support staff for Truck Engines.
If the complaint only happens under loaded conditions, a test while the vehicle is being driven is required. Place the velometer under the seat or on the steering column in order to obtain a route point.
If the measurement point requires placing the pickup on a small object such as a shift lever, do not restrict movement with the stinger.
The optional accelerometer is available to determine complaints for frequencies above the eighth order. The complaints are usually associated with a sound. Special routes are required for this sensor.
If the frequency is related to an engine excitation, determine the method the energy is transmitted to the excited component. The analyzer with the stinger can be used to monitor the motion across piping, mounts, frame and components to determine amplification of