First-Order Engine Imbalance

NOTE: Do not accelerate against the brakes for longer than 10 seconds. Do not overheat the engine or the transmission. Depending on the vehicle design, the engine will only accelerate to a certain point under these conditions. Also, care should be taken during diagnosis as some disturbances may be created during brake torque that normally do not exist.

NOTE: Proper flywheel installation requires carefully WALKING the flywheel onto the crankshaft and stagger-tightening the bolts. Proper torque converter to flywheel installation then requires gradually WALKING the torque converter to be flush with the flywheel, prior to installing the bolts. Do not draw the torque converter to the flywheel with the bolts. If these precautions are not followed, warping or bending of the flywheel and/or damage to the transmission torque converter may result.




Engine imbalance is a condition that exists when a component that rotates at crankshaft speed is either unbalanced or has excessive runout. In rare cases, the crankshaft may be unbalanced. Balancing the component or correcting the runout may bring the disturbance to an acceptable level.

Symptoms
1. Vehicle shake at low speeds of 500 - 1,200 rpm, or 8 - 20 Hz
2. Roughness and BOOM at higher speeds of 1,200 - 3,000 rpm, or 20 - 50 Hz
3. Vibration usually detected during the Neutral run-up test

Isolating the Components
1. Perform the Neutral run-up test, noting the RPM at which the vibration is the worst, and the most severe. Refer to Types of Road Test Procedures.
2. Inspect all powertrain mounts. Repair or replace as needed.
3. Inspect for any bindings or ground-outs in the exhaust system.

Important: Steps 4 - 17 apply only to vehicles equipped with automatic transmission.

4. Mark the location of the torque converter to the flywheel.
5. Disconnect the torque converter from the propeller shaft, pushing the converter back from the flywheel.
6. Tie up the converter, away from the flywheel.
7. Perform the Neutral run-up test again. Observe the flywheel. If the flywheel shows any wobble or lateral runout, replace the flywheel.
- Re-index the torque converter in 3 different positions.
8. If the disturbance still exists, replace the torque converter.
9. If the vibration still exists, inspect the propeller shaft runout. First-Order Driveline Vibration.
10. If the vibration still exists, inspect the harmonic balancer.
11. If the vibration still exists, the problem is related to residual engine imbalance.

Correcting Residual Engine Imbalance
1. Install the washers on the harmonic balancer pulley bolts.
2. Replace the bolts with longer bolts of equal hardness as needed.
3. Install the J-nuts on the outer edge of the circular holes in the flywheel.
4. For M/T only, inspect the flywheel and the pressure plate for the following conditions:
- Correct factory indexing (The white paint spot on the flywheel and the pressure plate should line up.)
- Warping
- Balance