Causes And Correction Of Opposite Crankshaft Rotation In Direct Injection Engines

There have been reports of direct injection engines experiencing brief opposite rotation of the crankshaft. There are several conditions which can lead to opposite rotation of the crankshaft. Most of these conditions occur when there is excessive engine load at low idle rpm. Opposite crankshaft rotation is also more likely to occur after the engine reaches operating temperature.

Here are some examples of conditions which could cause opposite crankshaft rotation.

1. The engine is made to lug excessively at low idle rpm by suddenly increasing the load from either the hydraulic system or drive train. Hydraulic control systems normally have a check valve between the pump and the implement to prevent reverse oil flow to the pump. However, residual pressure in the hydraulic system can briefly become greater than the torque available from an engine lugged at low idle rpm. When this happens, a force goes through the hydraulic pump in the opposite direction.
2. Engine cranking is interrupted before full cranking speed is reached. This is sometimes called “bump starting”. It causes compression in the combustion cylinders and “kicks” the crankshaft in the opposite direction. Bump starting with a load on the engine can increase the chances of opposite crankshaft rotation.
3. If the machine is in a forward speed and goes in a reverse direction (backs) down an incline, the momentum in the reverse direction can be greater than the available engine torque. This can briefly turn the crankshaft in the opposite direction.
4. The low idle rpm is below specifications.
5. The engine turns slowly when being started due to low battery charge or poor battery connections.

To reduce the chances of having opposite crankshaft rotation, Caterpillar recommends the following:

1. Make sure that all operators are warned against lugging the engine at low idle rpm.

2. Discourage operators from shifting from a forward speed to reverse while the vehicle is in a forward direction.

3. Instruct operators to bring the engine rpm to full cranking speed before the starting mechanism is disengaged.

4. Discourage operators from using a forward gear to brake the machine as it goes in a reverse direction down an incline, especially if the engine is in low idle rpm.

5. Adjust low idle rpm to meet specifications.

6. Make sure that batteries and starting system connections are in satisfactory condition to give full cranking power to the starter.

If opposite crankshaft rotation does occur, Caterpillar recommends the following actions:

1. Shut the engine off immediately.

2. Inspect the air cleaner elements for damage or plugging. Replace if necessary.

3. Restart the engine and observe the oil pressure. If it is normal, operate the engine for five minutes. Shut off the engine, replace the oil filter, and inspect the used oil filter for any evidence of engine bearing damage.

4. Take an engine oil sample for analysis.

5. Take an engine oil sample for analysis every 50 hours of operation until the next scheduled oil change.

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