Engine Over running occurs when the engine RPM crossed more than specified RPM. As per the Condition here below,

When the higher speed wheels drive the engine instead of Engine drives the wheels. This will happen when

In emergency, if the driver shifts the gear from HIGHER to LOWER without reducing the vehicle speed (ie. not using the Service brake or Engine Exhaust Brake).

Sudden engagement of gears while coasting the vehicle in downward with Neutral position that causing the power flow in reverse direction.

These results the wheels will tend to drive the engine through gears and raise the engine speed more than specified. As it increases the inertia of valve train and spring surge which will cause the Intake and Exhaust valves to operate irregularly.

This irregular Valve operation will further result in failure of valve train mechanism and consequentially damage the Piston, Crankcase and Injector etc.

Engine Overrunning Capability: 4200RPM for 15 Sec. (for reference purpose , it may vary with engine mfrs.)

Do’s & Don’ts:

Don’t Jump the Gears such as 9^th to 7^th or 5^th to 3^rd vice versa even in Plain road or while descending the hills.

Don’t over speed the vehicle while down gradient.

Don’t use the engine force as braking force by shifting higher to lower gears to reduce the vehicle speed.

Shift the gears after attained the specified speed range.

Use the Engine exhaust brake also to control the vehicle while down gradient.

Causes:

Effects: