Damaged unit parts due to high engine speed
Engines are designed to operate at a maximum permitted speed. This engine speed is not exceeded when the vehicle is driven normally. However, driving and operating problems (e.g. “changing to the wrong gear” on vehicles with manual transmission) or manipulation (e.g. tuning) can cause the maximum permitted engine speed to be exceeded when the vehicle is driven.
Overspeed events are stored in the DME control unit. The following values are also recorded:
* Number of ignition attempts in each overspeed range. ⇒ overspeed range = Defined rev ranges with classification of expected engine damage, e.g. engine damage possible, … probable, … very probable, engine damage has generally occurred; see section ⇒ ‘Overspeed event range interpretation‘.
* Status of the hourmeter during the last overspeed event ⇒ for technical reasons, overspeed events are entered in a preset time interval. As a result, there may be entries in a higher rev range while no entries are stored in the lower range.
* Ignitions are 3 per revolution. Overspeed ignitions of two or less in a range may be considered an error (incomplete revolution).
* If overspeed entries are found and if the difference between the current hourmeter and the status when the last overspeed event was recorded is less than 50 operating hours, there is a high probability that the damage was caused by overspeed event(s).
* The value “50 operating hours” should be seen as a guide. The possibility of engine damage occurring much later due to previous overspeed event(s) cannot be ruled out.
* Overspeed events for PDK can be disregarded.
Overspeed event range interpretation
* Rev range 1: ⇒ Maximum permitted engine speed exceeded; engine damage possible.
* Rev range 2: ⇒ Maximum permitted engine speed exceeded; engine damage possible.
* Rev range 3: ⇒ Maximum permitted engine speed exceeded; engine damage possible.
* Rev range 4: ⇒ Maximum permitted engine speed clearly exceeded; engine damage probable.
* Rev range 5: ⇒ Maximum permitted engine speed very clearly exceeded; engine damage very probable.
* Rev range 6: ⇒ Engine damage has generally occurred.
Typical faults and symptoms as a result of overspeed events may include the following:
* Damaged valves and/or pistons (impact marks on the valve, valve impressions on the piston, valve bent).
* Cylinder liner damage (even “piston seizure”).
* Damaged or displaced connecting rod bearings.
* Loosened or loose fastening screw(s) on the crankshaft pulley.
* Loosened or loose fastening screw(s) on the camshaft gear.
* Loosened or loose connecting rod bolts.
* Cracked timing chain(s).
* Changed timing.
* Irreparably damaged clutch elements (pressure plate and/or drive plate).
* Vibrations and/or engine imbalance due to irreparably damaged clutch elements.
* Vibrations around the transmission.
* Defective synchronisation.
Overspeed event calculator
* See the model table below for by model RPM ranges to input to the calculator.
* Use the lowest value in a range (Min) for most conservative estimate.
* Use the highest value in a range (Max) for least conservative estimate.
* Do not mix Min and Max values for calculation.