APPLICATION: Holden Commodore VP-VR from engine number VH 1274844 with 8 bolt mounting to crank.
Signs you have a cracked flex plate:
The flex plate makes a loud knocking noise as it rotates (very similar to a bent engine rod)
Motor won’t turn over
Loss of drive
A cracked flex plate is usually a sign of other problems. If you replace the flex plate and don’t fix the real problem your flex plate will most likely crack again. Installing a heavier duty flex plate will normally pass the problem on to the transmission.
Flex plates can absorb the minute misalignment between the engine and the transmission. But, as misalignment increases, the flex plate flexes more and eventually this causes the metal to fatigue and the flex plate cracks. To avoid this, misalignment should be less than 0.2 mm.
Slight misalignment may only cause a single flex plate to break in the life of the vehicle. More severe misalignment can break a flex plate in 24,000 to 48,000 km.
Other things that can cause a flex plate to crack include:
Missing or improperly tightened bolts / dowl pins
Foreign objects caught between the engine and transmission e.g. wires
Excessive crankshaft flange or end plate run-out
A damaged engine, transmission or torque converter
Hydraulic locking causing a damaged crankshaft
The same things that cause the flex plate to crack can also cause transmission problems. Damaged and leaking front seals and front transmission pumps are common symptoms.
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