The effect of "Morphtronic Engine" makes the equipped monster's current ATK equal to twice its original ATK. The new ATK value is not considered to be the monster's original ATK.
If the Level of the equipped 'Morphtronic' monster changes to a value other than 3, "Morphtronic Engine" is destroyed.
If your second Standby Phase after activating "Morphtronic Engine" is skipped, or if the "Morphtronic Engine" cannot be destroyed (due to "Magic Reflector", etc.), "Morphtronic Engine" is not destroyed and remains equipped to the 'Morphtronic' monster. The monster's original ATK remains doubled.
The effect to destroy the equipped 'Morphtronic' monster during your second Standby Phase after activating "Morphtronic Engine" starts a Chain.
If a 'Morphtronic' monster is equipped with 2 or more copies of "Morphtronic Engine", the additional copies are redundant because only the monster's original ATK is doubled.