Simplify the following text for a Grade 7 native English-speaking person.
Original: It is essential in engines with long crankshafts ( such as straight-8 engines ) and is present on most engines as it reduces torsional vibrations that tend to peak at certain speeds .
Simplified: It is needed in engines with long crankshafts , such as straight-8 engines . It is used on most engines to reduce torsional vibrations that can occure at certain speeds .