Yes, FLYWHEELS is a Scrabble word!

Letter values in Scrabble US: F 4, L 1, Y 4, W 4, H 4, E 1, E 1, L 1, S 1.

Is it a valid word?

FLYWHEELS is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

regulator consisting of a heavy wheel that stores kinetic energy and smooths the operation of a reciprocating engine