OP amps distort sine wave
This is classic crossover distortion in LM324.

Add a load resistor to output until crossover distortion disappears.
Start with 1K to  V- or gnd if using single supply.

This occurs with capacitive loads or next stage pullup R bias to Vcc/2 perhaps.  Increase R load values as alternative if so...  ( by design in order to minimize idle current)

Datasheet 


  "For ac applications,where 
  the load is capacitively coupled to the output of the amplifier, a
  resistor should be used, from the output of the amplifier to ground to
  increase the class A bias current and prevent crossover distortion."


Note for single supply use. R1 could be 2K to V+ and 2K/Gnd
THis depends on output swing max you need.