Some times my car will not start. The starter turns but does not engage the flywheel. I have put a new battery in. If I boost the car with a battery charger it will start. I have checked connections and they are good. When it won't start if I keep trying it will start sometimes but not others.

 

Sounds like a starter solenoid or Bendix drive starting to fail. Same thing happened to me. Unless the starter gear gets thrown forward to engage the flywheel all you will hear is the starter motor turning. Maybe fixable without getting a new starter, depends on how much time and effort you want to spend
Have fun

 

Thanks

 

Put new starter in and works fine.

 

The solenoid does two when the key is turned to "start":

1. Kicks the starter drive out.
2. When it kicks the drive out, this action completes the circuit that spins the starter.

If the motor is spinning, the solenoid is doing what it supposed to be doing. In the OP's case, it's the sprag n the drive that's faulty.