mccullough hedge trimmer stops cutting after 5 mins use?

My tivoli 65 mccullough hedge trimmer is virtually unused at 2 years old and works well for 5 mins after start up. It then stops cutting as the blades chatter and stop reciprocating even when the motor is revved.The mechanism looks undamaged and the drive is not being disabled by the slippage lever engaging with the roller bearing linkage.

kevin mcavinchey
May 2009