I managed to remove the clutch rotary assembly which had a broken spring and need to be replaced. There is another item that has to be removed in order to remove the pull cord housing. Said item requires a wrench and must be turned counter-clockwise in order to be removed. The problem is that I am unable to prevent the drive shaft from spinning. I tried placing a screw driver in the fins to stop the shaft from turning but to no avail (damaged a fin).

The trimmer is a Troy Bilt (Big Boy) Model TB575SS. I checked online and noticed the engine parts schematic does not show that item in question.

Thank you very much.
Francis

There's an old shop trick of placing pull rope into the cylinder through the spark plug hole. Also, there is the spark plug cylinder locking tool that threads in just like a spark plug that has a long piece of rod shaped plastic that sticks down into the cylinder. The trick to the rope is to use clean rope, and have the piston all the way down, place the rope into the cylinder, and slowly turn the engine until it "locks". Then turn the engine the opposite direction to remove the rope.