Small Engines (Lawn Mowers, etc.): Tecumseh lawnmower engine, blade holder, drive shaft

Question
Tecemseh vector engine 6H.P. on Ariens mower.  A couple of years ago the mower started making a knocking sound when starting, then progressed to being noisy when running.  Neighbour suggested it was a "key" on the shaft above the blade.  Took it to dealer and that is what it was.  Has started again.  I'm somewhat handy (wife will not agree). Can you tell me how to replace this "key" and should I be looking for another problem seeing as how it was fixed only two years ago.  
Thank you very much in advance
Dave  

Answer
Hi Dave,

If it is the key for the blade holder, you would need to remove the blade and the holder from the drive shaft.  The key is located on the shaft or in the holder.  Problems that might cause this are:  A loose holder bolt, an unbalanced blade or by hitting objects.

Let me know how you make out.
Michael