After I have removed my blade for sharpning. On my Crafstman self propeled push lawn mower model # 917.378900. I put the blade back on tighten the bolt so the blade does not move, I start the mower and there is a clanking sound from under the deck. So I find that the blade is loose again, so I tighten up the blade and then start my mower again then my blade adapter breaks.

Lee Zwart, September 2005

the blade adapter will keep breaking also if the fly wheel key is broken. and make sure your blade is balanced - that may have been why one, or the other, or both broke in the first place. you can get a new fly wheel key for a few bucks at ace hardware.
lowes sells the blade adapter for about $10. oh, and both stores should have a blade balancer. looks like a devo hat, like a terraced cone shaped thing.

link for flywheel key replacement...

http://www.youtube.com/watch?v=vWcIiZtvbug

matt, November 2009

Hi Lee, The blade adaptor is made of a soft material so it will break before serious damage is done to the engine if you hit something with the blade. It is possible it wasn't quite tight enough the first time you tightened it and it cracked or damaged the key. Replace it and tighten it down good you should be ok.
GOOD LUCK

JOHN @ RONA, September 2005