The blade adapter on my lawn mower was cracked. I replaced it and as I started the mower it broke again!?

Question

The part was the correct part from Craftsman. It just sputtered a few times as if it was going to start and then it died. When I checked the adapter, the key inside had broken off.

Answer 1

If you sheared your timing key it is a good possibility that your fly wheel key is also sheared and will need replacing.
It will make your engine snap back and cause that adapter to shear again.
The other case known is when the it is not fastened tight enough.
I believe it takes a 9/16 socket, so tighten it up good.

Answer 2

First, why was the firt adapter cracked? Did you hit something? I would check for a bent crankshaft or the blade hitting something under the mower. Did the second adaptor break or just the key? If it was just the key you may not have gotten the adaptor all the way on the shaft. These are pretty tough parts and don't usally break. You may want someone to look at it for you, could be a major safety hazard. You don't want parts spinning at 3,500 rpm to brake or come apart.