Small Engines (Lawn Mowers, etc.): Flywheel Key

Question
I own a McCulloch 3818 chainsaw and I need a replacement flywheel key to fit my machine.  It is a half moon style.  I did not hit anything hard to cause the key to brake, when I replaced the key the first time I bought it from a lawnmower dealership and the gal put several keys on the countertop and said here pick from these. I found one that was a close to the one that was broken.  But after installing it into the chainsaw and used it for less then 5 seconds it broke as well.  The chain turns freely and I have never abused my saw or equipment.  It is hard to find McCulloch parts for a Mac 38.  Thank you for your time.

Answer
Something is very wrong with the saw...I have never seen a McCulloch chainsaw or weed trimmer shear a flywheel key and I have worked on thousands of units.


The 102164 McCulloch part number is available at several site for $10...too much money.

I'd take the saw to you local hardware store, as many other sites mentioned, and find the correct size.  Ace Hardware usually has a very good selection of small items like woodruff keys.

Is there a washer under the flywheel nut?  

I would also get some lapping compound and lap the flywheel to the crank taper to make sure the parts are mating correctly.

Eric