We had that problem also. We had much better luck just tapping it through with a small brass hammer.
Originally Posted by tlewter
The clips was one issue...the second was it made me really nervous to stick the motor in the vice and drive it through.
The press fit was much greater than I expected. I was sure I was going to ruin the brand new motor...but really the toughest part of all, as you noted was getting that flippin clip off! However, everything worked out okay and I have been impressed with the 3536C motor. Again, as noted by others, the stock motor doesn't even compare at twice the cost.