It was definately tight. I'm using a feigao 540 10xl. I did what the instructions said for putting the o ring on. dab a pinch of oil on the rings and then put it on. I had no problem doing that.
Maybe the oil played a part in the leaking but I have absolutely no other idea on how to get the o ring on the motor while in the jacket.

For now should I probably switch to the SV27 cooling jacket? Currently got one on hand from an older project.

http://www3.towerhobbies.com/cgi-bin...?&I=LXMTZ6&P=7