completely wrecked my top end on my fx1 that i just purchased a couple of months ago and had no idea about sbt at that point. a family member told me about the core exchange so i ordered the kit and sent mine back in the box that my new kit came in. very fast shipping and very professionally packaged. ring gap and everything was good to go right out of the box and im very happy with my experience. i would highly recommend sbt for any jet skit parts or products needed. i will definitely do business here again!