So Ive been quite suspicious of my girlfriend lately. She has been car-pooling with her ex boyfriend lately, he drives her to my house, and to there school(i go to a different school) and anyway I think their becoming more than friends again even when she says "we just friends". When he drops her off and I'm in the garage she usually gets right out of his car but if all the lights are off (they think I'm inside watching TV or outback in the shed) she sits in his car for like 20 minutes. So i decided to pull a quick one on them. One night I turned all the lights off and left the garage door open and hid behind my quad. Well his car pulled into my driveway and his headlight were shining on my quad and I noticed my sprocket was worn down and hooked should I get a new sprocket and chain or just a sprocket??