I've just resurected an old puch one speed motor and the piston is knocking like crazy. Only when I'm on the bike though, when it's on the stand it appears to be fine. There is no play in the rod bearings, nor is there play between the wrist pin and upper rod sleeve, yet there is play on the wrist pin between the sir clips...like the wrist pin isn't snug in the piston. I've adjusted the timing but maybe I need new points? Anyone ever have a similar problem? Solution?