So a while back my motor stopped working on me. I didn't have time to check it out, so i just found a whole new motor. Now I am looking at this old motor. Nothing seems to be wrong with it, no cylinder wall damage, no cracks in the block. I have the head off of it and when I crank it, everything seems fine....there is a slight thumping noise at some point in the stroke which sounds like its coming from one of the cylinders. Could this be anything? It is really slight, and it doesn't seem like anything is impeding on the stroke or anything. Need some help. Thanks