I have a 1981 Honda CB750F. When starting the engine, there is a knocking sound coming from the center of the engine - in the area near the starter motor mounting bolts. On inspection, it appears that the Primary Gear Chain Tensioner is worn. I could not find a new tensioner and the part is no longer available through Honda. I then reassembled the engine - correctly to spec. Upon starting up again the noise has increased. If you rev the engine, the noise goes away at about 2000 RPM. To my mind, it seams like the increased RPM increases the oil pressure and thereby increases the Primary Chain Tension. Or am I wrong in my diagnosis? Any idea where I can get a new Primary Chain Tensioner?