1985 Mercury Outboard V-300 V-3.4L Shop Service Manual, Page 114Get this manual
Connecting Rods Chatter Marks: Chatte marks arc the result of combina tion of low speedlo loadcold water te mpera ture operationaggravated by inadequate lubricati on and or improper fueL Under th ese co ndit ionsthe crank shaft jo urnal is ha mme red by the connecting rod As ig nit ion occurs in th cylinderthe pisto pushes the connecting rod wilh tre mend ous fo rceand thi force is tra nsferred to Ih connecting rod journalSince th ere is litt le no load on th rankshaftit bounces away from th co nnecting rodTh cra nkshaft th en re mains immobile for split second un! il Ih piston travel cau ses th connecting rod to catch up to the wait ing ranks haft journalthen ha mmers it Th repet ition of this aclio causes rough beari ng surface (s) whi ch resembles tin washboa rd In some instances, th connecting rod rankpin bore becomes highl poli shed During ope ra tion, th engine will emitwh irrnd o "c hirp" sou nd wh en it is accclerated ra pidl from idle speed to approximatel 1500 RPMth en quic kl re lurned 10 idleIf Ih preceding conditions re fo undreplace bOlh Ihe cran kshafl and con necling rod (s)