ok i have a 1990 (i think, i know it's early 90's or maybe late 80's) it has the 540 single cyl gas motor. it has a knocking sound when running. first i removed engine and removed side cover and i found the counter balance shaft was worn, i got a new shaft and installed it. the bushing in the weight measured within specs so i didnt replace that. while i had it apart i also checked the connecting arms for the weight and both are within specs big end and small end. i also checked the connecting rod and it is within specs. i checked the crankshaft bearing surfaces and both sides are within specs also the crank bearing surfaces are within specs. so i put it back together and install motor in frame and started it up and it is still knocking. what the heck would be causing it??????? i know the trans is not connected to the actual motor even though they share the same housing (yea motor and trans are 1 piece on these stupid motors) so the trans will only move through the belt and i have the belt off and also have the clutch off so nothing in the trans is moving. so tell me what else moves that will cause a knocking sound because everything inside checked out good. and the knocking sound is a loud knock just like a connecting rod would make but that thing is all good.