OMC Stern Drives And Motors 1964-1986 Repair Manual., Page 43Get this manual
ENGINE SERVICE
GMC IN-LINE ENGINES
A new generation of engines has been developed with various 153, 181, and 250c as follows: the 153-18 CID engines four-cylinder powerplantsT 250 has six cylindersT four-cylinder engine has four main bearings, while the six-cylinder engine has sevenThese engines have many interchangeable parts, because most have of 3.875" and of 3.25"T 181 unit has larger bore of 4.000" and of 3.60tt, while the 250 engine has of 353"All center-to-center bore spacing of 4.40"Standard numbering of the cylinders from the of the engineT firing is standard, 1-5-3-6-2-4 6cylinder engines, and 1-3-4-2 for the 4cylinder unitT following service sections coded assist you in referring particular section quickly when performing the workYou will find the numbers referenced in the chapters
will be loudest when the engine decelerating,Piston pin noise and piston slap generally louder when cold engine is startedMany the source of unusual sound may be isolated by using stethoscope the listening deviceO such device isshank screwdriverAllow your hand extend over the end of the handle, press your hand, and the probe with the other end of the screwdriver by touching it firmly against the block cylinder noise areaT and use good judgment when using this method of the cause of problem because the noise will travel through other metallic parts of the engine and could lead false interpretation of what you hearingCarbon build-up in the combustion chamber cause interference with ist tonFuel pumps can knock, belts can be noisy, distributors can clicking noises, and can unusual soundsFlywheels, pumps, and loose manifolds can also cause noise problems-