Mechanical knocks. Mechanical knocks are noises that result from wear or improper adjustments. These knocks are not always easy to locate accurately as no two engines have exactly the same sound with the same faulty condition. Experience and practice are required on the particular type of engine to be serviced. The first step is to be sure that the noise is in the engine. If the noise can be heard with the vehicle stopped and the clutch disengaged, the . fault is generally in the engine. The engine should be warmed up to operating temperature. Check to see that all cylinders are firing, then try the engine under load to bring out the knock. Eliminate first such possible causes as carbon and valves, and then check for the following:  Crankshaft and bearing knocks. A heavy dull knock, most noticeable when the engine is accelerated under load, usually indicates loose bearings. This knock can generally be located by shorting out the cylinders on both sides of the loose bearing. End play is usually indicated by an intermittent knock which may disappear when slight pressure is put on the clutch pedal.  Piston and connecting rod knocks. Knocks caused by a loose connecting-rod bearing can be shorted out. The slapping noise caused by a loose piston pin is most noticeable when the engine is cold; it too can generally be shorted out. The noise caused by a broken piston pin or ring usually has a sharp clicking sound and cannot be shorted out.  Camshaft knocks. These knocks generally occur when the engine is going at half speed. The gear cover should be removed, and any play in the gears and shaft should be checked. Valve lifters and cam followers should also be checked.  Timing – gear noises. A humming noise may indicate tight gears. Loose gears and other timing gear faults are often indicated by a rattle or knock.  Valve mechanism knocks. If valve-mechanism knocks cannot be eliminated by valve-clearance adjustment, remove the mechanism and check all parts.  Water pump knocks. If knocks definitely point to the water pump, remove the assembly and repair or replace (par 98).  Other engine noises. Check such possible sources of other noises as loose fan blades, the air compressor (par 287), the engine mounting (par 219) and rnuff1er parts (par 87). This is an excerpt from Automotive Trouble Shooting For WW2 Vehicles, Volume 1 (paragraphs refer to this volume and to Volume 2. Both volumes contain a wealth of WW2 knowledge that are pertinent to ALL WW2 wheeled vehicles.