Engine Noise Diagnosis
Diagnosing engine noises can be a difficult and imprecise art. When investigating engine sounds, try listening from different locations. Upon first hearing a running VW engine, the initial impression is a confusing combination of sounds.
Aids for isolating and locating noises are either a stethoscope, length of heater hose or a wooden dowel. Unlike a doctor's stethoscope, an automotive stethoscope has a solid metal probe at the business end. It works best when held against a solid part e.g. Cylinder head, Crankcase, Manifold, Bolt head etc. If a noise is suspected beneath a cover, place the stethoscope against a nearby bolt head or solid object. For example, a noisy valve is best heard by listening at the edge of the rocker cover or cylinder head, not at the middle of the rocker cover.
An alternative is to use a length of hose or dowel instead of a stethoscope. With a hose, hold one end firmly against the engine and the other end to your ear. When using a dowel, position the receiving end of the dowel against your skull, just forward of your ear, so engine vibrations will not bounce the dowel into your ear.
Engine noises can be divided into three categories:
The difficult part can be determining what these problems sound like. Initially identify the normal engine sounds.
Listening to an air-cooled VW, the dominant sound will be the exhaust. Leaning forward into the engine compartment will help mask the exhaust, in order to more easily hear internal engine noises. Once past the exhaust, the main noise of an idling engine should be the soft ticking of the valve train. If the engine rpm is raised above idle, the ticking should turn into a whirr. If one valve is heard over the rest, or if all the valves are making more of a harsh clacking sound, the valves require adjustment.