Engine Noise Diagnosis   (John Myers – Vetteworks)

Here’s a real quick run down of engine noises and their possible causes. This has been put together through research and troubleshooting guides from numerous manufacturers. This will be updated continually...so stay tuned.

We’ll begin with the scariest first…

Rods
If your engine suddenly sounds like its gonna come apart…it probably will. This isn’t one of those sounds that you ignore, or hope will go away. Its there and it’s loud, like a gorilla beating on your block with a hammer. Sometimes the knock can be less severe which may be evidence of a failed journal bearing. In this case your rod may have lost its true-ness and is probably bouncing it’s way through each revolution of the crankshaft .

To Verify use a garden hose or a long screwdriver against your ear.    You may be able to detect exactly where the noise is coming from by holding them against the block at different locations. This trick works like magic. (Don’t forget to plug your opposite ear!) The only remedy here is the removal of the oil pan and investigating to see how extensive the damage has become.

Burned Valves
Your engine will definitely sound rough and won't benefit from a tune up. Backfiring in either direction of your intake or exhaust may also indicate a burnt valve.   Exhaust valves often fail long before the intake valve.  Still the possibility that the intake valve is damaged shouldn't be ignored.  Foreign objects like nuts, bolts, rags and so forth may have caused the problem.  In this case it could be any valve.  Ignoring it is a matter of choice and should be considered depending on the severity. 

Similarities exist with the sounds of a burnt valve when compared to a vacuum leak or bad compression (ie: Broken ring or hole in piston).  Make sure you know the difference.

To Verify Check the exhaust for a pulse by putting your hand over the exhaust and feeling for an uneven pulse or rhythm.  Be especially alert for any feeling of vacuum.  This can show up because of the open path past the exhaust valve during the intake stroke.  Another method you can use to determine this is by disconnecting the ignition coil and cranking over the engine.  As compression is lost in the affected cylinder, a momentary increase in speed of the starter can be heard. If you still can't 'nail it down' try disconnecting the spark plug wires at each cylinder. Do this until you notice that no change of idle quality results.  In other words, without that particular cylinder firing, there's no change in engine idle or sound.    Lastly, get yourself a compression tester and check each cylinder.

  Valvetrain Chatter

There are a number of things which can cause these symptoms to occur.  Normally, this  sounds like a metallic 'ticking' near the top end of the engine which decreases as the engine warms up.  In more severe cases it can be quite noticeable and may not go away completely.

In many cases this can be the hydraulic lifters.  Either they are out of adjustment or haven't had a chance to 'pump up' completely.  On the other hand it may be piston 'slap' (which may go away as the engine warms up), a small header or exhaust leak, a collapsed lifter, a flat cam lobe.  This sound may also be totally normal for a solid lifter camshaft.  If it is a collapsed lifter or deteriorated camshaft lobe, performance would also suffer.

To Verify use a garden hose or a long screwdriver against your ear.    You may be able to detect exactly where the noise is coming from by holding them against the block and heads in different locations.

To fix this it will probably require a rocker arm adjustment.  Verify that all rockers are 'rocking' equally.   Any  variation in rocker arm movement may be evidence of a defective camshaft.   Verify lift height after adjustment.  Also verify the free and unobstructed travel of all the components to include rocker arms, lifters, pushrods etc.

Exhaust leaks

Exhaust leaks can show up as a ticking sound, a noticeable 'ppffft ppffft' sound or a louder 'vrap, vrap, vrap' sound.   Sometimes an exhaust leak can be evidenced by backfiring.  In this case cool outside air is being sucked into the hot exhaust and mixed with residual fuel.  If hot enough it will ignite, causing a backfire.

To Verify You can use a screwdriver but the best method is to carefully feel for the leak around the exhaust manifold or header tube seams.  Also, you may be able to look for signs of black soot or trails of exhaust emanating from the leak.

To fix this you can opt for a new header gasket or copper RTV.  You may get away with a re-torque on the header bolts.  In some cases, a warped header flange may cause continual problems.   Some mechanics double up the header gaskets to remedy this.