In last month's Driving Old Cars, I covered Zoning an Engine to help in identifying and analyzing engine noises. This is done by dividing the engine into five zones: 1. Head 2. Block 3. Crankcase 4. Front 5. Rear, then using an engine stethoscope to listen to the noises coming from each zone. Being able to simply identify these noises is a help when we are away from our shops and diagnostic equipment. Whether contemplating buying a car at a car show, or having a breakdown while touring, scoping an engine sound correctly can save time and lots of money!
Most sounds are common to all engines if you know what to listen for. Last month we ended with main bearing noises
This month, we continue with
Crankshaft End Play: Excessive end play allows the crankshaft to float endwise, creating an irregular knock. The sound is similar to a loose main bearing. This does vary with different engines, and you can not short this noise out, but you can make it disappear by forcing the crankshaft endwise. Also, the intensity of the knock is only slightly affected by load. When building an engine, always check your manual to correctly set end play. An old mechanic friend of mine told me that many Buick Dynaflow transmissions' front pumps were pounded out due to excessive end play on the 322' s. It' s crucial!
Flywheel: This produces a knock with a slight metallic ring. It is loudest when the engine is revved, and seems to move through the engine, and can easily be confused with a bad rod bearing. It can vary in sound from a thump with vibration, to a continuous rattle.
Rod Bearing: A burnt bearing can be heard at all speeds, but is most prevalent at around 25 mph. Sounds range from a light pound to a series of short, sharp pops. It is not always heard at an idle, but is heard best with no load on the engine at part throttle. On this, you can short out the cylinder, and it can be heard on deceleration after revving the engine. It is lighter in tone in comparison with a main bearing knock.
Connecting Rod: Noises usually result from being bent, twisted, or not correctly lined up with the crankshaft and cylinder bore. It is usually heard at idling, or around 10-15 mph, and sounds similar to piston slap, with a slightly sharper tone. The tone can be somewhat diminished by shorting out, but the sound will not be eliminated. If left alone, it will eventually cause the rod bearing to wear, producing a rod bearing knock.
Piston: A worn or loose piston knock will usually be heard at an idle, on acceleration, and a higher speeds. This is called piston slap,and can be heard best using a stethoscope at idle. Of course, the degree of looseness affects the sound it produces. Generally, the knock is a hollow, bell-like sound, sometimes reaching a severe clanking sound when accelerating. At low engine speeds, it can click like a valve tap. With the engine warm, it can be checked by shorting out the cylinder. If the knock is from piston slap, shorting out will usually cause the knock to entirely disappear. Another test is to put a heavy oil in the cylinder, filling the clearance space. This usually will stop the slap for a few minutes. In a straight eight engine, the noise is loudest when the engine is cold, and lessens as the engine warms, although it can still be heard. If the piston is broken or cracked, the knock is present at all speeds and is loudest at idle and low speeds. At high speeds, it produces a heavy pounding.
Piston Pin: This sound is not limited to, but is best heard at idling. By retarding the spark, you can make it less audible. This is a dull, metallic sound, although high pitched, and not very loud. The intensity is less under load, and under quick acceleration. Shorting the cylinder will confine this knock to the upper part of the cylinder. If compression is relieved, the knock will usually go away. If the piston pin is at fault, the knock will always synchronize with the power impulse stroke of the piston.
Piston Ring: The cause of ring noise may vary from being too loose in the grooves, to broken rings, to hitting a ridge in the cylinder. A tone at regular intervals with the cylinder shorted, is usually a light, rapping sound or a clicking, or a sharp rattle. The noise created by a broken ring depends on the location of the break, and the amount of looseness in the groove. A loose fit with regular piston movement would produce a distinct rattling sound. A broken ring permits excessive blow-by and this can be checked by placing a rubber hose at the end of the breather and listening at the end of the hose.
Front End Noise: On chain-driven cars, there can be several factors causing the noise; 1. The chain might be improperly adjusted for tension; 2. The chain might be worn; 3. Sprocket teeth might be worn; 4. Sprockets might be loose or out of alignment. The chain must also be getting correct lubrication. Front end noise is usually a rumbling sound, due to too much slack in the chain. It is mostly heard at idling, or under acceleration. When the chain is too tight, you will hear a humming sound. To correctly adjust the chain tension, tighten it until you hear the humming sound, then back it off until it disappears. As the chain wears on engines with limited clearance, it may strike the housing, making a clanking sound at regular intervals.
Camshaft: Camshaft noise may be caused by excessive bearing clearance or end play. A loose shaft will produce a dull thump, sharper than a main bearing knock. A loose front bearing might produce a noise in the front end drive on straight eight engines. A loose cam bearing can be located by listening to determine the approximate location and applying downward pressure on the push rods riding the cams on each side of the suspect bearing. Usually when one bearing is loose, the push rods riding the cam on either side of the bearing will also be noisy. Depending on the type of engine you have, the tone of the noise may vary, but generally it is a sharp rap that usually occurs one or more times during a revolution of the camshaft.
Push Rods: Push Rod noise is usually accompanied by loss of engine power, and is caused by too much clearance between the valve stem and the push rod. With the roller type, it may also be caused by a worn roller or pin. It is a taping or sharp metallic knock, becoming a rap when the parts are worn. The noise is heard at regular intervals at camshaft speed. Excessive clearance can be temporarily taken up using a feeler gauge held between the valve stem and push rod. If clearance is decreased by a noisy valve, it will result in a popping in the carburetor. A valve with too much clearance will quiet upon taking up the excessive clearance.
Valves:Valve noise may come from several factors. Bent valve stems can produce a drum-like knock, sometimes accompanied by a pop, causing the valve to stick in its guide. This hollow, drum-like knock with popping in the carburetor is most noticeable under acceleration, but can also be heard at an idle. This can also be the result of a late-closing valve. Worn guides usually cause clicks and rattles, plus carburetor popping. Shorting out will not eliminate this noise, but will diminish it. Valve noise is generally heard at all speeds, especially under load when the engine is accelerating. A weak or broken valve spring can also produce a light knocking sound at idle and up to around 40 mph. Engine performance will be irregular, and the engine will usually backfire, especially at higher speeds. A broken valve spring can easily be seen upon inspection. To check for spring fatigue, insert a screw driver between the spring coils to increase tension and see if the sound changes. A jingling noise is associated with a broken inner spring.
I hope this helps in a quick check of internal engine noises. Watch for further articles on external noises (generator, fuel pump, etc.). During tough times, it is more important than ever to try and keep it simple! Enjoy your cars and support our vendors. Happy Thanksgiving from all of us at Southern Wheels Magazine. Keep ' em driving!