Understanding how a car works and identifying what it's telling you brings peace and confidence in driving old cars. As much as I love using all of the latest tools and diagnostic equipment, there's something very satisfying about listening to your engine with a stethoscope and nailing the problem. The purpose of this article is to set up an orderly approach, from the simplest to the worst-case-scenario, to solving many engine problems by process of elimination. Most of our old cars are non-computer, and this is the way the old-time mechanics did it, using their five senses: Sight, Smell, Hearing, Taste and Touch, as well as a sixth--Common Sense! It is important to focus on the main problem, but to be aware of everything around it at the same time.
I remember one time we were working on our '46 Packard 356 Straight 8. The car had been in storage for several years, and everything needed servicing. One man was under the hood listening to the squeal of the water pump. I was behind the wheel, and had to re-start the engine several times when finally the starter hung up. The Bendix didn't kick out, and before I could get out of the car, the starter had caught fire! The guy under the hood was still listening to the water pump squeal, oblivious to the fire. Using the battery quick disconnect, I was able to arrest the problem, only losing a $600 starter and not the entire engine, car and garage! You have to use all of your senses and be aware of your entire work area.
When we are scoping out a noise, we consider the whole engine, but divide it into zones: Zone 1-HEAD; Zone 2-BLOCK; Zone 3-CRANK CASE; Zone 4-FRONT; and Zone 5-REAR. Then, using a stethoscope, listen to each zone to help narrow down the problem. Once, while working on our ' 49 Buick 320 Sedanet, we heard a light rapping coming from the head area. We had just done a valve job, and knew everything was right, but what was that noise? We moved the stethoscope around, stopping on a loose bolt that held the spark plug cover plate on. Once it was tightened down, the noise was gone. It had sounded like a rod bearing or loose valve. The noise even increased when the engine was revved, but it was just a loose bolt! Sometimes you get a break!
After setting up our zones, we make a list of what the possibilities could be. For example, General Problems--Carbon, Detonation, Spark Knock, etc.
HEAD: Bad valve guides, sticking valves, out-of-adjustment valves, broken or weak valve springs, ridge worn on valve seat or work push rods, excessive camshaft end play or worn bearings. With the modern oils, and the elimination of ZDDP, camshaft lobes are beginning to show premature failure, especially in the high-revving engines.
BLOCK: Worn bores, loose pistons or rings, rings stuck, a ridge in the cylinder, piston pin loose (this one can be hard to identify--we had one that sounded like a valve out of adjustment).
CRANK CASE: Crankshaft main bearings loose, excessive end play, shaft out of alignment, bad connecting rods or bearings, bent rod.
FRONT of the engine: There could be worn gears or chain, end play, broken bolt in the harmonic balancer (we had this on our ' 54 Cadillac 331 and it could be heard through the radiator, sounding like a bad rod bearing), cracked harmonic balancer, fan belt or fan, also check generator and water pump.
REAR of engine: Crankshaft end play, flywheel, or starter. To begin testing, if it' s at all possible, have it timed and firing on all cylinders, and warmed up to operating temperature. It is also helpful to try different RPM' s to see if the noise changes.
LET11 S START TESTING! Detonation which is commonly known as fuel spark or compression knock, is really incomplete combustion. The sound is a sharp knock with a metallic ping, heard especially when the engine is under a heavy pull, or accelerating in high gear. The sound of the knock will change when carbon builds up, when mixture is too rich, when the timing is off, or if the fuel is too low in octane for the engine's high compression. It can also result from a lean carburetor adjustment.
Carbon makes an erratic knock that shows up on a hot engine, and is called pre-ignition. The sound becomes more pronounced as the spark is advanced. It also changes with carburetor adjustment. It is similar in sound to Detonation and is loudest under heavy engine pull or acceleration. The difference comes when retarding the spark changes the tone and may make it go away altogether. The engine will always lose power.
Spark Knock also produces a pinging sound. It can be caused by a faulty vacuum advance, an overheated engine, faulty ignition wiring short-circuiting, or too hot of spark plugs.
Cylinder wall problems can make a ' hissing' sound in the crank case on the compression stroke. This also can be evident by a loss of power, and crank case breather smoke. It almost always indicates scored cylinder walls when new plugs are put in an engine where the cylinders have not been reconditioned and have ridges, and new rings. Besides making the hissing noise, which results from loss of compression, the new rings might break on the ridges during ring travel.
Cylinder Head: Water in the oil pan can be the result of a cracked of loose cylinder head. It can also be caused by a bad head gasket. As the compression is lost, it produces a hissing sound, along with loss of power. Many times the coolant can be seen seeping out around the head gasket.
Main Bearing Knock : You can hear and feel this one. It's a dull, heavy knock that can be felt with your foot on the accelerator, always louder under a load. When the bearings are about to go, it can be felt and heard at an idle, but generally is most dominant at 25-30 mph. The knock is usually periodic, because of unequal wear on the main bearing. A single knock can indicate a single bad bearing, and might show up at a certain speed, go away, then show up again at a higher speed, producing a deeper tone. Know how many main bearings your engine has. Loose main bearing knocks, especially the center one, can be diagnosed by the way it sounds and the tone it produces. When all mains are loose, the tone of the knock will remain the same, but the timing of the knock may vary, depending on the number of main bearings, as the number of knocks per revolution depends on this number. To isolate the bad bearings, shorting out the cylinders adjacent to the bad bearing will quiet the noise.
We will continue next month with Part Two. Enjoy your cars and keep 'em driving!