A big part of the Driving Old Cars experience is to have the car running right! If it's a V-8, when you punch it, you want it to go. If it's a straight 8, you want it to run smooth and quiet. Foreign noises disturb the experience. Many times, a noise can be external and mimic an internal noise. As I mentioned in a previous article, after a tune up on our '49 Buick Roadmaster 320, we put the spark plug cover plate on, and one of the nuts was left a little loose. When the engine was warm, the cover plate didn't rattle, but when we started it cold, it made a rapping sound like a bad rod bearing. We tightened the nut down and the sound went away.
Once when working on our '58 Buick 364, the car had been sitting for 5 or 6 months. When we started it, there was a bad bearing-type of sound that seemed to be coming from the water pump. With a motor scope, I listened to the water pump, then the generator (running on the same belt). It was louder at the generator. A few drops of oil in the oiler hole of the generator quieted it down, then the sound went away entirely. I could have replaced the water pump and still had the noise. Spending time isolating the sound and being aware of telegraphing noise from one part to another can save time and money.
The most obvious external noise besides brackets, covers, etc., generally come from the fan and belt, generator/alternator, starter, carburetor, fuel pump, lubrication system and vibration damper.
FAN NOISE usually has a clicking or rattle at operating speed. A fan blade may be bent and hitting (check for a bright spot on the water pump or close-by surface where the fan would hit). If it is a ball bearing fan, check for a bad bearing. This will produce a clicking sound. A loose fan might produce a rattle. Some aftermarket 6-blade fans can produce a whirl or humming sound. If the fan belt is too tight or too loose, it might produce a squealing sound. When you change fan belt styles, be aware that a corrugated belt might sound differently from a standard belt. The belts notches are like gear teeth, trapping air in the spaces between the pulley and the notch. If the corrugated belt is chamfered on its edges, it will eliminate any noise by letting the air escape.
GENERATOR: If the armature does not rotate freely, it might produce a noise, possibly from bad bearings or a bent shaft. This usually shows up as scores on the core of the armature. Loose brushes might cause thrown windings on the armature. Bearing bind usually causes a squeal. If the generator/alternator belt is too tight, or the brushes are bad, this might also produce a squeal. If the bearings are bad, that usually shows up as a grating sound. Sometimes you can get lucky and there can just be dirt or grit on the bearing, and not actual bearing wear. A knocking sound might result from too much end play.
STARTER: A noisy starter has similar symptoms as the generator. Gear reduction starters will be noisy if gear teeth are broken. If the starter is not in alignment with the flywheel, the gears will clash, producing a rasping sound. The gears of the starter drive must also have proper backlash. If the pinion rides too high on the flywheel teeth, a meshing sound will result when starting.
CARBURETOR: It is normal for a carburetor to make a hissing sound that increases when it is throttled. For backfiring, fuel intake and quantity should be checked, as well as timing, ignition system, air leaks and valves. Always check your air cleaner for clogs and obstructions. A dirty air cleaner may produce a rich-running engine, creating a rumbling noise from an open exhaust. A loose air cleaner or bracket can produce a rattling noise.
FUEL PUMP: My favorite fuel pump story is from my good friend Ron Carpenter. He was once working on a '41 Packard that used the fuel pump mounting bolt bushings. They had been left off of the car, and the fuel pump was vibrating on the mounting bolts that produced a rod-knocking sound. When Ron installed new bushings (he makes them), the noise disappeared! Sometimes you get a break.
There are, of course, more serious noises, such as a broken rocker arm spring, bent rocker arm, rocker arm binding on the shaft, or anything that would keep the pump from running on the camshaft. On combination fuel/vacuum pumps, check for all pump part clearances. The pump will be noisy if the rocker arm pin is worn, the fuel pump link is striking the upper diaphragm protector, or the vacuum pump diaphragm spring is rubbing on the fiber bushing. Insufficient fuel pressure is almost always associated with the above problems.
LUBRICATING SYSTEM: Noise in this system can be caused by too high of oil pressure or oil starvation. I remember once we were working on our '46 Packard 282 cid. We had completely disassembled the engine, put in new rings, did a valve job, pressure-washed out the block: We thought it was clean. After we put it back together, we switched from 30-weight, non-detergent oil to 30-weight detergent oil. After test-running the engine, then starting and stopping it a few times, it started to squeal. We shut it off, but not before taking out #5 rod bearing. The detergent oil had done its job and cleaned out what we had missed. When we removed the oil pan, sludge was all up into the oil screen. Ill never do that again! Unless the engine comes out of the car and is oven-baked, Im sticking with the oil it was born with.
Other noises might be heard from a failing oil pump, which will usually show low oil pressure. A restriction of the connecting rod oil passages might create a knock like a bad piston pin or push rod.
VIBRATION DAMPER: Once on a '54 Cadillac, we heard a noise coming from the front of the engine. It sounded like a rod bearing noise. It turned out to be a cracked damper. A bad damper can also produce a vibration. When rebuilding your engine, its always a good idea to have the damper rebuilt (we use the Damper Doctor, in this magazine).
There are other miscellaneous noises: Loose manifold heat control valves can produce a rattle or knock similar to a bad piston pin. A stuck-closed heat riser can overheat an engine, causing it to rumble when shut off.
Being able to find and diagnose these sounds gives confidence and independence to the owner, making Driving Old Cars fun! See you next month, and keep em driving!