Chevrolet Loose or Worn Bearings
This is only for Chevrolet Antique Cars
A bearing knock or thump can be detected in two ways: First, by accelerating the motor quickly, at which time a rattling and clashing sound will be produced; and, second, by starting the car with the brakes set, which will cause the motor to pull against resistance.By holding one end of a screw driver or rod to the ear and placing the other end at different points on the motor, the particular spot where the noise is loudest can be determined.
If the sound is loudest at the top of the motor, short circuit the spark plug on that cylinder.If the noise disappears you have located the cylinder in which the trouble lies.
The next step is to determine: First, whether it is due to a worn piston pin; second, to a worn or loose piston.
Worn piston pins can not always be located by short circuiting the spark plug, but by holding open an exhaust valve thereby reducing the vacuum in the combustion chamber on the suction stroke of the piston the knock will usually disappear, indicating the cylinder in which the trouble lies.
If the motor is cold, run long enough to thoroughly heat up the pistons and cylinder walls as a cold motor will always be noisy and is likely to deceive the inexperienced mechanic.
If the noise is produced by a loose piston, retarding the spark will lessen it however, the best test is to operate the car at a speed of ten to twelve miles per hour, either on a slight grade or by having the brakes partly set. Under these conditions a knock produced by a loose piston usually develops, and by short-circuiting the spark plugs, the cylinders containing worn or loose pistons can usually be located.
If the noise appears to come from the lower part of the motor, determine whether it is in the main crankshaft bearings or connecting-rod bearings.By holding the screwdriver or rod opposite the main bearings and putting the motor on a “pull,” the location can usually be determined with accuracy.
Remove the lower crankcase and tighten the bearings.
Worn or improperly adjusted push rods and valve lifters.
This is easily detected and adjustment or replacement made as per instruction.
Loose fly wheels bolts.This sometimes is a very difficult noise to locate as the sound is transmitted to all parts of the motor and gives the impression of loose main bearings.If tightening the bearings does not remove the noise examine the flywheel bolts.
Worn camshaft bearings or loose timing gear keys.
This noise can be located readily, as the sound will appear to be in the timing gear case.By slipping a knife blade between the valve stem and valve rocker arm, tension will be placed on the loose part, causing the noise to disappear. Remove the timing gear case and examine the crankshaft gear key.If this is in good condition the trouble is due to loose camshaft bearings.
Chevrolet Loose or Worn Bearings Article Source – This article courtesy should goes to : Chevrolet Repair Guide of 1923 by Chevrolet Motor Company.