The Birmingham age-herald., 1919-10-05

AVA every l6NDluNAOu Ol ltlC VI and therefore any wear is shown up by pounding or knocking at each reversal. The whip of the nod tends to throw it from side to side and any iooseness which may exist will cause knocks
 Valves and tappets necessarily produce some noise. because sufficient clearance must be left between them to allow the valve to seat firmly. When this clear ness becomes excessive there is a stop at each lift, and with all of these work ing in rapid succession the noise is quite pronounced. With the overhead valve there is a greater possibility for looseness and side play with its resulting annoy ance. With slide and rotary valve mo- tors this is practically eliminated.
 Loose, crank and camshaft bearings will change the center distance between the timing gears, thus allowing these to mesh unevenly. Improper fitting of bearings in overhauling and adjusting will also cause this uneven meshing of gears. Bent shafts will also cause the same trouble.
 A hissing noise or whistling screech is produced occasionally when the gaskets under valve plugs, sylinder heads etc, are not tight. Spark plubs will cause the same sort of noise when the core breaks or becomes loose. Inlet and ex- haust manifolds will also cause missing, if loose, and in the case of the inlet, will also produce a loss of power. A loose priming or pet-cock acts similarly to broken spark plug core.
 A loose flywheel will also cause a sort of dull knock, which is not so mo- ticeable when the car is pulling, but becomes quite noticeable when the clutch is disengaged.
 HOW TO LOCATE MOTOR KNOCKS
 There are several methods of locating motor knocks; however, the most positive method is by the use of what may be called a listening rod or by the use of stethoscope. A long wooden handled screw driver forms a good listening rod. The flat end is placed against the cyl inder or crank wall and the handle to the ear. It will be necessary to try various locations until you come in close prox- unity of the knock, when it can be heard very distinctly. In some shops a special tool is provided for this purpose, made from piece of steel tubing with a wooden handle, and metal plug in the bottom. Detecting the knock is quite simple; how ever, it's actual location is a problem not so easily settled upon, and some prefer to use a stethoScope, as used by physf- clans in locating irregularities in the action of certain organs of the human body. It consists of a piece of hard rub Der connected by rubber tubes to the
 
 by placing the two branches in the ears, and the hard rubber. end is placed over the engine, the noise observed increasing as the location of the knock Is ap- preached. Only the sounds that are produced in the immediate vicinity of the point at which the instrument is applied are heard in the instrument.
 To determine whether a knock really exists, the engine can be run idle at va riOnS SnppnS and the iS driven smooth, isolated road The isolation pro- vides quiet surroundings, while the smooth pavement excludes all knocks and rattles of other chassis and body parts.
 HOW TO DISTINGUISH KNOCKS
 In the following paragraph the various motor knocks are described, together with the cause. In compiling these paragraphs we are endeavoring to make this infor- nation as clear as possible in order that the repairman may use this portion of the article as a trouble hooting chart for locating and diagnosing these intri- cate problems which arise daily, and which, as rule, are not generally under stood, unless one has become an expert in this line.
 MAIN BEARING
 This is usually detected by a hard bump being noticeable throughout the motor. It is caused by end play in the shaft, loose-fitting bearings, scored, seized or burnt-out bearings. Tn the lat ter cases the motor will groan upon start ing when cold On a three bearing, four cylinder crankshaft it is very often a simple matter to determine whether the end or center bearings are the ones pro- ducing the knock Since the center bear ing has a piston and connecting rod on back side of it. and the explosions in the two cylinders follow each other at equal intervals, there is a peculiar double knock, whereas on either of the end bearings knocks come singly and at equal time intervals. With a ball bearing crankshaft rumbling noise will exist if the races are clipped or the balls broken.