ENGINE TROUBLE.

Press, Volume LXI, Issue 18365, 24 April 1925, Page 5

ENGINE TROUBLE.

LOCATING BY NOISE. Each part of the engine makes a fairly distinctive uui-c v.-Jicn U starts to wear, but ii is ! ,l,s * i,)le h >' listening to 1 lie sound to Ml wlir,t l ,an this is. Any unusual noise about ori engine should be investigated a I once. 'Suppose you lot rhe.ti; li-v;-! '» e,:,n ' v " ease van toy lo.w or have tailed to keep the radiator tilled with wate<. L he engine wiii quickly start t" kii'".'k and lieal tip. warning >ou that something is wrong. if voir fail to lioed ilii.s warning, the next tiling you know ti.e enable .';: ops, and vcu are very iuckv iis■ i<_■ t :l >ou have' not burned out some coimei-ring rod bearings or scored the cylinder Avails.

The most common knock in an engine is "carbon knock,'' which causes it to make, a '••clinking" sound when pulling hard or when accelerating. Carbon knock is always worse after the engine is heated up, and can generally be stopped by retarding the spark lever. 'This is only a- temporary cure, and the carbon shouid be removed at, the first opportunity. Valve tappets adjusted with too much clearance make a 'light Lapping sound. When the engine is cold there will alwavs be a certain amount of noise from the valves, because a slight space

of clearance must be left between the valve stem ami tappet to allow for expansion when the engine heats up. When the engine is warm the valves siioul.l make practically no noise, nil you should hour is a soft purring sound. It you hear a noisy tap, or a series of taps, it shows that some of the valves require adjustment. Extreme care must he taken, however, to see that the valve tappets are not adjusted too often or the valves will remain partiy open all the time. In such a case the face of the valve seat will soon be burned, and the valve will have to be removed anil ground in. On the other hand if the valve clearance is not adjusted -close enough. . the engine will be very noisy;-ami will-have no pep. The clearance varies on different engines, and if you are not familiar with the operation of adjusting valve clearance, have it done by ,i mechanic who is "fiim'iliar with your make of car. . . ' ■ To locate which valve or valves arc noisy, hold the rocker arm or bush rod against the end of the valve stem while the engine is running, and notice whether it makes any difference in the sound. if you tinil the noise is reduced, when you hold up a certain trippet, then that is one of the valves that require adjustment. Connecting rod bearings, when worn at the little end, make a rapping sound like a hammer tapping on steel. When the engine is pulling hard or you are travelling at a fast speed, you will hardly notice any noise, but immediately you slow down on the level to about 20 miles an hour, or are coasting down a hill, worn connecting rod bearings will make a continuous rapping sound. To test for wear, insert the startinghandle and after switching, off the ignition, "see-saw" each cylinder against compression. If any of the bearings are worn you will both feel and hear them. : Make this test when the engine is warm. Worn "big-end" connecting rod. bearings make a loud knock. Worn -main crankshaft bearings make a dull thudding sound, especially when the engine is pulling hard. Unless they are worn badly you will not hear them at all when running on the level at a moderate speed. If you'notice a dull thud, thud, thud when climbing a hill

or when the engine is pulling hard, you can be fairly certain ■ that the-crank-shaft bearings require attention. hen the piston rings and pistons begin t () wear and the walls of the >..'•' indeis become worn, piston slap de-v*-:ops. This trouble is particularly noticeable just after the engine is started and is cold. When the piston slap is had you may be inclined to think that you have about a dozen old tin cans tossing about inside the engine, for this is just what piston slap sounds like. Sometimes new piston rings will cure the trouble, but it is generally necessary to have a set of oversize pistons aiid rings riTted. • hi extreme cases the cylinders may be worn oval, in which case they will have to be re-ground before the ne.w pistons are fitted.

When your engines start to knock suddenly, it is advisable to stop at once, and make sure that there is enough oil in the crankcase and water in the radiator. If" these are O.K. then test the cylinders to see that all are firing regularly. It is quite a common experience for a ear to be brought into the service station with what the owner Thinks is a knock in the engine, only to find out that all that is wrong is a fouled spark plug which has been onus: ing the engine to misfire. If you want to keep your engine . quiet and free from knocks, keep the oil in the crankcase at the correct level at all times, and use the correct grade of oil for your particular engine. In addition to this, drain off the old oil every 000 miles, and refill with fresh oil. ' After ~>oo miles the" oil is badly diluted with gasoline, and does not lubricate the engine properly, so causing rapid wear. • •

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