HELPING GARAGE MECHANICS

New Zealand Herald, Volume LXXIII, Issue 22344, 15 February 1936, Page 11 (Supplement)

HELPING GARAGE MECHANICS

Jf a car owner takes note of symptoms as and when they exhibit themselves before, after, or during the occurrence of an irregularity, he may facilitate the diagnosis and care of tho trouble by a motor mechanic, even though he may not recognise the fault himself while noting its symptoms.

The motorist who is unable to assist the mechanic in diagnosing the car's trouble will probably have a bigger bill to pay when the noise has been traced and cured, for the repairer may have to drive the car 20 or even 50 miles to identify and locate it. Admittedly, some irregular noises are very difficult to describe, and the circumstances in which they are prone to arise are not easy to recognise and recall. But before the car owner seeks the help of a repairer he should try to form some idea concerning any kind of fault, so that he can pass it on, in the hope that it will aid in diagnosis.

When an engine misfires, for example, the driver should be careful to note the running conditions, if any. that always or usually cause it to commence, cease or become less or more noticeable. He should notice whether a knock comes on when the engine is pulling or the car is over-running the engine, whether it occurs, continues or ceases when the car is coasting with the gears in neutral and whether it is louder or less evident as and when the engine warms up. Each of such symptoms may carry the mechanic a little or a long way toward quick and correct diagnosis. A bad squeak on all except very smooth roads was traced without delay on a car when the owner was able to tell a mechanic that it always ceased for a time after the car had been washed and soon after the car had been taken out on a wet day. The body-holding bolts were slightly loose, allowing the body to " jiggle " on the chassis; but when water got between the insecure* contact surfaces it served for a while as a lubricant and stopped the squeak. Among the symptoms of irregularities that should identify themselves to the motorist are the following cases:— When an engine misfires badly, practically ceasing to fire as soon as it attains a certain speed, irrespective of the gear in use, one is fairly safe in diagnosing a partially-choked petrol filter—petrol " starvation." If an engine has been pulling well and suddenly stops without warning, coil failure may be suspected on a car with battery ignition, particularly if the engine was running fast a moment before it ceased to fire. But if it would run at an idling speed and then stop when an attempt was made to accelerate it, a choked main jet would be a reasonable diagnosis. On the other hand, if pops and bangs accompanied the sudden stop, coil trouble could be ruled out at once; more likely the cause would be a

ffow Drivers Can Reduce Repair Bills DETECTION OF COMMO

" floating " impediment in the passage between the carburettor float chamber and jet.

When only one cylinder ceases to fire the cause will almost always be in tho ignition—a. cable adrift or a sparking plug at fault. But if all cylinders misfire regularly the contact-breaker is the first thing to inspect and test. Engiuo knocks can be divided into several classes —the light tapping, metallic knocking, heavy thuds and so on. Light tapping can be attributed to a loose gudgeon pin, loose pistons or slack rings; it may also emanate from the valve gear, or the camshaft, the timing gear, or may be an ordinary carbon knock, causing pinking. Dull thudding is usually due to a slack main bearing. Light thudding or clatter emanates from loose big-end bearings. Tappet clearance, if excessive, produces a regular tapping, which varies with the speed of the engine. This may be traceable to wear or to faulty adjustment.