BUCKJUMPING

Shannon News, 4 May 1928, Page 4

BUCKJUMPING

CAUSES OF UNEVEN RUNNING.

PARTS THAT MAY BE AT FAULT

The way to find the cause of uneven running- in an engine is a subject which lias been cpvered many times before, but it is to be feared that there are still many motorists who are quite at a loss as to how to proceed when their engines commence to behave in an erratic manner. A skilled mechanic can often guess with some degree of accuracy the particular unit which is at fault, but the motorist with little past experience to go upon , will find it best to examine each part in a systematic way until the engine fires evenly again.

As the spark plugs are the easiest parts to get at, a start should be made with these, each plug being tested in turn with a screwdriver in the well-known way until the miss has been located definitely in one cylinder. To determine whether or not it is the plug which is faulty, remove it and exchange it with that in another cylinder, and if the missing is transferred to this cylinder, it is obvious at once that the plug is the culprit. If when cleaned and adjusted properly the cylinder in which it is inserted still refuses to fire, the plug should be replaced with a new one. On jhe other hand if the missing occurs in one cylinder all the time, no matter how the spark plugs are changed about, it is necessary to look elsewhere and suspicion should be transferred to the valve tappets, fOr it is quito likely that one of these is l adjusted so that there is no clearance between it and the valve stem, so that when the stem expands owing to the heat of the engine, the head is; raised slightly from its seat. This is- a fault which Occurs frequently within a week or two after the valves have been re-ground, and is caused by the valves settling slightly in their seats.

In one car which was troubled recently with uneven running,, it was found that no fewer than four tappets out of the eight were adjusted too closely. This condition, it is worth noting, is frequently accompanied by explosions in the silencer when the car is< driving the engine on a down in'g in its guide; this can be rectified grade. It is also by no means uncommon to find that one of the valves is sticksdmetimes by squirting kerosene round f the stem, but oftentimes the only cure is to remove the valve and clean it.

The next unit requiring attention is the make-and-break mechanism of the ignition system. This must be removed, and it* should be ascertained that the rocker arm is moving freely. The platinum points must then be examined carefully and if they are blackened or pitted will require dressing with a fine file made for the purpose, which is obtainable from | any garage or accessory store. In doing this one must use some care for it is necessary to make both faces level and parallel. However a 75per cent, contact will be quite sufficient.

Last of all, the carburetter adjust ments must be checked, and if there are any moving parts in the instrument such as automatic air valves one should make sure that these move freely.

There are, of course, quite a number of other things which can give rise to erratic running, particularly in the ignition system and carburetter but such faults will probably demand export attention for their rectification, and if, when the motorist has exhausted the methods given above, the engine persists in misbehaving, he is a wise man if he hands the car over to a skilled mechanic.