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having one of the secondary leads grounded as is common practice. One secondary terminal goes to the insulated terminal of one spark plug while the other is joined in a similar manner to the other member. The primary winding is just the same as employed for the usual form of induction coil. Every time the contact is established at the timer and the spark coil brought into action the secondary current is forced to leap two gaps instead of one and a spark is produced at each plug at practically the same instant.

Q. What are the advantages of this method ?

A. On engines of the T head form which have large combustion chambers it is claimed that the two point ignition system will result in more energetic ignition because combustion is more rapid due to the compressed charge having been fired at two different points. The advantages of this system are not apparent at low or moderate engine speeds but at high speeds Fig. 111.- Double Distributor Magneto, it is claimed that a 20%

Utilized for Two-Point Ignition System. increase of power is obtained over the single spark ignition system.

Q. What special apparatus is needed for two point ignition?

A. Either the spark coil or the spark plugs must differ from conventional construction in order to obtain two point ignition. If spark plugs of the conventional type are used as shown at Fig. 110 the induction coil must have two secondary terminals for each unit and the secondary current cannot be grounded, as is the conventional practice. If the regular form of spark coil is used having a grounded secondary terminal it is necessary to employ a special form of spark plug in connection with one of a regular pattern in each cylinder. A special two-point plug having two insulated electrodes passing through the insulating member must be used instead of the conventional pattern and this is introduced in the secondary circuit so that it is in series with the spark plug of the regular pattern used in conjunction with it. The spark must jump the gap at the two point plug before it can reach the gap between the electrodes of the regular pattern plug.

[graphic]

Q. Can two point ig nition be obtained when magnetos are used ?

A. A special form of magneto is necessary to obtain two-point ignition and use magneto current. A device of this kind is illustrated at Fig. 111 and it differs from the conventional construction, inasmuch as it has two secondary distributors and practically two separate windings on the magneto armature if

it is a true high tenFig. 112.-Showing Utility of Insulated Ter- sion type. If used in

minal to Test Current Flow to Spark connection with a transPlugs.

former coil system a four terminal coil will be needed instead of the usual form and each of the secondary leads connected to its respective distributor. One contact breaker serves both distributors on either the true high tension or transformer coil forms.

Q. How can current flow to plugs be tested with magneto system?

A. The current delivery to the ignition plugs can be easily ascertained when a magneto is used by an insulated terminal such as outlined at Fig. 112. When it is suspected that a plug is not firing it is possible to remove the terminal from the plug without danger of electrical shock and then by holding the terminal away from the plug electrode an eighth of an inch it is possible to see the current jump the air gap and thus determine if the electricity reaches the spark plug. If a spark jumps between the terminals and the plugs and the cylinder does not fire it s reasonable to assume that the plug is dirty and that the trouble is not with the magneto. If no spark jumps between the terminal and the plug it indicates either a broken or grounded wire or a defective contact at the distributor.

LESSON TWELVE

METHODS OF LUBRICATING THE AUTOMOBILE

POWER PLANT

Q. What is lubrication?

A. Lubrication consists of interposing between two surfaces that have relatively great friction, a cushioning and almost frictionless medium that will separate these surfaces and enable the parts to move with expenditure of less power.

Q. Why is lubrication necessary?

A. If the moving parts of machines which work on or by each other and which are in frictional contact were not separated by a film of lubricating oil or grease the metallic contact would result in abrading the surfaces and producing rapid depreciation. In some parts enough friction might exist to cause the pieces in contact to become so hot that they would seize together. This would be very liable to occur in high speed bearings or in bearings subjected to heavy pressure.

Q. What is friction?

A. Friction is the retarding force that tends to prevent movement of all mechanism which is in motion. The friction may result from internal or external forces and it is exerted in such a way as to bring all moving parts to rest. Friction is generally caused by the interlocking of minute projecting particles which extend from the surfaces of all substances regardless of their nature or the accuracy of surface finish. Friction is greater between soft materials than it is between hard substances and the rougher the surfaces in contact the greater will be the amount of friction between them. It requires power to overcome friction in all cases and the greater the amount of friction present the more power is needed to overcome it.

Q. Should friction be eliminated in all parts of automobiles?

A. Some parts of motor cars perform work where friction is necessary to enable them to function properly while other parts will work more efficiently as the amount of friction is reduced. For instance, it is necessary to have friction between the parts of the clutch used to transmit power from the engine to the gearset and it is necessary to have friction between the brakes and the brake drums when these members are applied to stop motion of the car. If there was no friction between the tires of the driving wheels or traction members and the ground it would be impossible for the power plant to propel the car. At the other hand if there was too much friction at the bearing points of the motor, gearset, power transmission parts and wheels, it would be practically impossible to propel the car without using large quantities of power. It is important that friction be eliminated or reduced to as low a point as possible at all bearing points in order to obtain efficient power generation and transmission. The more friction there is in clutches and brakes he more efficient these members are.

Q. Name the principal lubricants and their derivation.

A. The principal lubricating mediums commonly used to separate the parts of machinery in motion are fluid oils and semifluid and solid greases derived from mineral and animal sources. Solids, such as graphite, which is a form of amorphous carbon, are also used for lubricating purposes.

Q. Are all lubricants suitable for the same parts?

A. The lubricating mediums best adapted differ with the nature of the work the parts are to perform. An oil that is suitable for one portion of the automobile mechanism may prove actually injurious to other parts.

Q. Name the conditions where oil can be used ?

A. Oils are the only lubricants that can be successfully employed in lubricating automobile power plants. Oil is necessary wherever the amount of space for the film of lubricant is small or where considerable heat is present.

Q. Name conditions where only greases can be utilized.
A. In certain parts of the power transmission system such as in

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