THE IGNITION POINTS

CHECKING THE FLYWHEEL KEY

Once the flywheel is free of its fit on the tapered portion of the crankshaft, try to move it clockwise and counterclockwise without turning the crank. If it moves even a few thousandths of an inch, check the half-moon key that positions it on the flywheel and the recesses into which the key fits (S-16). Normally the wear occurs in the key, and a new key is an in expensive piece of insurance if you have any doubt. If the new key fits sloppily in the flywheel, the flywheel must be replaced. If it fits loosely in the crankshaft, the engine may require overhaul, and you might consider a replacement engine, as discussed in Chapter 9.

 THE IGNITION POINTS

Once the flywheel is off , you’ll see the ignition points or the sheet metal or plastic cover under which the points are located. The points and condenser setup looks very much like that in a pre-1975 automobile arrangement; but there are a number of differences, both in operation and service. See 6-18.

In the automobile, the points and condenser are housed in a distributor, which also has the job of transmitting spark to the correct plug. With a one-cylinder small gas engine, there’s only one correct plug, so there are fewer parts.

Whether the engine is a two-cycle or a four-cycle, the points are opened and closed by the crankshaft in all but a few four-cycle engines, such as the Briggs MagnaMatic, in which the points are opeated by the camshaft (as in the automobile)

A small lobe on the crankshaft (or camshaft) pushes one of the breaker points away from the other, which is fixed in position. The push may be direct, or indirect. In the indirect setup, the crank lobe pushes on a short rod called a plunger, which pushes on the movable point. As the crank continues to turn, the lobe releases pressure and a leaf spring brings the movable point back into contact with the fixed point. See 6-18 and 21.

The gap between the two points when the lobe is at the maximum push position is extremely important. If the gap is too small, current can arc across it, and the break in the circuit that is necessary to create the spark will not occur. If the gap is too great, the points will open a bit earlier than they should and close a bit later.

This can have two consequences: Inas much as the opening of the points results in the spark, the plug will fire too early, reducing performance. Or the late closing of the points may reduce the electrical charge absorbed by the magneto coil, weakening the resulting spark.