Figure 2-51. Ignition Timing
piston as a baseline. This Is the top dead center
In view A, the spark occurs at 10 degrees before
position that ends the compression stroke and
top dead center. In view B, the spark occurs at top
begins the power stroke (the top dead center
dead center. In view C, the spark occurs at 10
position that ends the exhaust stroke and begins
degrees after top dead center.
c. Effect of Increasing Ignition Timing (Fig.
the Intake stroke has nothing to do with ignition
2-52). After looking at the basic operation of a
timing). Any piston position that Is before top
dead center is referred to as btdc. Any piston
gasoline engine, it seems reasonable to assume
position that is after top dead center is referred to
that the engine will run fine if the spark occurs
as atdc. The positions are then further defined by
when the piston is at top dead center. In reality
giving the exact degree position of the crankshaft.
Figure 2-52. 2-33