Tecumseh ECV100-120 - TECHNICIAN S Handbook page 69

The condenser acts as an electrical shock absorber to
prevent arcing between the contact points as they open.
Arcing will lower the voltage at the spark plug, as well as
burn and pit the contact points. The condenser is a
replaceable item (diag. 10).
The spark plug is made up of two electrodes. The outside
electrode is grounded and secured to the threaded sleeve.
The center electrode is insulated with porcelain. The two
are separated by an air gap which creates a resistance.
A large voltage from the secondary arcs the air gap which
causes a spark and ignites the air-fuel mixture in the
cylinder (diag. 11).
The contact points consist of an insulated, movable point
that connects to the coil primary lead, and a stationary
point that is grounded to the stator body. Spring tension
holds the points together making a complete path for the
primary circuit, and are opened by the action of the point
arm which rests on the ignition cam. The contact points
are a replaceable item (diag. 12).
The ignition cam is an oblong device which rotates with
the crankshaft, and opens the points for firing the ignition
system. It is important to check the ignition cam for
roughness, if rough replace the cam. When inserting the
ignition cam onto the crankshaft make sure that the side
stamped "TOP", or the side that has an arrow on it faces
the mechanic (diag. 13).
NOTE: SOME IGNITION CAMS ARE MACHINED
DIRECTLY ONTO THE CRANKSHAFT AND ARE NOT
REPLACEABLE.
The stator plate is an aluminum fixture which houses
the points, cam wiper, condenser, and has the laminations
riveted to it. The laminations are strips of iron riveted
together to form an iron core. Rust or debris in between
the laminations will hamper the performance of the ignition
system. If corrosion on the laminations is severe, the stator
plate should be replaced (diag. 14).
The flywheel key locates the flywheel to the crankshaft
in the proper position. If a flywheel key is sheared, or
partially sheared, the engine will not start or be difficult
to start (diag. 15).
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