MerCruiser 13, Service Manual

Page: 176 / 348

IGNITION SYSTEM - 4B - 5 90-816462 2-695
Contact Points
1. Examine contact points for dirt, wear, pitting and
misalignment. Dirty points should be cleaned.
Normal point condition is an overall grey color on
contact surface.
2. Check for point resistance. A voltage drop of less
than .125 volts across points should exist. Make
this check with a sensitive volt meter or point re-
sistance meter.
ABNORMAL POINT WEAR
1. Points, which have been operated for period of
time, have a rough surface, but this may not mean
that points are worn out.
2. If points burn or pit, however, they soon become
unsatisfactory for further operation. Not only must
they be replaced, but ignition system and engine
must be checked to determine cause and elimina-
tion of trouble. Unless condition is corrected, new
points will provide no better service than old
points.
CLEANING POINTS
1. Dirty contact points should be dressed with a few
strokes of a clean, fine -cut contact file. File
should not be used on other metals and should
not be allowed to become greasy or dirty.
IMPORTANT: Never use emery cloth to clean con-
tact points.
2. Contact surfaces, after considerable use, may
not appear bright and smooth, but this is not nec-
essarily an indication that they are not functioning
satisfactorily. Do not attempt to remove all rough-
ness nor dress point satisfactorily. Do not attempt
to remove all roughness nor dress point surfaces
down smooth. Merely remove scale or dirt.
3. Badly burned or pitted contact points should be
replaced and cause of trouble determined and
corrected.
BURNED POINTS
1. Contact point burning results from high voltage,
presence of oil or other foreign material, defective
condenser and improper point adjustment.
2. High voltage causes excessively high current
flow thru contact points which burns them rapidly.
High voltage can result from improperly adjusted
or inoperative voltage regulator.
3. Oil or crankcase vapors, which work up into dis-
tributor and deposit on point surfaces, cause
them to burn rapidly.
4. If contact point opening is too small (cam angle
too large), points will be closed too long. Average
current flow thru points will be too high, so points
will burn rapidly and arcing will occur between
points.
5. High series resistance in condenser circuit will
prevent normal condenser action, so contact
points will burn rapidly. This resistance may be
caused by a loose condenser mounting or lead
connection, or by poor connections inside con-
denser.
PITTED POINTS
1. Contact point pitting results from an out-of-bal-
ance condition in ignition system which causes
transfer of material from one point to other so that
a tip builds up on one point while a pit forms in oth-
er.
b
a
+
+
–
–
Material Transfer
a - Negative to Positive
b - Positive to Negative
2. If points are pitted, replace condenser (and
points).