Trouble-Shooting Instructions - Fiat 411 R Service Manual

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The battery being normally charged, and the starting motor operated, causes the iollowgi-,9 headfigm
behaviour:
1) No light: traced to poor connections between battery and motor, or corroded battery terminals,
2) Considerable dimming as engine is started, and the latter runs slowly or stops:
a) excess of oil crankcase density;
b) armature spindle bent, bushes and support worn, and polar shoe screws toose;
c} commutator damaged, series field coil or armature coils grounded or short-clrcuited.
3) Bright headlights, and starting motor cranking slowly or stopping:
a) ioose terminals of the motor solenoid contacts oxidized or insulated by foreign matter intrusion,
or damage of the excitation circuit and commutators circuits; . ,
b) poor or iauity brush contact on commutator.
Troub§e~shooting instructions.
item 1) of the preceding chapter, increases the ohmic resistance laetween batteries and motor and may
be measured by a voltmeter, when motor is running. '
The voltage drop measurements to be taken are as follows: between tractor body and battery negative
pole; between tractor body and the electric motor frame; between battery positive poie and the solenoid
terminal, where the battery feeding cable ends.
Each measurement should not give more than 0,1 V, when the starting motor is running.
However, if the voltage drop is excessive, disconnect the cables, clean the battery terminals and smear
them with vaseline, to prevent corrosion.
items 2} and 3) oi the preceding chapter, call for a commutator check for efficiency and the removal of
the starting motor, to perform its test with no load and when stopped (torque test).
The following cases may occor when such tests are being performed.
l - Torque current and speed up to specifications,
it - Low speed and torques with no»load; high current drain: trouble to be traced to armature winding
partly short circuited, or grounded; or to rnechanicai defects, such as worn-out bushes, armature shaft
bent. loose poiar shoe screws.
A simpie inspection may indicate that some armature turns are grounded, as the corresponding corn-
mutator blades would be deteriorated by heavy current passage that wouid take place through the
brushes.
Ill-Motor does not start and high current drain: might be caused by the armature or the iieid coil completely
grounded.
IV-Motor does not start and no current drain or less than 24 A: no current drain requires checking the
solenoid contacts on the commutator, and of the brush spring performance.
Very low current drain signifies that the tieid series winding is interrupted.
The solenoid winding interruption may be checked with a test lamp.
V' LOW Speed. with no load low current and torque, the fault may be traced to the internal resistance or
The m0f<>F, or to commutator expanded bars due to centrifugal force.
The first trouble is reacliiy detected when the motor is dismantled, the second one may be caused by
the tree~wheei too hard to turn or by field coil connections unsoidere-d from the commutator bars.
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