If Lights Dim

If the lights dim considerably as the starter switch is closed and the starter operates slowly or not at all, the battery may be run down, or there may be some mechanical condition in the engine or starter motor that is throwing a heavy burden on the starter motor. This imposes a high discharge rate on the battery which causes noticeable dimming of the lights.

Check the battery state of charge. If it is charged, the trouble probably lies in either the engine or starter motor itself. In the engine, tight bearings or pistons or heavy oil place an added burden on the starter motor. Low temperatures also hamper starter motor performance since it thickens engine oil and makes the engine considerably harder to crank and start. Also, a battery is less efficient at low temperatures.

In the starter motor, a bent armature, loose pole shoe screws or worn bearings, any of which may allow the armature to drag, will reduce cranking performance and increase current draw.

In addition, more serious internal damage is sometimes found. Thrown armature windings or commutator bars, which sometimes occur on overrunning clutch drive starter motors, are usually caused by excessive overrunning after starter. This is the result of such conditions as the driver keeping the starter switch closed too long after the engine has started, or the driver opening the throttle too wide when starting vehicle. Any of these subject the overrunning clutch to extra strain so it tends to seize, spinning the armature at high speed with resulting armature damage.

Another cause may be engine backfire during cranking which may result, among other things, from ignition timing being too far advanced.

To avoid such failures, the driver should pause a few seconds after a false start to make sure the engine has come completely to rest before another start is attempted. In addition, the ignition timing should be checked if engine backfiring has caused the trouble.