Ford Starters: 4,4MOD, 4.5 Positive Engagement By Larry Wilhelm Ford starters have a history of chatter- ing while being tested in a free spin mode. Free spin is when the battery power is applied to the starter and it is not installed to the engine. This test allows the starter to spin without any torque driving load. These starters have a differ- ent design than most other starter motors. The starter is called a series-parallel compound design. In addition to most other starters, Ford added a shunt coil with a different engagement mechanism. The shunt coil is made of about 80 turns of small wire. This is placed in the same position as one field coil. The field coil cannot pull in the pole of the engagement mechanism alone. More magnetism is required. This added shunt coil helps to provide the required magnetism. Battery voltage is applied to the shunt coil and the one field coil to engage the starter drive. As soon as the two coils (working together) pull the pole shoe into the starter case hole (starter drive engage- ment position), a switch opens, changing the current flow through the field coil. The field coil current now flows through a second field coil and through the arma- ture. Initially, the one field coil is across the battery, providing excessive current and magnetic forces. The current is much lower (lowering magnetic forces) when it is in a running position. When the starter is in the engagement position, less magnetic forces are required to keep it in the engagement position. Current through the field coil is enough to keep the starter engaged when cranking the engine. This current has an initial inrush which is even higher than the cranking current. After the starter is spinning, the current will be relative to the load on the starter. In a free spin con- dition, the current becomes low enough that it may not hold the starter pole shoe in the engagement position. The engage- ment will drop out, pull in, and drop out in a repetitious cycle, causing chatter. When using a car battery or many test benches, this chatter may occur. The starter may be OK, but the field is not providing sufficient magnetism to hold in the pole shoe for a free run condition. The test would still be valid if the pole shoe was held in during the free run test. This is not a recommended procedure. Bodily damage could occur while attempting to hold the arm in. If chattering occurs in your testing, you may assume the engagement func- tion is OK. There is enough magnetism from the two coils to pull in the arm. This is the most magnetic force required. If the starter chatters while testing for amps and free run, one can still test with the following procedure. Remove the pole shoe (thin metal) cover. Insert some insulating material between the electrical contacts, under this cover, so that current cannot pass through the con- tacts. Be careful not to bend the contacts or change their alignment and spacing adjustments. Keep hands free from all starter parts. Test the starter for free spin and amps by applying the battery voltage to the case and the battery terminal. The starter will spin but it will not remain, or chatter, in the engagement position dur- ing this test. Coil magnetic forces are calculated by the amount of turns of the coil times the current flowing through the coil. The field coil has very few turns. With very few turns, the current must be very high for magnetic forces. When the starter is cranking the engine, the amps, times turns, is about 1,000. When the field coil is connected across the battery, the amps, times turns (pull in force), is about 7,000. When the starter is free running, the amps, times turns, is about 500, making it difficult to hold the pole shoe in the engagement position. Some new batteryless testers provide more power to the starter to overcome this chatter. Others provide a signal when the line voltage is too low to provide a proper test. When the low voltage is alarmed, the starter is bad or the line voltage is too low to test. Check with an electrician to make sure there is proper wiring directly to the tester. Starter testers, without batteries, must have sufficient line voltage and proper wiring. A rebuilt or new Ford starter that chatters in free run will (in most cases) function properly when mounted to the engine. Larry Wilhelm, formerly of ACE Electric, Columbus, KS.