1989/04/01 Caterpillar

Reference: Truck Engine News:

... December 17, 1984; Page 3; "Starters That Remain Engaged After Engine Is Running. "

... May 1987; Page 3; "Alternator/Generator Output Test On The Engine; " and Page 4; "Testing The Starter On The Engine."

... June 1988; Page 1; "Maintenance-Free Batteries Require Different Troubleshooting Procedures. "

... March 1989; Page 5; "Preventive Maintenance for Batteries. "

Reference: Special Instruction, Form SEHS7633, Battery Test Procedure.

Starter damage often results from attempting to crank with low battery (cranking) voltage on the electric starter. Engine ring gear damage may also result in this situation. There are three main reasons for starter failure:

1. Wearout during normal starter life (2000 to 5000 hours).

2a. Starter stays engaged with ring gear during startup.

2b. Starter attempts to reengage the ring gear after start-up.

3. Damage from low voltage on the starter motor.

1. Wearout refers to normal or expected starter life. The starter needs replacement because: the commutator brushes are too short, the nose housing bearing are worn (sloppy), or the solenoid contacts are no longer a good switch to connect the battery to the starter. The result is a starter that no longer cranks or might crank sluggishly. In this situation, the starter and starter solenoid shown no real visual signs of failure. The drive gear is NOT broken or blue from heat, the armature shaft is NOT blue, there are no "hot" spots sometimes easily visible on a painted housing.

2a. A starter, that fails as the result of staying in mesh with the engine ring gear during start-up, may show:

... blue, badly worn, or broken starter drive gear; or worn bearing.

... blue armature shaft in the nose housing.

... excessive wear in the armature shaft bearing of the nose housing.

... armature shaft that is locked up and cannot be rotated.

... "hot" spots in the paint on the brush end of the starter.

2b. A starter that is replaced because the drive attempted to reengage with a running engine ring gear shows one or more drive teeth "milled" or chewed up on the leading edge. This fault is usually caused by operator error or an intermittent faulty "start" signal to the starter from a start switch, start relay, or harness fault.

3. The results of low voltage on the starting MOTOR while cranking may be:

... sluggish cranking.

... no cranking, maybe only a "click. "

... starter can be heard to "chatter " or pulse the drive in and out of the ring gear at a rapid rate.

... solenoid gets hot and may even weld the contacts closed so that the starter tries to crank continuously, or may run (operate) without cranking the engine. See illustrations. The solenoid contacts show a burnt or "smoked" spot (and sometimes, melted) while the rest of the contact area shows previous starts were normal.

... one or more (but not all) starter drive teeth show case crushing of the hardened tooth surface.

... badly chipped, or broken engine ring gear teeth.

... bent armature shaft at drive end caused by engine "rock-back."

Illustration 1. Damage to solenoid contacts because of low batteries. See Illustration 2 for similar damage to contact disc.

Illustration 2. Damage to contact disc because of low batteries. See Illustration 1 for similar damage to solenoid contacts.

Illustration 3. Damaged contact disc because of low batteries.

Possible causes of the above results or faults are:

... low or no alternator output.

... loose fan belt(s) causing low or no alternator output.

... battery problems such as a shorted cell.

... poor/loose connections between the batteries and starting motor. This means anywhere in the positive or negative (disconnect switch) leads.

Illustration 4. Normal wear pattern on contact disc.