The strength of the BMW M4 Coupé is evident in every detail.
I received a panic call from a neighbour last week. His car, “which had been behaving perfectly”, would not start. The engine refused to turn via the starter and the neighbour feared that the engine might have seized.
I thought seizure was most unlikely. It sounded more like a duff battery, corroded terminals, or a starter motor pinion staying in mesh with the flywheel teeth due to wear on the pinion, the flywheel or both.
I decided to try the easiest test before getting my hands dirty.
This involved no more than selecting third gear and, with ignition off, rocking the car to and fro. It was one of my lucky days, because the pinion immediately freed itself and the engine could be turned over and started.
Many times in the past, when confronted with such a problem, another solution was to use a spanner to turn the protruding square end on the starter. However, most starters no longer have such a protrusion and rocking the car usually does the trick.
When a starter jams, the symptom, apart from the engine failing to turn, are that the lights will dim. But if the starter motor will not turn, the headlights do not dim and the solenoid operates, then the starter itself is faulty.
On later cars with no protrusion, you can slacken off the starter’s securing bolts and pull the armature back. Whichever way you choose, it is wise to remove the starter as soon as possible to examine the flywheel and pinion teeth.
As I mentioned earlier, poor/dirty battery connections and even loose earth strap connections to engine and body can produce such symptoms.
WHEN TO SUSPECT THE BATTERY
If there is no more than a click when the starter is operated and especially if there are white deposits around the terminals, suspect the battery.
To test, disconnect the coil feed terminal and select neutral, then try cranking the engine. Under normal temperature conditions it should spin freely and battery voltage should be about 10 volts. If it is sluggish, it is only fair to say there are many possible culprits, apart from the battery, such as a faulty starter, cables that are past their best, resulting in loss of voltage, connections or solenoids.
I haven’t seen one for a while, but some cars used to have a button under a rubber cover between the main terminals. This was a handy thing to start the engine without having to get into the car. It was also a godsend that enabled starting when a solenoid winding failed.
Note that you should always disconnect the battery before removing a starter motor from a vehicle. Brushes wear and renewal is called for if they are found to be less than 8mm in length.
Poor meshing between the flywheel and drive pinion and sticking may be caused by accumulated dirt. Test inertia drive spring strength by trying to turn it by hand. It should not be possible to do so.
Brush on petrol to clean the drives, but resist the urge to go heavy on oiling. The shaft may be very lightly oiled. The spiral grooves must be clean, but they must also run dry. Oil or grease will encourage the build-up of dirt. -Star Motoring