Starter motor, need explanation.

[Ben Hutchings]

Hi, lastnight I started the car and the starter stayed on after it fired up, I cut power and the starter continued to spin. I had to pull the battery leads to stop it. When I 'touched' the leads to the battery again it cranked the engine over (with ignition off)

This morning I took the starter out and the spring on the end of the pinion is broken, so I guess thats the problem.... or is it?

Presumably it's only the solenoid that powers the starter while in the ignition is in the 'start' position, so the spring breaking should have nothing to do with the starter constantly spinning right? Or is there some sort of electrical latch setup in the starter that once it's engaged it keeps itsself powered until the engine kicks it back down the shaft?

This is semi-urgent, as I have to drive this thing to Cornwall on Tuesday so basically have 1.5 days to fix it in (if I need to order stuff)

Thanks!

[gravelrash]

Do you have seperate solenoid or pre engaged starter? Have known it with bikes that the solenoid itself corrode inside and the plunger sticks in its bore. Not something that is repaired easily.
If you have power accross the solenoid all the time then I would say the soleniod is at fault.

Ade

[Ben Hutchings]

I have sepreate push button sort solenoid.. damn, I thought that was faulty, but was hoping not as it's only 6 months old and has probably been used about... 20 times.

Ok thanks a lot.

[JohnD]

If you have a spring on the end of the starter pinion shaft, then it's not a pre-engaged starter.   But I think that broken spring is a symptom, not the cause.

The standard starter has an 'inertia' or Bendix drive, so that when the electric power spins the motor, the pinion is thrust back along the shaft, against the spring, into mesh with the starter ring on the flywheel.  This pinion movement is entirely passive.
The remote electrical relay that switches the very high current from battery to starter is sometimes called the 'solenoid'.  This should not be confused with the solenoid in a pre-engaged starter that actively thrusts the pinion into mesh with the starter ring, before the starter motor begins to turn. Hence "Pre-engaged"!

Both are 'solenoids', that use an electromagnetic field on a permanent magnet to cause linear motion, but the first is tiny and only turns a switch, the second moves a large piece of metal.

I suspect that your starter relay switch has jammed.   The starter goes on turning as the engine runs, keeping the pinion in mesh and this has broken the Bendix spring.   You need a new starter switch - the one on the bulkhead, NOT the one you put your key into! - and a new spring in your Bendix drive.     A special tool is needed to compress the Bendix device and replace the spring, so a re-conditioned starter is probably the best way to go.
  The starter relay switch cannot be repaired, but take the old one apart when you remove it, to see how it works (worked!) and what has damaged it.   Corrosion may have jammed the internal solenoid, and/or the contacts may have welded together - it normally handles 30+Amps!

If you have to drive before you have the parts, start by briefly connecting the starter cable, then disconnecting it.   This may work if the pinion still functions as described above, and once the starter is disconnected, the pinion should retract and no further damage will happen.   But keep the end of the starter cable isolated. It is 12V live, can carry many amps and could easily start a fire if it contacts another part of the engine or bodywork.

Good luck,
John

[Ben Hutchings]

Thanks very much John, great explanation!
Tim is picking me up both solenoid and starter today.

[James]

Heh - I have a spare mk1 starter sitting in the back of my car!