Solenoid Conundrum

[Myrtles Man]

I'm in need of knowledgeable clarification on an electrical matter that is the subject of mild disagreement on another (non-Morris Minor) forum and I'm hoping that our in-house time-served electrical engineering contingent (geoberni and Sleeper come to mind) might be able to provide a definitive ruling. The matter concerns pre-engaged starter motors (unlike of course those fitted to Moggies) and this Youtube offering illustrates the problem and a suggested over-ride:-

https://www.youtube.com/watch?v=8n2eOwhG1gU

The contention of one side of the disagreement is that the introduction of an additional solenoid into the system as per Taryl's suggestion will invalidate the pre-engagement function of the car's existing solenoid by causing the starter motor to begin spinning as soon as the ignition key is turned, rather than operating the normal pre-engagement function (whereby the Bendix is thrust into the flywheel teeth prior to the starter motor spinning up), thereby effectively turning the system into a non pre-engaged one.

The other side contend that this cannot be so because the additional solenoid merely transfers battery voltage to the car's own solenoid (the equivalent of bridging the trigger terminal and the power terminal on that solenoid) so the pre-engagement function built into the solenoid will continue to operate normally. I shall be very interested to hear what our experts make of all this.

[oliver90owner]

Not really any conundrum at all.

The bendix is already spinning before engagement - mybe not full speed but certainly on the way to it. The solenoid, in that instance, is purely switching the motor to fully power it.

With a pre-engaged starter (note the pre-engaged part is an adjective) requires the solenoid to engage the starter dog before the motor is powered by the contacts. One could put twenty switches in series on the supply to the solenoid and it would only operate the motor solenoid on switching on the very last switch! Not a good idea putting in twenty switches in such a circuit but the idea is the same. A solenoid is only a switch.

[geoberni]

From what I could tolerate of that annoying faux Hill-billy video, it was a load of garbage.
If that starter has a duff Solenoid on top of it, then adding another one to the circuit does diddle squat.
How the pre-engaged works....

Stage 1 below, nothing operated, there are the 2 Red Connections as fiddled with by Bucky the Hill-Billy.

Stage 2 - When the Starter is operated by turning the key, the first step is the Solenoid Coil (3) starts to pull the arm across to engage the starter gear and the motor (Via S1 on the diagram) is given a little power to turn it relatively slowly. This lets the gear engage without smashing in too hard and fast.

Stage 3 - Once it's fully engaged there is the connection via S1 and S2, so the starter is fully powered and turning the engine

Pre-engaged Starter.JPG (61.73 KiB) Viewed 3915 times

Perhaps I missed somat, but from the looks of it, all our Lil'ol Country Boy did was wire it up like this, with an extra set of contacts now in the circuit...

Pre-engaged Starter 2.JPG (51.07 KiB) Viewed 3915 times

I think all it's actually gon an done is give a better supply to the original solenoid, he could probably 'ave gotten jus' as good results by cleaning up all the connections..

PS, all the above steps occur within about 1/2 second...

[philthehill]

If you fit a pre-engage starter motor the existing separately mounted (as per ex factory) solenoid should be isolated or bypassed.
The pre-engaged starter has a built in solenoid which firstly engages the starter Bendix with the flywheel ring gear and then secondly energises the starter motor windings to turn the Bendix when it has engaged with the ring gear. This happens in the blink of an eye and whilst there are two operations they will appear as one.
With a non pre-engaged starter motor the solenoid energises the starter motor windings which spins the starter motor and because of the way the Bendix is mounted on the starter motor shaft throws the Bendix towards the ring gear so engaging with the ring gear. The bevel on the ring gear teeth enables the non pre-engage Bendix to engage with the ring gear so overcoming the hit and miss function of the Bendix when engaging with the ring gear.
The pre-engage starter does not require the bevel on the ring gear teeth as the Bendix is directly engaged with the ring gear before it turns the ring gear.

[oliver90owner]

I think there is some error in considering that a pre-engaged motor has a bendix. It does not. The bendix was a device, invented by Hugo Bendix, to throw the starter pinion forward when the starter motor accelerated rapidly, from zero rpm (and be thrown out of engagement if the flywheel rotational speed exceeded that of the pinion.

In the case of the pre-engaged starter motor arrangement, the starter pinion is first mechanically engaged with the flywheel ring gear (by the action of an electrical solenoid on more modern engines) before the motor contacts are made.

The early pre-engaged starter motor pinions were manually engaged by the operator before the starter motor was energised. I have driven Ferguson, and early Fordson diesel, tractors with this arrangement.

One of the main advantages of the pre-engaged starter over the bendix type is that the pinion is not thrown from its flywheel engagement by the engine firing. Most diesel engines, particularly when very cold, require continuous cranking until the engine has sufficient power to overcome subsequent compression strokes. Spark ignition engines produced more than sufficient power to drive the engine past the following ignition point in the cycle.

The pre-engaged starter mostly took over from the bendix type, even on spark ignition engines - probably due to mass production standardisation and reduced wear of the pinion and flywheel gear.

[philthehill]

Whilst you may be correct about the title of the pinion/gear/sprocket that engages with the ring gear of the flywheel it is easier to call the pinion/gear/sprocket a Bendix for the purpose of the description and understanding of how the two systems work.
Sometimes it is better to not be so pedantic.

[Myrtles Man]

Thank you all for your thoughts and input.