Starter motor earthing

I don't want to be a PITA pedant about this, but accuracy is important when describing things of a technical nature.

This is a Series 3 petrol 4cyl engine's starter motor:Attachment 191446 It functions by having current passed through its windings, causing the armature to spin. Inertia throws the pinion up the helical winding on the armature shaft and that engages with the ring gear on the flywheel. This will happen no matter how the current is applied. Direct battery connection is all that is needed. The only reason a relay is in the circuit is to protect the ignition switch from the very high current demands. The starter performs without it as long as the current to it is sufficient. You could replace the relay with a simple knife switch.

This is a Series 3 4 cyl Diesel engine starter motor:Attachment 191447 It also functions by having current passed through its windings. But, it has no helical winding on the armature shaft and relies on the action of the piston in the solenoid to throw the yoke connected to the pinion to engage with the ring gear, simultaneously with making the electrical contact to spin the motor. If you fit a remote "solenoid" to the windings of this motor it will spin until the battery goes flat but it will not engage the pinion with the ring gear. Ever.

Attachment 191448

I'll bet Paddocks call spring dampers "shock absorbers" as well. Common usage, but still wrong.

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Originally Posted by Tins

Just because a spare parts mob calls something by a name does not make it right. No wonder getting the correct part is so difficult.

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Funny that every supplier calls them a solenoid so do most people in the trade.

We can keep this discussion going for some time but the principles are very similar, solenoid or relay.

Colin

If you really want to be technical, a "solenoid" is a coil of wire, usually with an iron core, which is usually used to perform a mechanical function. This may be to close (or open) an electrical set of contacts (as in a relay), or to perform a mechanical function such as to engage gears or to do both, as in one of the more common types of starter "solenoids" seen today.

Series 1/2/2a 4cyl petrol Landrovers used a hand operated plunger switch on the firewall to switch power to the starter motor for starting, and used inertial engagement to engage the starter pinion with the flywheel ring gear. With the Series 3, this switch was replaced by a high current relay with a solenoid closing the contacts, with this solenoid or relay located in the same place as the previous switch. With either of these setups, a simple click on trying to start may mean either a very flat battery or, more likely, a starter that is having trouble turning due to being stuck in engagement with the flywheel or with worn bearings allowing the armature to be pulled hard against the stator poles.

Low battery or poor connections with either type of switch usually results in a "click-whirr" noise where the starter is getting enough voltage to spin, but not abruptly enough for the pinion to be thrown into engagement.

Note that to complicate trying to explain what is likely to be the problem without actually looking at the setup, it is entirely possible, perhaps even likely, that new starters, incorporating a solenoid that engages the pinion as well as switching current are being sold as replacements for S3 starters