Starter shorting/cooking wires

[leeandoona]

So. My minor which has sat idle for many many many months wouldn’t start or even turn. It’s a 58 and has a pull starter. When pulling the starter knob the dash lights dim. I checked the power to the starter motor and sure enough there was no power reaching it. I bridged the connection on the switch but this did nothing and did a volt meter test and no power was jumping from one side to the other unless bridged. I tested the starter independently and discovered it too was not working so removed it, bench tested and sure enough it was dead.
During all this I noted the wires were getting very hot when attempting to start/power the starter.
So I checked and cleaned all the earths, including the gearbox earth strap. Bought a new starter which I bench tested and confirmed was operating. Fitted the starter, pulled the starter knob and the starter span once and then after an audiable bang, it stopped working and returned to hot wires and dimming cabin lihjts.
Checked fuses, checked earths again. All lights operate as expected so appears to be electrically okay on that side of things. Removed new starter to discover it too is now dead. So it’s cooking starter motors. I’m assuming this is a short?
I’ve bought a new starter switch/solenoid (I know it’s not really a solenoid).
Anyone had this happen? I don’t really want to fit another starter and Jill that too!

[oliver90owner]

First thing - can you confirm that the engine actually turns?

Further response after that.

[StillGotMy1stCar]

Is the engine seized overloading the stalled starter motor. Can you turn the engine with the starting handle, fan or rocking in gear.

Regards John

[leeandoona]

Engine turns freely. Yes. Not seized and I e turned it over using the starting handle.

[oliver90owner]

Was the replacement starter motor a secondhand purchase or bought from a reputable source of refurbished starter motors.?

If the latter, I would think they should replace the unit. I cannot understand how the starter should fail so quickly. The loud bang would indicate something is shorting inside the starter motor. I’m assuming, here, that you did not engage the power for too long.

[leeandoona]

Brand new from reputable minor specialist. No, it was literally one pull on the starter and a brief spin over of the engine, then bang and failure.

Wires from starter and to battery very hot. Can’t see any obvious signs of bad earth, all earth points nice and
Clean and when checked for continuity they show appear normal.

I’m assuming there is a short somewhere?

[oliver90owner]

Yes, there is definitely a short circuit somewhere. The starter motor windings should show a very low resistance, so not easily checked for true answer with a cheap multimeter. It would draw upwards of 200A at zero speed, so resistance of around 0.05 Ohms, and 60-70A when up to speed (impedance, rather than resistance while running).

Talk to your supplier is my advice.

As a further check is there a short circuit when operating the starter switch while the starter motor is disconnected? That should then be an open circuit (so no light dimming, etc).

[geoberni]

Something is certainly not right, that's for certain.

Was the bang from the starter?
Did you go inside to pull the knob, or push the central button on the switch under the bonnet?

As Oliver asked, with the cable disconnected from the Starter Motor, and the end insulated from touching anything , what if anything happens when you operate the Start Switch?
There should be nothing at all happening.

I can't see a way for 'the car' to make the Starter go 'Bang'.....especially since you say the engine will rotate on the handle...
It's pointing to a faulty Starter, but what's the odds of a replacement having the same fault as the original... Not really likely.

I think you need someone with basic electrical knowledge/competence to come and look at it.
Remote diagnosis is not really practical; there's very likely something going on that you're not thinking to tell us about, you may not even be aware of it (whatever it is).
Those supply cables getting hot can only indicate a massive 'dead short'; they should take 200 amps or so for several seconds before even warming up. If you keep playing with it you're risking damage to the battery.

Can you post photos of the installation, showing the Starter Sw and the Starter, including all connections to them.??

[Paladin1962]

I'm leaning towards a failed bendix gear. It's probably jammed against the transmission case.

[oliver90owner]

I'm leaning towards a failed bendix gear. It's probably jammed against the transmission case.

Do tell us how you have come to that “leaning”. OP says starter momentarily spun the engine, so the bendix must have been meshing with the flywheel?

I’ve never caused a starter motor failure when the bendix has jammed in the flywheel and unable to turn over the engine. To hit anything within the bell housing, the starter motor would have to be seriously bent?

I’ve never had a starter motor go ‘bang’ and fail, either.

[svenedin]

I have had a starter motor seriously overheat and start to smoke when the solenoid jammed on. That was very alarming and I could not stop the starter motor until I disconnected the battery! I immediately fitted a quick disconnect after that.

I don't understand why the new starter motor went bang and failed. Was the bang actually the starter motor or something else? The wiring is so simple that there's very little to go wrong. Starter pull cable, starter switch, heavy cable from battery to starter switch, heavy cable from starter switch to starter motor and earth provided by gearbox earth strap. Can you test each part systematically? Is a cable damaged internally causing high resistance? Is the insulation on a cable damaged causing a dead short? Is the starter switch faulty? Is the starter switch shorting to its metal body? You say you cleaned the earth strap. Did you test its resistance?

Stephen

[oliver90owner]

High Resistance: This always reduces the current as the resistance rises. Normally the point of higher resistance overheats - a local point of overheating - often a battery terminal (which could melt!) or another joint which will soon smoke because there is little chance of sinking that heat away from the joint.

Are we not talking, here, of low resistance? The problem with a starter motor is that of no impedance whenever the starter motor fails to start turning.

To seriously over-heat a starter motor requires overly long operation if it is simply a jammed solenoid. Extended cranking, to start an engine is warned against.

This post is about near zero resistance - an almost dead short - apparently after the starter motor has failed. We rely on accurate details from a remote user. Not always sufficient, but that is all we have to work with.

[geoberni]

I'm pretty sure that if anyone with an understanding of basic vehicle electrics had a few minutes looking at it, the answer would be found.
All our speculation is just that, because we're not there to see it.....
I asked for some detailed photos on Monday in the vain hope of noticing something not right.....

[svenedin]

High Resistance: This always reduces the current as the resistance rises. Normally the point of higher resistance overheats - a local point of overheating - often a battery terminal (which could melt!) or another joint which will soon smoke because there is little chance of sinking that heat away from the joint.

Are we not talking, here, of low resistance? The problem with a starter motor is that of no impedance whenever the starter motor fails to start turning.

To seriously over-heat a starter motor requires overly long operation if it is simply a jammed solenoid. Extended cranking, to start an engine is warned against.

This post is about near zero resistance - an almost dead short - apparently after the starter motor has failed. We rely on accurate details from a remote user. Not always sufficient, but that is all we have to work with.

OK agreed. A focal point of high resistance such as damage to a cable internally would cause local heating at that point due to high resistance. A short would cause low resistance and excessive current to flow causing the whole cable to heat up. A hypothesis that incorporates both situations is, the cable was damaged internally causing high resistance and local heating. The insulation burned leading then to a dead short.

Nonetheless I do not understand why a short blows up a starter motor. Surely if there's a short in the circuit before the starter motor then the starter motor just fails to operate?

Although I don't like "parts darts" (replacing parts without knowing that they are definitely faulty) for the sake of 2x cables I would replace the battery to starter switch and switch to starter motor cables if in any doubt about their integrity especially if there is any sign of the insulation failing. I would also be testing the starter switch.

I suppose it is possible that the new starter was just faulty. The new ones are Far East manufacture I believe and not of the quality of the original Lucas products (mine was the original until a couple of years ago, they are dated on the case and it lasted 55 years).

I would suggest that after testing everything that the OP gets a refund on his new starter motor (if it was faulty in manufacture) and then buys a refurbished genuine Lucas M35G/M35J suitable for a Morris Minor.

One last thought. Is the new starter motor actually faulty or did the OP use the same cables (which may be damaged) to test it?

Stephen

[simmitc]

If the connection to the starter motor was made incorrectly, perhaps undoing the terminal securing nut and connecting the cable so that it was touching or close to the body, then that could create a short, and with internal wiring disturbed, quite possibly a bang.

A picture would definitely help. Leeandoona - could you please post a photo of the connection to the starter, but pull the insulating boot cover (if fitted?) away so that we can see the terminal.

[svenedin]

Good point Simon. I had not considered this.

The live terminal of the starter motor is insulated from the body of the starter motor. If it was not insulated there would be a dead short.....

The cable from starter switch (or solenoid on key-start cars) is clamped between 2x nuts on the terminal post. Underneath the nut nearest the starter there should be an insulating washer and an insulating bush.

Pictures show starter as connected in my car (ignore the plastic connector which has nothing to do with the starter) and a rusty old starter I have in the garage.


As connected in car:

IMG_2308.jpeg (529.11 KiB) Viewed 84 times

Old starter motor. The cable goes on top of the nut and is clamped by a second nut (not shown)

IMG_2309.jpeg (2.82 MiB) Viewed 81 times

[jaekl]

I don't think the OP mentioned what the started did when bench tested. All he said was both didn't work. I don't recall him stating that there were any symptoms of shorting within the starter. Any fault in the circuit before of after the starter would not cause excessive heating of the cables. Resistance in the cable could produce heat but there would be no voltage left to run the starter but is the field circuit good enough to support the current to allow the cable to draw current to heat itself? If this is the failure in both starters, the circuit would no longer heat up, but I think it was stated that the condition continues in the car as opposed to heats up and then nothing. To me it points to a dead short through the starter or the supply is shorted to the body which would not damage the starter. What is the resistance through the starter?