20 replies to this topic

[Davris1373]

Hi there, I've got a 1991 Rover Mini Cooper SE and the starter motor has failed. The solenoid is still good and tested, but the motor's 12V line is shorting to ground.

I've removed the two bolts that hold it in place but it won't come out. I've tried using a spanner between the motor and the engine block to lever it out: it didn't budge. I've even tried putting my jack under it: it's held on so well that it supported the weight of the car without budging...

Any suggestions are greatly appreciated

[slidehammer]

Firstly, I wouldn't put a jack on it. It is probably held in just by corrosion of the aluminium casing. Spray some penetrant around the join between the starter and the flywheel casing and let it soak in then tap it with a block of wood to rock it out. You could also try twisting it to break the hold.

[alpder]

The starter motor's + terminal may appear to short to ground, but the internal resistance of a starter motor is surely next to nothing (maybe a few hundredths of an ohm). That's how they can pull hundreds of amps from a mere 12V. So measuring it and seeing approx "0" with a typical multimeter on 200-ohm range would be the value I expect to see anyway and isn't indicative of a fault.

[stuart bowes]

shock it with taps from a rubber mallet if leverage isn't working, it'll break free eventually 

 

what was the original cause of the issue and what other diagnostics have you done, it could be something else at fault as mentioned above (or at least the test you did isn't conclusive by itself)

[alpder]

When you get it free, and bench-test it... please do be sure to clamp it down. Or better, test it on the floor, not on a waist-height bench. Despite being heavy they start with a massive kick and can easily throw themselves off the bench. No fun having one land on your foot.

[Davris1373]

The original problem was when I got in the car and turned the key to position 2 everything came on as usual and my volt meter displayed 12.8V. I turned the key to position 3 and heard the solenoid engage but then all the electrics died.
I unplugged everything other than the starter relay, solenoid, and motor and the same thing happened. I've checked the relay and it's fine, checked the solenoid and it still works so the only think left in that circuit is the starter motor.

I soaked it in wd40 over night and still won't budge, I'll try tapping it with a rubber mallet tonight and see if I can twist it

[alpder]

There are some simple electrical tests worth doing, which can rule out some other common causes. Requires three hands tho'...

 

(0) Check the battery is well charged Check car is in neutral. Keep fingers clear of mince-y bits in the engine bay...

 

(1) Measure battery voltage directly on the battery terminals. Will be about 12V. Continue to measure and turn key to crank. If no cranking happens and voltage drops several volts below 12V then battery is probably sick. Or starter is jammed... in which case considerable heating/smoke will also be observed, and battery should be disconnected until resolved.

 

(2) Measure voltage across the solenoid output terminals (i.e. between the term that goes direct to the motor windings and the term that's connected direct to the bat+, with the probes on the male threads themselves, not on the cable eyes or the nuts). Should be 12V. Continue to measure and turn key for cranking. Should change to 0V.

 

(3) Measure voltage from battery neg/ground post (the post itself, not the clamp) and the engine block. You'll need a piece of wire to extend one probe. Should be 0V. Turn key to crank: should still be near-as 0V. If it's not, then you've an earth-lead fault.

 

(4) Measure voltage between battery + post (the post itself) and the battery terminal of the solenoid. Should be 0V. Turn key to crank and measure again. Should still be near-as 0V. If it's not, then there's a fault in the main battery cable.

 

[Davris1373]

I'll test these tonight and let you know the results

[nicklouse]

Have you drop tested the battery? It might show 12.8v but might be not holding any ampage to turn the motor. 
 

what you describe is typical dead battery.

[alpder]

 

Bear in mind in several tests you're looking for 0V as the indication that things are good. But lack of contact between probe and metal (caused by 30+ years of corrosion) can obviously also give a falsely reassuring 0V reading. So be sure to dig the pointy tips of the probes into the metal when taking readings.

[Quinlan minor]

The original problem was when I got in the car and turned the key to position 2 everything came on as usual and my volt meter displayed 12.8V. I turned the key to position 3 and heard the solenoid engage but then all the electrics died.
I unplugged everything other than the starter relay, solenoid, and motor and the same thing happened. I've checked the relay and it's fine, checked the solenoid and it still works so the only think left in that circuit is the starter motor.

 

If the battery is failing ( a cold winter will often kill a battery), or the battery earth path is bad, that would give exactly the same symptoms.

I'd advise leaving the starter motor alone until you have checked with a known good battery.

 

[Ethel]

A stalled motor has very little resistance, so the pinion could be stuck on the ring gear. If the solenoid is good you should hear the clunk as the gears engage & release.

 

Normally, the voltage would drop so the solenoid can't keep itself engaged - that clattering you'd hear with a flat battery. 

 

If it's seized , as Slidehammer suggested, there's a risk you could crack the transfer case. Tap it back & forth and try turning it around the motor's axis. Pushing the car in gear should show if the starter gear is stuck in engagement.

[Cooperman]

When you get it free, and bench-test it... please do be sure to clamp it down. Or better, test it on the floor, not on a waist-height bench. Despite being heavy they start with a massive kick and can easily throw themselves off the bench. No fun having one land on your foot.

Been there, done that  . A long time ago though!

[stuart bowes]

if you do get it off, test it from a car with a good battery, that's what I did on mine after the rebuild just to check it 

 

pair of jump leads and a fat screwdriver to bridge the solenoid connection, on the floor in front of donor car, and yes hold it steady 

[Davris1373]

There are some simple electrical tests worth doing, which can rule out some other common causes. Requires three hands tho'...

(0) Check the battery is well charged Check car is in neutral. Keep fingers clear of mince-y bits in the engine bay...

(1) Measure battery voltage directly on the battery terminals. Will be about 12V. Continue to measure and turn key to crank. If no cranking happens and voltage drops several volts below 12V then battery is probably sick. Or starter is jammed... in which case considerable heating/smoke will also be observed, and battery should be disconnected until resolved.

(2) Measure voltage across the solenoid output terminals (i.e. between the term that goes direct to the motor windings and the term that's connected direct to the bat+, with the probes on the male threads themselves, not on the cable eyes or the nuts). Should be 12V. Continue to measure and turn key for cranking. Should change to 0V.

(3) Measure voltage from battery neg/ground post (the post itself, not the clamp) and the engine block. You'll need a piece of wire to extend one probe. Should be 0V. Turn key to crank: should still be near-as 0V. If it's not, then you've an earth-lead fault.

(4) Measure voltage between battery + post (the post itself) and the battery terminal of the solenoid. Should be 0V. Turn key to crank and measure again. Should still be near-as 0V. If it's not, then there's a fault in the main battery cable.

Thank you for your responses everyone, they've been really helpful so far!

0) I took the battery out and fully charged it though a mains adapter.

1) 13 V over the battery and no change during cranking.

2) 13 V before cranking, 0 V during cranking, returns to 13 V when key is turned back.

3) 13 V measured after cranking between engine and battery -ve terminal, 0 V before cranking.
0.2 ohm before cranking and 130k+ ohm after which slowly drops to 0.2 ohm.

0.2 ohm between the engine and the front subframe before and after cranking.

4) 0 V between the battery +ve and the solenoid, no change with cranking.


I haven't tried with a different battery yet, I'm charging an old one up.

Test 3 tells me it's an earthing issue, any ideas where to go from here?