Starter Motor not Engaging - Advice Please

[John Cornforth]

Hi JohnP

The way I suggest for measuring low resistances (when you have limited resources) is this: Take a 6V car battery and a spare headlamp bulb. Wire these in series, and then wire the combination in series with the low resistance item you want to test. The bulb will light up to normal brilliance, and limit the current flow to something close to its rating, e.g a 36 watt bulb will draw 6 Amps at 6 Volts. Now, take your digital DC voltmeter and set it to its most sensitive range (or let it auto-range). Place its probes either side of the junction, stud, rivet, piece of wire, switch etc that you are trying to measure and note the voltage drop. With 100 milliohms and 6 Amps test current you will see 600 mV, with 10 milliohms you will see 60 mV etc. If the resistance under test is too high you will begin to lose accuracy as the current won't be the full amount, but for anything up to 100 milliohms you won't be far off.

A 12V battery will work just as well, and an old 55 Watt foglamp or somesuch will give you a test current of about 5 Amps.

If you have a DC ammeter you can always measure rather than estimate the test current, but this isn't supposed to be a lab experiment, just a way of finding a dodgy contact !

[Dave Mann]

Ah this is jogging my memory of a reluctant starter many years ago, this was a 3 speed starter and the internal soldered connection below the main terminal was defective.

[Bob Kneale]

John,

I've only got a low cost digital multi-meter but could I get any meaningful results using this.

John.

Hi John

One of the many problems Austin Seven owners have is trying to measure electrical values with DIGITAL instruments. They are too responsive to rapidly changing electrical values, Voltage or current or resistance to give a meaningful reading, and you would probably be more successful using the old fashioned ANALOGUE meter, which gives a much steadier reading under conditions experienced in a motor vehicle environment. I've been following this with interest having suffered this (and lived with it) and only cracked it by making sure every connection was extremely low resistance. Analogue multimeters are less easy to find than they used to be, but even a cheap one will be more help with wha t you are doing and by the end of the exercise/ordeal,you will have a very thorough working knowledge ad ability of matters involving ohm's law,voltage current and resistance.Don't be afraid to ask for advice from gurus like John Cornforth, for he talks a lot of practical sense.

Good luck and don't give up - yet!!!!!
Bob

[John P]

Well, spent another few hours on this today but not sure it's made much difference.

Earlier today I spoke to a possible repairer who suggested I make sure there was no lateral movement of the armature in it's bearings which might allow it to contact the field coils so once again I stripped it all down and this time also took out the ball race at the pinion end but it all looked OK.

Whilst it was in pieces I again checked for continuity of the field coils and that there was no short to earth and it looks fine.

The armature windings are actually strips of solid copper which I believe is called a bar armature.   The construction is so solid it seems extremely unlikely there could be a break in these and, in any case it all seems to check out OK.

I then cleaned up the terminals which connect to the brushes and also cleaned the faces between the central motor casing and the ends just in case this was creating high resistance in the earth side.

When I reassembled the brushes I did notice that although the earth brush seemed to mate well with the commutator the live brush was only touching over a relatively small part of it's surface so I used some abrasive paper between the brush and commutator to bed this in which I hoped would be the answer.

Finally I again thoroughly cleaned the Bendix assembly and re-assembled everything.

Laying on the floor and connected to the battery with jump leads it spins up well but doesn't have the violent acceleration others have mentioned.

I think all I can now do it to try to bend the pinion clip so that it barely holds the pinion and then mount it back on the engine to see if it will engage and if it has the power to turn the engine over.

If that fails I'll have to accept defeat and take it to a specialist.

[John P]

If anybody is still sticking with this thread then IT'S WORKING!!

Not sure what was really wrong but having eased off the retaining clip and re-fitted the starter this morning it now engages and turns the engine over nicely.

Got a few other things to sort before I can actually run the engine but at least this bit seems OK.

Thanks to everyone for their suggestions and for encouraging me not to give up.

John.

[Ivor Hawkins]

Thanks for reporting back John, that is brilliant news and gives me some hope as I have had exactly the same problem, as you know.

As well as very carefully skimming the commutator, checking continuity like yourself, I even baked the armature for two hours at 100 degrees, but haven’t had a chance to test the starter yet because I am waiting for my heavy duty jump leads arrive.

I’ll ease off the retaining clip a tad and keep my fingers crossed and report back.

Well done!

[Colin Wilks]

Hi John

For no particular reason I have found myself urging you on from afar on this one, so I am absolutely delighted that you have got it working. The fact that it's now working and you don't quite know why does I think neatly encapsulate the joy of working on these cars!

Best wishes, you are now officially an electrical genius!

Colin

[Ivor Hawkins]

Well, I promised to report back, the new jump leads arrived and I loosen off the retaining clip and the starter dog spins up the Bendix nicely when bench testing.

However, on the car it just clunks into the flywheel and does nothing, so I’m hoping it’s either a duff battery or properly fixed leads will improve the situation.

I’m not going to mess around any longer, I’ll crack on with the build, which includes a complete re-wire and we’ll see what happens...I’ve always got the handle!

[jpsmit]

could it be an alignment issue? Or the teeth not engaging properly?

[Ivor Hawkins]

Sorry if you are all a bit bored with this one, but I’ve run some more tests with a voltmeter attached to the battery.

The alignment is fine by the way, because we have achieved a bit of a turn.

Exide 80 amp 6 months old. It measures 6.4 volts and when the starter is energised, the Bendix throws in nicely with a hefty clunk and there was a tentative turn of the engine and throughout the operation the (analogue) voltmeter didn’t drop below 6 volts.

I’m hoping it’s just the fact that I’m using jump leads (2000 amp) and once I’ve connected up everything all will be well, but it sounds like it simply hasn’t the grunt to turn it over...I can assure you the compression though good isn’t that good!

Thanks for allowing me to piggyback on this thread John and for everyone’s help, I’m now going to crack on with welding up the dashboard which had a huge valve radio jammed in the glove box!