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MG Midget and Sprite Technical - Intermittent Starter on 1500 Midget

Most times the car will start ok with the starter motor acting as it should.
Occasionally it barely turns the engine over such that the car cannot start.
Did it today. Started OK went for a 5 mile journey parked then returned. Would not turn over, well barely and not enough to start the car. The car is fitted with an ammeter which does show a big charge after such incidents.
Left 10 minutes and then it did start.

The motor was checked and pronounced very OK a month or so back by a specialist starter motor firm.

Any ideas?

George
G R Wilder

George.
As a baseline starting point, check, clean, tighten all the starter circuit connections.

Especially.....

Body earth strap and solenoid to body earth (an old favourite).

If it happens again you could immediately lift the bonnet and feel your choke cable. If it's hot it's a sure sign of a poor earth.

Good luck.
RS Hughes

I would be looking for poor earth connections at the battery and engine. Followed by a set of brushes in the starter motor and possibly a new battery.
If you have the opportunity and a meter, check voltages at the battery, starter motor supply (both sides of the solenoid) and starter motor case. Whilst cranking all should be battery voltage except the last one which should always be zero!

Best of....
MGmike
M McAndrew

Following a rethink.

The solenoid is working because the starter turns - even if it's slow. So it should be okay. If the solenoid or it's primary side earth connection were bad it probably wouldn't even try to turn the starter.

Battery should also be okay as it usually works. This is not completely a given as batteries can behave differently under high and low current demands, but probably fine. Places like ATS, Kwik Fit etc will usually test your battery for free - it only takes seconds.

Starter similarly should be okay. It turns even though it's slow sometimes and it's been recently checked out and passed okay so can be assumed to be good.

So it's the high current starter circuit you need to check first.

First, battery pos pole clean and tight.
Then the two big connectors on the solenoid clean and tight.
Then the big connection on the starter, again clean and tight.
Then the engine to body earth strap (C&T). This is often the culprit BTW.
Then the body earth to battery neg pole. Clean and tight.

If all connections are good (bare metal connections to the body etc) and cable conditions are good you have a baseline to look elsewhere, but these things are essential to check before looking for big faults elsewhere.

As MGMike suggests a voltmeter and a glamorous assistant would be helpful.

Oh and check the starter mounting bolts. If they're slack it can result in a high resistance to earth just like a loose cable.
RS Hughes

If as you say the ammeter is showing a heavy current recharge then something has been taken from the battery or it is not reliably holding its charge.

So when you try to start it, current must be flowing to the motor to deplete the battery, but the motor is not responding correctly. Bad connections would not allow current flow so the battery would not necessarily lose much charge.

I would still suspect the starter motor and/or the battery.

Can you borrow a battery and carry it in the boot with jump leads to hook up if it happens again, to eliminate the battery, if it doesn't make any difference?
JB Anderson

All
Thanks for your very considered replies

All the contacts will be checked and rechecked and hopefully some voltage tests too.

Afraid I made an error in my first posting - forgot to put the word "not" in the sentence about the ammeter.
It should read;- The car is fitted with an ammeter which does NOT show a big charge after such incidents.

George

G R Wilder

Good luck George.

BTW I should have mentioned it's a good idea to disconnect the battery while you're checking the starter supply wiring and connections, particularly the permanent live pole on the solenoid. Just to prevent any fireworks!

You need to disconnect them anyway to clean and check them, so now's as good a time as any :-)
RS Hughes

Mine was like that; brushes were worn.

Brushes cheap.
Motor comes apart easily.
Brushes slide in easily.
Very oily under the car to remove but two sockets and a spanner sorted it.

BUT: needs a very good soldering iron. (I had an old heat it on the gas stove one with a big lump of iron on the end. It was terrific once I found it).
Dave Squire

Dave
Starter out and bench checked by local starter motor rebuild firm - all OK.
Starter worked OK but will it continually - only time will tell with an intermittent fault.

All earths etc have been checked too
George
G R Wilder

Have they looked at the brushes? There is a min length for them. Mine still spun when out but not when in (presumably not good enough contact when brushes reach a critical length).

I have two starters and the other failed soon after (hence the fixing). That has the same problem.

Original starter with new brush set just fine.
Dave Squire

Good point Dave. Especially given the likely age of the starter. I suggested going through all the connections mainly to eliminate them from the inquiries since they are simple easy checks.
Once they discounted I agree the next place to go is the brushes.
Greybeard

This thread was discussed between 12/06/2015 and 26/06/2015

MG Midget and Sprite Technical index

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