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MG MGA - Starter Motor Brushes

I have started having intermittent starter problems. My initial investigation focussed on the starter switch and I discovered that I could not get enough pull on the starter cable to guarantee contact in the switch. That is now resolved.

But I now appear to have a second problem. Sometimes the starter will turn, sometimes not, regardless of whether I pull the cable or manually push the starter switch shaft.

Yesterday it was not working so I rotated the starter shaft about 1/4 of a turn with a spanner. The motor then spun up quite happily. When it spins it revolves at the normal expected speed.

I took the motor out this morning (another oil filter confined to the bin!). Inspection showed the motor to be clean and plenty of life in the brushes - which I would expect as the motor is only 2 or 3 years old. However, the wiring on one of the 2 unsheathed brushes showed one wire badly damaged - possibly electrical burning but I am not sure. The broken strands were touching the casing. Is this okay? The other unsheathed brush and the 2 sheathed brushes were absolutely fine.

Picture attached.

Help

Steve


Steve Gyles

Steve, does it look like the wire was burned or physically damaged? If it burned, you may have short circuited or earthing windings on the armature, giving you that dead spot. The brushes don't look worn out, are they free in their holders?
Lindsay Sampford

Lindsay

They looked free in their holdings.

I have never had the motor apart before, so if it was physically damaged it was done in manufacture assembly. My first impression was that it was electrical damage. However, the unsheathed brushes are earthed to the casing so I fail to understand how shorting could be an issue. That all said, I am not genned up on electric motor wiring, hence my plea for help.

You are good on this 'standard' sort of thing. All suggestions and guidance for anything else to check are very welcome. I do have my testing meter with me in my emergency pack-up. One item not in storage. Mind you I had to go and buy an oil filter removing tool.

Steve
Steve Gyles

Steve,
The wires are redundant, and you should just cut off the frayed wires. Chances are they were arcing to ground. If you're concerned, go to the local hardware and buy some "Liquid Electrical Tape" and coat the wires after you trim them. It works great.
Mike Parker

Steve, I am talking about a shorted winding in the armature. This would pull a lot of current through the brush wires while you were hanging on to the starter knob and may have fried some of the strands. The only other things I can think of that could cause a non-op of the starter would be a dead segment on the commutator, stuck brushes or a jammed Bendix. I think you would have felt the latter when you turned the motor shaft. I think you may be looking for a replacement starter Steve.
Lindsay Sampford

Steve,

I had the same intermittent problem with my starter last year. It was finally determined the likely cause was the brushes were sticking in the holders. After disassembly and cleaning the whole thing it has worked fine for 18 months.

The brushes seemed free but were apparently occasionally sticking enough to prevent contact.

Jim
Jim Ferguson

Such damage is usually the result of (last guy's) attempts to pull the brush out with pliers or a hook. The springs are strong and the wire fragile, and if you don't pull straight or if the brush is stuck, you get this. I finally learned to pull only on the brush spring with a hook, and only touch the wire with fingers - but they do not fit in there very well! If the broken wires stick out, clip them. If any strands were shorting, they will have little balls melted on the ends. Make sure any insulting paper is in place, especially the one that goes under the steel band across the windows. The "dead spot" is/was either a stuck brush or a bad armature, which can be tested by an electrikian.

FRM
FR Millmore

Thanks guys. I got very much the same advice when I spoke to Bob West's team.

The trouble with this sort of problem is that it requires a new oil filter every time I pull the starter, plus all the oil down my arm! My back is also not good at the moment so I don't want to lie under the car any more than I have to. The fixes suggested, although sound and likely to work, still have a bit of hit and miss element about them and I only want to do the job once at the moment. After a full risk assessment I am, therefore, going to install a new unit and sort this one out in slower time when I have my full workshop back - and the back has eased!

Bearing in mind that a new starter is 39 + vat + postage there comes a point when renovating old parts does not make economical sense. If I take the old unit (not original item, just Lucas NOS) to a reconditioner/electrician to have the unit checked out and repaired I will have probably paid more than the cost of a new unit. Food for thought.

Many thanks

Steve
Steve Gyles

Steve, it's probably worth trying your local Motor Factor (not Halfords!). We have one here in Newmarket that, if they don't have it in stock, "will have it by half-past two mate", (they've even dropped things in at my house as they've been going past!). Surprisingly, these people are often able to supply even the more obscure parts for old vehicles (I walked into ours and came out with an MGA brake light switch with the proper screw terminals, straight off the shelf!) and at a cheaper price than Moss etc, plus you get it straight away and don't pay inflated shipping costs. Might be worth a look in yellow pages and a couple of 'phone calls Steve.
Lindsay Sampford

Cheers Lindsay

I agree with you about local motor factors. I have yet to locate mine in Farnham. I had fun going through all the oil filters in Halfords to find the right one for my spin-on adapter that uses a Ford Escort variant. They don't keep a cross-reference to all the other manufacturers so it makes it difficult getting bits from them. You get asked questions like: "What's the registration of your Escort mate?"

A lesser known fact is that the brake cylinders are the same as the Morris Minor and cost less at motor factors.

I actually ordered my starter from Bob West. He gets most of my business as he is always so helpful with advice when I need it. I look on it as a preferred supplier arrangement, whereby we both win.

Steve
Steve Gyles

So much for my analysis! I have just fitted the new starter motor. Same problem! I convinced myself through various checks that it was the motor but it now seems it has to be the starter switch. My first switch went wrong a few weeks back and Barry Gannon kindly sent me a used but serviceable original Lucas switch. It now seems it must be the suspect item. There is nothing else it can be. I carried out a continuity check on it with my meter but I guess it's not making a good enough contact for the high load that is needed? Could a problem with the original starter motor have caused overheating/ burn out in the switch? Advice on this one please.

Ho hum. I gather the new ones are not much good either but I have no choice. My two other old stock items are in storage. I need to get my house purchase sorted!

At least I now have a spare serviceable starter motor?

Steve
Steve Gyles

Steve, I've been using an ebay starter switch for 2 years now - so far so good. Good luck with your search for a 4 car garage with attached house - cheers Cam
Cam Cunningham

Steve, If I understand you, when you pull on the starter switch the starter motor does not turn at all. I had that happening and traced it to a bad battery lead to the starter switch under the bonnet. The cable lead was corroded inside the cable and causing huge resistance. I replaced the cable and no more problems. Just a thought.
David Holmes

Hi all

I feel such a twat. I have ignored the good advice that has been posted so often on this forum: to disconnect the starter motor cable from the switch and touch it to the live cable. Hey presto, a fully spinning starter motor each time. Dud switch definitely. I should have done it days ago and saved the cost of a new starter.

Steve
Steve Gyles

Been in reflective mood for the last hour thinking about my lack of correct diagnosis by not following a logical process.

That said, I got to wondering why the switch failed in such a relative short time; a sort of chicken and egg situation as follows: Was it through not making proper contact within the switch because the starter pull system reached an end stop too early (other thread); was it because of a failure within the starter motor causing overheating (when nothing happens with the starter knob pulled you tend to keep pulling harder and for longer); or is it simply an item that is not fit for purpose and will not take the electrical loads?

Might ask Bob (turbo midget) to post chapter and verse on his system.

Steve
Steve Gyles

Some current replacement switches, the ones with white insulators, may have poor construction and may fail early. see here: http://mgaguru.com/mgtech/faulty/ft004.htm
Barney Gaylord

Steve, these are the people for a starter switch. http://tinyurl.com/38csbr8 Don't get one with the white nylon base.
Lindsay Sampford

Lindsay

Just got my new starter switch from Bob West. It looks the same as the one in your link. Similar price. It's not white nylon. Works fine.

Steve
Steve Gyles

This thread was discussed between 22/09/2010 and 28/09/2010

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