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MG MGB Technical - Starter and electric gremlins..


Rather long winded:

Finally got round to installing the new starter from Moss yesterday. By now I am getting a bit of an “expert” at this with an extra pair of hands from a friend of mine. It came out quickly and the new one went in just as easy. Thought I was winning until I turned the ignition key and my heart dropped when all I got was the usual clonk from the solenoid. Was ready to hit Wigan with a big hammer out of thrustration. We fiddled around with battery connectors and finally it fired up…. But……

When Wigan started there was this horrible noise and loud humming sound coming from the starter, it was particularly loud as the top was down, bonnet up and in the garage. So I turned the ignition off. Then turned it back on again and “clonk”. Waited a little and then fired Wigan up again, same noise again. I was about to turn the ignition off again and I just touched the key as to turn the ignition off. The loud humming noise stopped, the engine didn’t sound as though it was racing etc, rpm’s went up etc. Wigan sounded perfect. All I can think of is that the ignition switch itself is faulty and not disengaging as it should. So now Wigan is “back” on the roads. Its fine as long as I turn the key back ever so slightly after cranking. I will be placing an order for one today, but in the meantime it stays where it is for the time being as I do not want to fry this one!.

I think the one I got from Stowe was perfectly good and that there are other issues going on, which I hope I am on the right track for. When I got under the car to take the starter out I noticed something odd about the solenoid. When I got it out I noticed that there was a lot of corrosion and burnt stuff around the solenoid ground, at least that is what I think it is called. Something must have fried it and if I can get to the bottom of this, it may help me to get a better idea of why I have had to put three starters in since early summer. This what has happened:

The original starter. Driving home top down car started to sound very odd, even my wife pointed it out. Got home, stopped the car, started, drove down the road, parked, went back… clonk clonk… push start and home

Replaced this with a starter out of my parts car.. Sounded ok at first but soon afterwards started to sound very weak. Had to crank quite a few times to get it to fire up. Eventually clonk clonk

Replaced this one with the starter from Stowe. Immediately after install the starter gave this loud whizzing squeaking noise when fired up but would stop immediately after the starter “supposedly” disengaged. Started up in the back one day with the usual sound which stopped when the starter disengaged, but then the car started to make this loud squeaking noise, wife came out again and asked what that noise was couldn’t tell if it was the loud humming noise which I heard yesterday, as I was not in an enclosed place etc like I was yesterday. Stopped the car and decided start it up and put in the garage but .. clonk clonk

The new starter issues as reported and the Stowe one fried.

Am I on the right track?
GG Ginty

Maybe. Your thought seems to be that the starter is not being turned off after the engine has started and is, in effect, fighting the engine. The starter wants to turn at some certain speed while the engine is being required to operate at various speeds. Is this a correct synopsis of your thoughts?

It is interesting that you note the name you have given the car (I am assuming that Wigan is the name of your car) but have not reminded us of the year. Knowing the year could be important as part of the diagnosis procedure.

Assuming that you have something other than a Mark I, because you mention having to manually return the ignition switch to the run position, it should be possible to check and see if power is flowing to the starter solenoid when the engine is running and the ignition switch has not been manually moved to the run position. If there is power flowing, then the starter is working against the engine and that problem should be corrected. If you have a starter relay, check for power flowing to the relay from the ignition switch. If there is, manually turn the ignition switch to the run position and check again. If this corrects the problem you need to consider replacing the ignition switch. If power is not flowing to the starter relay, but power continues to flow to the starter solenoid, you have a bad starter relay.

Burned contacts are either the result of poor connections or too heavy a current flow. But, Paul Hunt or Dave DuBois should be along to discuss this in greater depth and tell you how to check that aspect of the system out. I just look for loose connections and loose wires myself.

It should be fairly easy to check and see if power is flowing to the starter, keeping it engaged after the engine is running and the ignition switch has tried to return to the "run" position after being held in the "start" position. When you can confirm that the starter is, in fact, engaged and running all the time, the rest of the procedure becomes routine testing to find the source of the current energizing the solenoid.

Les
Les Bengtson

Thanks Les, mine is a 74B

GG Ginty

Then, I believe that it has a starter relay between the ignition switch and the starter solenoid. This can be confirmed by looking at your wiring diagram. If so, it will be one other source of power to the starter which will have to be checked out. Relays have been known, as they age, to stick in the on position even when the switching power going to them has been terminated.

Were it my car, I would start checking for power to the starter at the starter solenoid. If you have power at the solenoid, with the ignition switch in the "run" position and returned to that position by the switch itself, manually turn the switch to the run position and see if the power flow stops. If so, bad switch. If there is power to the solenoid and there is not power from the ignition switch to the starter relay, the relay is staying energized and should be replaced--the generic ones available at most auto parts stores seem to work fine for this application.

Please let us know what you find out. If you do need to replace the ignition switch, try to find a good, used one. The new assembly I installed on one of my 79s only lasted a year before the key became impossible to insert and turn. Moss does not accept returns of electrical parts even when the root of the problem is the mechanical portion of the system.

Les
Les Bengtson

That's dead on description of switch/lock failure, fairly common. New ones are awful. I take them apart, new or used, and carefully clean everything, paying special attention to casting flash and machining swarf, of which there is usually plenty, especially in new ones.

Another thing that has exactly the same effect = DOA starter and burnt wires, is shorting between the various wires in the bundle going to the solenoid, caused by the (formerly!) rubber boot over the starter. Examine carefully, especially since you have had problems, but this problem is the switch/lock mechanism. And it is usually terminal if anybody but you drives the car!

Les, it's just like blueprinting a gun, lots of careful file/scraper work, cleaning, testing, lubrication.

FRM
FR Millmore

If you just touched the key and it disengaged then it is the ignition switch that is at fault. There was a spate of this a while back on some modern Eurobox or other, and several fires as a result which the manufacturer initially refused to fix under guarantee saying the driver should have realised the key wasn't coming back like it should do!

It's quite possible this has been happening for a while, and has wrecked all three motors.
Paul Hunt

Thanks... I think I am (finally) on the right track. Just have to figure out which switch I need. Also I have heard that if one is just replacing the switch one does not have to remove the lock/key setup, screws etc????
GG Ginty

That's the theory, the two are usually available separately.
Paul Hunt

This thread was discussed between 16/11/2009 and 17/11/2009

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