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MG MGB Technical - Starter solonoid

A year ago I was grateful for advice from members concerning the starter relay on my 76 roadster. I now get intermittent problems with the starter motor not turning over. I've taken off the plastic cover and checked and cleaned the connections. ( by the way, I found the only way to get the cover back on was to warm it up with a hot air paint stripper ) But it still happens, though thankfully if I keep turning the key it eventually cranks it.
Now I'm pretty certain it's the solonoid as the ignition light stays bright, and I can hear the relay clicking. Can the solonoid be repaired and is it DIY. And can I remove the starter without removing the dizzy like it says to do in Haynes.
c cummins

No reason you should have to remove the dizzy, but it'll be a bit of figuring out exactly which way to wiggle it out - I had it angling downward and removed it from below, and it was a tight squeeze.

I know the starter solenoid can be worked on, and parts for it are mostly available, but the task of figuring out exactly what's wrong with it (when the problem is intermittent) combined with the rather unpleasant construction of the solenoid assembly may make it worthwhile to simply exchange for a complete rebuilt unit. The rebuilt starter is neither rare nor expensive.

Since you've sorted the relay I'm assuming that the solenoid truly is getting voltage every time you turn the key... verify before buying anything.
Sam

Your problem could still be the relay. With the ignition on (after pulling out the wires from the relay to solenoid) jumper the leads to see whether your starter engages. I had a recent problem with my starter relay. It was clicking okay but by bypassing it I was able to spin the motor. I changed the relay and everything is now okay. However on opening up the relay box the relay and its contacts were in very good condition so why it was not engaging the solenoid I do not know.
hope this helps.
willyphixitt
W A Nixson

As Willy says unless you can hear the solenoid 'clonk' when you turn the key and get no 'whirr' from the starter, it could still be the relay, or the connections at the relay or the solenoid.

You must do some proper diagnosis with a voltmeter on the brown/white between relay and solenoid to determine whether voltage is not leaving the relay, or not arriving at the solenoid.

If you have voltage on the brown/white it is not the relay. If you don't it is the relay or the connections of that wire or the brown wire, even though you can hear the relay clicking.

If you have voltage on the brown/white then check again right on the spade at the solenoid. If you have voltage there as well then it is the solenoid - if the solenoid doesn't clonk.

If the solenoid is clonking then it is the solenoid contacts or the motor brushes, commutator, or broken sections of rotor wiring. Sometimes you can get a meter on the copper link between the solenoid and motor to determine which.

Solenoids windings can fail, unless you can find a bad connection to spade or body there is not much you can do apart from replace it. V8 starters are prone to solenoid failure as one of the exhaust down-pipes runs close by and causes heat damage, but that shouldn't happen to a 4-cylinder.
Paul Hunt

I had a similar problem recently where mine would definitely clonk but the engine wouldn't spin. I removed the starter (it is a tight squeeze) and removed the solenoid and found the copper contacts in it were well worn out. It was easy enough to take apart from memory. A replacement solenoid was surprisingly cheap and easy to fit so it wasn't worth messing about with the original. The replacement turned out to be made in Japan!

Simon
Simon Jansen

Thanks for the help, it is behaving itself at the moment, but always looking for a unobstructed slope to park on just in case is annoying. So I think I will take Simons advice and strip the solenoid down.
c cummins

Hi
If you are going to the trouble of removing the starter to check the solenoid out I'd be having a look at the brushes while it's out as the solenoid gets it's earth through them. Cheers Willy
WilliamRevit

Willy - I don't think so, the brushes power the motor rotor. The motor stator and the solenoid get their earth from the body of the starter which is bolted to the engine of course.

The brushes (and comm) *could* be at fault of course, but that would result in a non-spinning motor even though the solenoid had clonked, the same as when the solenoid contacts are bad.

Taking the original post at face-value (always risky ...), the solenoid isn't clonking, so the problem could still be with the relay, the solenoid winding, or the connections to each and not the motor itself.
Paul Hunt

I too have had a sudden problem starting my 74 MGB GT. It has been running well but yesterday didn't want to turn over. My first thought was the battery had gone flat or because of the amount of heavy fog a contact had failed. I checked the battery contacts and they were clean and bright. I cleaned them again anyway. Car still didn't want to spin the starter. It acted like a low battery. Eventually the car started and I drove it to the next community to work and it ran well and lights etc were bright but when I stopped and tried to restart it had the same symptoms (so I parked on a hill) After work went through the same routine and it eventually fired up and ran well but upon return home wouldn't turn over again. I bypassed the starter relay to check that out and it acted exactly the same. The battery appears to have plenty of power, all lights are bright and alternator light dims slightly when trying to crank the engine but does go out if the car starts.

Does this sound like a solonoid or perhaps starter?

Brian
Brian Smith

I have had similar trouble with my starter not turning over the engine. Until I get a chance to look at it I keep a 1x1X30inch stick In the car. If it does not start I just pop the hood and tap the starter 3 times and it will then start right up. It sure beats trying to push start it! Bob
Bob Ekstrand

What happens to the interior light when it won't crank? If that only dims slightly when the starter won't turn the engine over that indicates the battery and its connections are OK. If these were bad it would go out or dim right down.

The alternator light gets its ground from the engine whereas the interior light gets its from the body, so a difference in these two could indicate a bad engine ground. Connect a voltmeter between a known good body ground and the engine, and voltage shown while cranking is voltage lost in the engine or gearbox earth/ground strap. Note there will always be some, but ideally only a couple of tenths of a volt. half a volt or more is worth investigating.

If they both react the same it could be bad connections at the solenoid, specifically the battery cable making good connection to the brown wires, but not to the solenoid stud. Note that this would only happen on the later starters - like the 74 - where the battery and brown cables are all bolted to the stud. If thats OK it could be bad solenoid contacts as mentioned before, or worn or dirty motor brushes and commutator. Some starters have an exposed link between the solenoid and the motor which would allow you to get a meter probe on it and so determine whether the solenoid contacts were at fault (low voltage on the link) or the motor (normal voltage on the link)
Paul Hunt

Bob, sounds like the MG owners equivalent of tapping the heels of your ruby slippers together three times and saying "There's no place like home... there's no place like home" :)
Simon Jansen

This thread was discussed between 27/11/2008 and 05/12/2008

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