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MG MGB Technical - Key turns but no crank

I have been having an intermittent problem starting my 1977 MGB. When I turn the key the ignition lights come on but the starter does not crank the engine. I am thinking starter or solenoid. Any ideas or thought would be greatly appreciated.

Thanks,

Kelly
Kellya

Kelly. You have touched on the most probable problem. The solenoid and starter are a single unit rather than the two units used on some of the earlier cars. The change was in 68 with the Mark II series and four syncro gearboxes.

One thing to do before removing the starter and taking it in for testing is to check all of your electrical connections to make sure they are solid and firm. I had a similar problem when the old connector on the wire coming from the starter solenoid was quite loose fit on the spade terminal of the rebuilt starter. A new push on connector, which fit the smaller spade connector properly, has made the starter reliable.

You might also want to check for voltage at the main terminal of the starter as you are cranking. A bad connection at the battery or a bad cable from the battery to the starter can cause the problem you are describing. But, if the connections are good and you are seeing 11.5 to 12.5 volts at the main terminal of the starter when attempting to crank it over, you will need to pull the starter and have it tested.

Les
Les Bengtson

Kelly - You also have a starter relay up on the right side inner fender that could be creating the problem (although as Les stated, the solenoid or starter are the most likely cause). For a good diagram of the wiring for your car, go to http://www.advanceautowire.com/ click on stock schematics and scroll down to the diagram for your car and print it out, or better yet, copy the file on a flash drive, take it to Kinko's and have them make a full size (14 X 17 I think) copy and laminate it. This will make troubleshooting electrical problems much easier. Cheers - Dave
David DuBois

Is there a loud clicking sound when you turn the key? This is the solonoid moving in and out. If so it's probably the main solonoid contacts or the motor itself. If no clicks then the solonoid could be at fault, or just a connection problem from the starter relay. If there is a soft click this is the starter relay, there are 2 or more on the right inner wing, get someone to listen while you turn the key. If no detectable click then it could be the relay or the ignition switch itself, or intervening connections.
Al

Repeating some of what has been said above. A 77 should have a starter relay, and with the bonnet up and the doors open you should be able to hear that clicking, the solenoid clonking, or the motor whirring if it doesn't actually tuern the engine over.

If you don't hear a click then you need to check the white/red from the ignition switch to the relay and the black earth at the relay with a volt-meter. With the key turned you should see 12v on the white/red, if you don't you need to move back towards the ignition switch. If that shows 12v check the black, and that should show 0v. If it shows 12v or approching it then the grounding point for the relay is bad. If the white/red shows 12v and the black shows 0v then the relay winding is bad.

If the relay clicks but the solenoid doesn't clonk then check the brown and brown/white terminals on the relay. The brown should show 12v all the time, the brown/white should show 0v normally and 12v when you turn the key. If the brown voltage drops then there is a bad conenction back towards the solenoid. If the brown/white doesn't rise then the relay contact is faulty.

If the brown/white goes up to 12v but there is no clonk from the solenoid check this wire down at the solenoid.

If the solemnoid clonks but no whirr from the motor then either the solenoid contacts are bad, or the motor brushes/windings are bad.

Test component spades and wire connectors in all cases, to reveal bad connections i.e. different voltages between them, and all the above assums component wiring hasn't been disturbed and put back on the wrong terminals.
Paul Hunt

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This thread was discussed between 03/07/2009 and 31/07/2009

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