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MG MGB Technical - Starter

I have a 1980 mgb and I'm having problems with my starter. It starts fine but after l drive it for 15 minutes or so and the car is warm the starter engages . After that happens when I turn key to the start position the starter will disengage as long as I hold it there, as soon as I let it go the starter will engage again. Can someone help me?

Gary
Gary J Callea

Where are you located?

S

Sounds like ignition switch or starter relay.
Allan Reeling

I concur with Allan. My first ignition switch literally came apart inside the cylinder. You could turn the key 360 degrees. We had to remove all the wires to the switch and "hot wire" the car to get it home.

Cheers,

Gary
79 MGB
gary hansen

Gary-
It's the ignition switch, not the relay. . It is prudent to remove the Negative (-) battery cable from its post terminal before you get near the wires that are underneath the cowl. In order to provide sufficient clearance to permit the removal of the cowl, lower the steering column a quarter-inch by loosening (preferably not removing) the three 9/16" hex bolts that hold the column to the cross-beam that is underneath the dashboard.
Next, you need to remove the cowl by means of the use of a screwdriver that has a PZ2 bit in order to remove the PosidDrive screws from the side. The cowl is held together by two obvious PoziDriv 10-32 screws that are designated by red dots on the left side of the steering column which are easy to remove, but there are also two shorter PoziDriv 10-24 screws that secure to cowl to the steering column. These are designated by blue dots on opposite sides of the steering column that hold the end that is furthest from the driver. These are commonly rusted to their captive nuts, so soak them overnight by means of the use of a good penetrating lubricant such as Liquid Wrench or, better yet, a home-brew 50/50 mixture of acetone and automatic transmission fluid prior to attempting to remove them. Afterwards, replace them with stainless steel PoziDriv screws, and apply a thin coating of LoctiteŽ Marine Grade anti-seize compound onto their threads. Be aware that a Phillips-head screwdriver does not work well in a PoziDriv screw as it tends to cam outward and chew up the screw head. A Phillips-head screwdriver has an angle on its flanks, a pointed tip, and rounded corners. A PoziDriv screwdriver has straight-sided flanks, a blunt tip, and additional smaller ribs at 450 to the main slots. The PoziDriv configuration was designed specifically to allow much greater torque to be applied because of its more positive engagement. These PoziDriv screws are tricky to remove without first lowering or removing the steering column, and even trickier to replace. If loosening the three 9/16" bolts that are located beneath the steering column in order to lower the steering column does not provide sufficient clearance to permit their removal, then remove those three 9/16" bolts, and then drop the steering column into your lap in order to give you complete access. If you remove the 9/16" bolts, then be aware that there are alignment spacers between the steering column and the captive nuts above. Be warned that dropping the steering column will both stretch and stress the wiring loom (harness) of the switches, so you are trading one challenge for another!
The cowl lip that goes under the steering wheel makes it necessary to bend the cowl a bit. Due to the plastic having become somewhat brittle with age, the cowl might tend to crack. Be warned that new cowls are No Longer Available. I recommend using a hair dryer in order to heat the cowl to the point that it becomes more supple. The two halves may be taken off sideways. If not, the trick lies in bending both of the halves of the cowling slightly at an outward angle at their farthest ends from the steering wheel until its internal baffles (for lack of a better word) have just enough clearance so that it will just slide over the body of the steering / ignition lock when moving them towards the sides.
Note that in the large-diameter section of the upper steering shaft there are two keyway slots that are 1800 apart. These are present for locking the upper steering shaft, so make sure that the steering wheel is centered in the locking position of the upper steering shaft so that it does not bind the locking mechanism, thus hindering removal. See that rusty-looking flat thing on top of the mounting clamp? There are two of them, and they are what remains of a couple of shear-type anti-tamper screws (Moss Motors Part # 263-700) that keep the steering lock / ignition switch assembly clamped onto the steering column. These are 5/16"-24 UNF X 1/2" if it is SAE, or 8mm by 1.25mm by 20mm if it is Metric. You can either notch the anti-tamper shear screws by means of the use of a Dremel tool and screw them out counter-clockwise (anti-clockwise) in order to remove it from the steering column, or you can drill them, and then back them out by means of the use of an E-Z-Out tool if there is not enough remaining of them to permit notching. The top and the bottom halves of the mounting clamp should then separate. On 1974 through 1976 model cars, remove the press-fit pin that is located in the hole for the anti-tamper shear screw (if you can), and then retract the tumbler mechanism from the lock assembly, leaving the steering column lock and the switching drum unit in place. Thankfully, on 1977 through 1980 model cars, a set screw (grub screw) superseded this press-fitted pin. Afterwards, you can take the tumbler mechanism to a local locksmith. Several different suppliers of this device were utilized, even within the same model year. How disassembly is performed depends on the specific lock. The mechanism is quite complex, and it is full of tiny parts and springs. Things can easily go flying in all directions, so let a skilled locksmith deal with it properly. Upon reassembly, the damaged shear-type screws can be replaced by means of the use of either flat-head hexagonal bolts or Allen-headed screws.

If the switching drum unit proves to be faulty, it cannot be repaired. On the bottom half there is a very small #2 PosiDrive set screw (grub screw) that secures in place the small plastic switching drum unit that contains the electrical switching system. Note that Chrome Bumper models have the switching drum unit secured in place by two #2 PosiDrive set screws (grub screws), while the Rubber Bumper cars employ only one #2 PosiDrive set screw (grub screw). The earlier, large-diameter switching drum unit employs five individual bullet connectors, while the 1974 and later small-diameter switching drum unit employs a single multiplug connector. Remove the set screw (grub screw), and the switching drum unit will then slide out, leaving the steering column lock in place. It is keyed, so it can only be re-installed in the correct orientation. Be sure that your replacement switching drum unit is appropriate for the wiring of your model year car, as there were differences.
Stephen Strange

Wow excellent write up Mr Strange!

S

We get that from Steve, Steve
When He says something , you get the lot and usually it's spot on.
Magic isn't it---!

Cheers
willy
William Revit

"It is prudent to remove the Negative (-) battery cable from its post terminal ..."

Take extreme care when removing a battery cable.

With the MGB you really need to remove the earth/ground cable first - regardless of whether the car is positive earth or negative earth, twin 6v or single 12v, and replace it last. Being accessed through a hole in the rear shelf it's very easy for a spanner to touch the body when working on a battery post, particularly with the later clamp-type connectors.

If you are working on the 12v post when this happens and haven't already removed the earth cable then you will short out the battery with predictable results.

If when removing the earth cable first if your spanner should happen to touch the body then nothing will happen as that battery post is already connected to the body.

Once the earth/ground connection has been removed you can then remove the 12v connection safely. For if your spanner should touch the body now there is no path for current to flow as the earth/ground connection has already been removed.
paulh4

Gary lives in upstate New York
Mike Plumstead

Yes magical!

I've had the same experience with one of my past cars.

I do not think I could have written up the help that Stephan Strange wrote here.

I was impressed at what a great job he did with his descriptions!
S

Steve-
The above was merely a Copy & Paste from the text of my book on the MGB. If you'll post your Email address, I'll send you a copy of it as a .PDF file attachment.
Stephen Strange

When Mr Stephen Strange says-
"The above was merely a Copy & Paste from the text of my book on the MGB.",
what he doesn't say is that his book on the MGB B-Series is the most comprehensive that I have ever seen.

If you send Steve an up-to-date copy would you mind sending me one too Stephen as my copy is now a few years old and I am looking forward to reading the latest updates.

Cheers
Colyn
Colyn Firth

Hey Steven!

Would love a copy! My email is sdevine17@comcast.net
S

This thread was discussed between 18/03/2019 and 24/03/2019

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