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MG MGB Technical - Engine doesn't turn over

1977 mgb roadster, starter is not turning the engine over.

I pulled over after a 10 mile ride to take a call. Engine would not turn over. Made the "clicking" sound when turning the key as if the battery was discharged which I thought was odd since I had just driven 10 miles. A jump didn't change things.

After getting the "ride of shame" home I charged the battery and still no turnover. My charger said the battery was fully charged as did a multimeter check when turning the key.

So I thought starter is bad. After new starter and new starter relay it's still not turning the flywheel and is making the same noise. I'm about to replace the battery but without great expectations.

Any and all ideas and suggestions would be greatly appreciated.

Thanks.
Brian Denis

Before I replaced that battery I'd check that the starter motor has a good ground. Use your jumper cable to go directly from the starter motor frame to your engine block. Let me know what happens.

Jud
J K Chapin

“ Use your jumper cable to go directly from the starter motor frame to your engine block.”

That’s assuming that the engine block has a good ground.
Dave O'Neill 2

JK & Dave, thanks for the input I'll do that first thing tomorrow.... it's dark here now.

Unfortunately JK I was too quick on the draw, $200 USD later I'm sure it's not the battery. I got 1/3 of a revolution of the flywheel one time before replacing it which pointed me back to the battery. Your idea of a lousy ground is a good possibility.

My latest (and perhaps last) suspect is the ignition switch. For a while the switch operation has been clunky. I thought it just needed graphite but while turning the key, unless I was being neurotic, I thought I smelled burning. Any ideas on how to check the white/red wire going from the switch to the relay?

I really appreciate the help.
Brian Denis

I don't know anything about ignition switches so I let others address that. As to Dave's excellent point, try it first with just a cable between the starter motor and the block. If that works - good. If not, leave the cable between the starter motor and the block connected and use the other cable to go from the block directly to the earth post on the battery. If that doesn't work then just always park on a down hill :-)
J K Chapin

If you turn the key to start and hear a single click each time that is almost certainly the starter relay (one of two on the inner wing) you can hear, which means the ignition switch is probably OK.

But if you hear rapid clicks while the key is turned that means insufficient voltage is reaching either the relay or the starter solenoid, you need to find out which it is by feeling them while someone else turns the key.

If the engine (CB) or gearbox (RB) earth is bad there are usually enough alternative paths via accelerator, choke and heater cables to get some movement from the starter.

As you have a multi-meter connect that between the battery cable stud on the starter solenoid and a body earth and you should see battery voltage, what does that do when you turn the key to start? If that drops right down there is a bad connection in the battery earth cable to body or 12v cable to the starter.

If that still shows battery voltage connect the meter between the engine block and the body and do the same. That should show zero normally, but if it goes up more than 1v when turning the key to start then you have a bad gearbox earth.

If all good so far then connect the meter between the solenoid operate terminal (white/brown or possibly white/red, not the thinner white/light-green) and again turn the key to start - wiring still connected! That should go up towards battery voltage - typically 10v when the engine is turning over and everything is good. If that's not happening then you need to look at the starter relay. If you still have the cylindrical ones they are known to fail (even if they click), replace it with a 30 amp Bosch cube-type which the factory were using right at the end of production.
paulh4

So, I have a diagnosis but not a cure as yet.

Following all of your suggestions I tested the voltage at the solenoid hub w/o starting, 12.5. Tested it while the key was turned to start, 1.8, yikes!

Jumped from the battery negative post to the starter frame and it turned over, yay! Jumped from the battery to the body, no go. Jumped from the body to the engine and it turned over. So my problem is the grounding of the motor.

Paul, even though this is a RB car I have a grounding strap running from the motor mount bracket to the body. I'll replace the strap and clean up the contact surfaces and hopefully be good to go in finishing the driving season.

Gentlemen, I don't know that I ever would have considered the ground as a culprit w/o your assistance, so thank you!
Brian Denis

Good to hear that you’ve found the cause of the problem.
Dave O'Neill 2

It's not uncommon to have an engine earth strap on RBs, the gearbox strap is a right pain to deal with compared to the engine strap on CBs!
paulh4

Epilogue: "The rest of the story" or "How a 20 year old bodge came back to bite me".

So referencing the sad tale noted above I'm happy to report my 1977 MGB is once again on the road. However, the circumstances that caused the issue and the expenditure of over $300 in currently unnecessary parts, not to mention 2 weeks off the road, are worthy of memorializing in the hope others can avoid the same fate.

In 2002 I purchased two non-op 1977 MGB's. After two years I had one sort of operational car. As Paul mentions the grounding strap is a bugger to attach on the gearbox when you don't have a garage and are lying on your back in the driveway. Installing a strap to the engine was the way to go.

The engine end was easy, use one of the motor mount bracket bolts. For the body end I drilled a hole in the box frame. Now comes my downfall.

Inexplicably I screwed the body end in with a small sheet metal screw. No star washer, nothing. Vaguely I recall thinking "let me just get it running and I'll come back and do it right". Never happened.

So 20 years on the screw loosened to the point the ground was lost and I'm left on the side of the road wondering what changed. Without the help of the guys above I'd still be wondering.

So the moral here is make repairs the correct way the first time. Because unless your memory is much better than mine you're asking for trouble when you least expect it.
Brian Denis

Your honesty is to be commended ... if not your assembly skills at that time :o)

Glad it's sorted.
paulh4

As a postscript , my 1980 roadster has the earthing strap attached underneath the oil pressure pipe joining union on the bulkhead with the other end attached to the nearest nut/bolt on the rear engine plate. (This is as done in the factory at the time). It has the benefit of keeping it away from the worst of the elements!
I have replaced it once in 44+ years of ownership.
Cheers
Charles


Charles9

I have not heard of or seen that before.
paulh4

Hi Paul,
I checked this against the under bonnet of a car that came up for sale a couple of years, same colour & year as mine that had been stored , unused - it was on youtube which i have kept as a record.
Cheers
Charles
Charles9

Paul,
The youtube link is :-

https://youtu.be/nEQXdr69Ebc?si=hSF5-938tU1MF49x

Cheers,
Charles
Charles9

Can just about spot it at 9:03, thanks for that and your photo. A very late change, in fact Clausager does reference it at chassis number 515195 roadster and 516743 GT in April 1980 which puts it at only 8000 or so cars from the end of production or less then 2% of the total!
paulh4

Wow! Where in mass do you live Brian? I'm Northshore Woburn. Was just wondering if you were local to me?
S

Hi S.D., I've seen your posts occasionally... always very helpful. I'm pretty sure you've responded to my tales of woe in the past.

I'm in Newburyport, about as far north as you can get and still be in Massachusetts. My usual cruises are along route 1A, 97 and 62. My cars, a 1977 MGB and a 1958 MGA, are wrapped up for the season.

I was cutting it close whether I was going to have to put them away with issues. In mid October the MGA's front right brake locked up 25 miles from home. I had to replace everything from the brake pipe split to the brake cylinders. Repair took three weeks between waiting for parts and my own inertia.
Brian Denis

This thread was discussed between 15/10/2024 and 27/11/2024

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