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MG Midget and Sprite Technical - Solenoid

Ok

Loud click when ignition turned to 'start'

Battery 12.95v at rest so not the best but ok
(Charged up but still the same result)

Solenoid smacked with large spanner but to no avail

Car rocked in gear - just in case it's a jammed starter but not that

Any way of repairing a solenoid - it's a bog standard BMK1727 type, the one without the button? It looks a bit like it's 'no user serviceable parts inside'
Jeremy MkIII

I'd make sure it's the solenoid by placing a large screwdriver between the large terminals, it will put a burn mark on the screwdriver so don't use your best Snap-on one. Make sure you only connect the screwdriver between the terminals and not to ground.
R.A Davis

Also check the engine will turn by either pulling the fan belt round ( pull on the blades) or pushing it in gear (ignition off)

Have you tried 'unwinding' the starter with a spanner on the squared shaft end to disengage a possibly stuck bendix?
GuyW

Thanks both.

had forgotten about unwinding the starter.
Tried that and it seemed free. However tried rocking it in gear again and then it started. Switched if off and tried again and started again. Very strange. At least it's not the solenoid!
It did the same thing about 10 years ago so if it lasts another 10 years I'll be happy.
Jeremy MkIII

Jeremy, it will just be a bit of dirt on the bendix spiral gear just occasionally catching it enough to prevent the gear from disengaging itself. If the engine fires up the flywheel turning will kick it back out of mesh. But if the engine doesn't fire first time the gear is then already in mesh and the engine has too much inertia to get the starter to spin immediately and you get that tell-tale clunk!

PS Unwinding the starter on the squared shaft you won't actually feel that anything is sticking. The shaft will turn the spiral mesh gear, pulling the bendix back and there is very little actual resitance to this.
GuyW

Your car battery should be 12.6 at rest. If you have just charged it, it will be a little higher but should settle down to 12.6 V

When cranking the voltage should not drop below 10 V.

So your battery is fine, unless that's a typo in your post?


Chris Madge

Guy, Chris thanks for the explanations and tips. Not a typo Chris just ignorance on my part.

This morning we're back to square one. Just the clicking.
Tried Bob's test and sparks flew along with the starter engaging.
Tried freeing the Bendix again and rocking it in gear but to no avail.
So seems the solenoid is ok. As is the starter motor as it spun when the solenoid was jumped. And the battery.
So what's left? Could it be the ignition switch itself and is there a way of checking that?
Jeremy MkIII

Jeremy,
a fully charged battery could be at 12.8v or 12.9v, then allowing for error on the test meter you could get higher figures.

A good way to test for volts on a rested battery is turn the headlights on for say 20 seconds then turn them off before putting your meter on. Whatever figures you get doesn't mean the battery is good enough to start the car under stress but normally turning the key is the best real world test.

But as the car has started twice unless the battery has suddenly become weak you can perhaps say the battery seems fine - but always check all connections are clean, secure and protected, on battery, solenoid and starter plus earths of course.

Yes it could be something to do with the ignition switch though the loud click would suggest to me it possibly wasn't but you could hotwire the car to bypass it if you want to test.

I wonder if your starter solenoid is fully earthed, easy way to check is to take a wire directly from the battery earth to the body of the solenoid. If it successfully repeatedly starts up then that'd probably be it. Remember to recharge your battery after all those starts - by going for a long drive.
Nigel Atkins

Check your engine earth strap as well.
It could still be a slightly sticking bendix, or a combination of marginal issues that collectively conspire against you! sticky Bendix/ slightly low battery charge/ poor earth to chassis connection/ poor electrical connections at starter.
GuyW

Jeremy,

Shorting the solenoid only proves the starter turns - not the solenoid
Not sure what you mean by :-

'Tried freeing the Bendix again and rocking it in gear but to no avail' if it wasnt stuck ?

As you know the motor turns and the battery is OK,
as Nigel has noted check for a good earth to the solenoid - although you must have some earth present as it clicks.
Try taking a wire from the battery to the ignition start terminal on the solenoid (best pull off the original for testing) and holding it on see if that starts the car (pull off immediately if it starts ! -if so maybe an ignition switch issue.

If not your solenoid may be faulty.

R.
richard b

<<Tried Bob's test and sparks flew along with the starter engaging>>

Actually this suggests that all is well on the starter side of things and those connections, but the fault is the solenoid not switching properly. If the solenoid is clicking, then the ignition switch is working. So it's either corrosion where the fat cables connect to the solenoid ( remove, clean and reconnect) or, as Nigel suggests, the solenoid isn't earthing properly through its mounting bolts. Beyond that I suppose the contacts inside the solenoid may be suspect.
GuyW

Richard makes a good point about the solenoid I forgot to put not to rule it out and I'm a fan of Guy's combination of things together. If you have the time and inclination you could check, clean, secure, protect, repair all of the items listed, before or after finding the resolve to the issue. I think sorting just one part and leaving other parts that are weak can be a false economy and to do this at your convenience now is better than possibly later at the roadside, unless you like to wear your underpants over your trousers.

Of course it does rely on your supply of can-be-arsed which I always find to be in very low stock with me but sometimes you just have to use the last stock up and hope more will eventually arrive at some point in the future.
Nigel Atkins

Thanks again for all the help and suggestions.

Nigel, have tried earthing the body of the solenoid to the battery earth strap. No difference.
Have added an additional earth to the solenoid again without any change.
Will test the battery as you suggest and see what happens. have a spare battery so will jump it to see if that makes any difference.

Guy, will check the earth strap but it was a new one back when restored (circa 2008) so may need attention now - time really does fly!

Richard, I was referring to Guy's suggestion to put a spanner on the nut at the front of the starter (under a plastic cap) and turn to free the starter. I put it in gear and rocked the car to see if the starter was jammed and if so, free it up.

Guy,

I thought that with the sparks flying and starter engaging that meant the solenoid was performing ok but from hat you and Richard say, it may not be so. At least it's the least expensive item to replace if I have to start down that route!

Nigel, CBA is not an issue ATM as I'm peed off with the damn thing so am intent on getting it going.
It was pampered and polished for its agreed value photos on Weds and rewards me with throwing a hissy fit. Prima Donna. I've warned it that it's going to get a damn good thrashing if it doesn't start soon!
Jeremy MkIII

Jeremy,
value is all about cosmetics, hence only photos required.

CBA may well very quick empty if the car starts and be at insufficient levels to proceed further, inventory and actual physical stock are two completely different things.

The only thrashing you should give it is going down the road, and you can bump start it to do that, then get it back home, switch it off and forget about it for a while - sorted.

Any other life problems just let me know.
Nigel Atkins

Jeremy, I suggested the screwdriver across the solenoid terminals to rule out the starter being the issue. The fact that the starter spun when you did this test, suggests the solenoid or the connections at the solenoid are the issue.

Bob
R.A Davis

<<I thought that with the sparks flying and starter engaging that meant the solenoid was performing ok>>

Not necessarily. The solenoid is just a remote switch operated by an electromagnet. Power from the ignition switch when you turn it to the "starter position" operates the electromagnet and connects the power in (from battery) to the power out (to starter). When you use the screwdriver you are simply short circuiting between those terminals, by-passing the internal contacts of the solenoid.

It all points towards a solenoid issue, or connections to it, as the problem
GuyW

Thanks Bob and Guy,
after a couple of hours rummaging, I've found the original solenoid, complete with red button and am cleaning up the contacts prior to refitting it.
IIRC it was replaced as it was too rusty and would detract from the other new shiny under bonnet 'bling'.
We'll see.
It may have to wait until Monday as my daughter is home from the Lakes this weekend.
Jeremy MkIII

I had a similar problem early last year, and it indeed proved to be the new 'lucas' solenoid that I had fitted about 4 years previously.

I drilled out the 4(?) rivets holding it all together to find inside that the two main terminal contacts had a build up of rust. The studs looked like copper on the outside (where the nuts screw on), but it was obvious that they were simply copper plated steel. I cleaned the rust off and smothered them and the contactor plate with silicon grease and reassembled using M4 nuts and bolts instead of the rivets. Been fine ever since.
J Smith

Interesting J Smith. I may try your solution if the original replacement doesn't work. May try it in any case as useful to have a spare.
Jeremy MkIII

Just replaced the 'new' solenoid with the original 50 year old one - result, started first time.
Even the little red button to turn the engine over works; remarkable.
Thanks for the analysis and recommendations.
Jeremy MkIII

That's good news.
An intermittent problem like that is always difficult to trace, annoying and often contrives only to show itself at times inconvenient to you!
GuyW

I like J Smiths idea, but obviously using some BA screws and nuts, but Jeremey would have to lend me some CBA.
Nigel Atkins

Thanks Guy, yes that's usually the case. This time however it had the decency to get back into the garage before failing!
Nigel, plenty of CBA here and you're very welcome to share it 🙂
Jeremy MkIII

Jeremy,
great news about your stock of CBA, rather than having it in transit and mess up your asset movement logs I'll post the part to you - course that does require some CBA, oh dear.
Nigel Atkins

Haha!



Jeremy MkIII

This thread was discussed between 09/09/2021 and 14/09/2021

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.