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MG MGB Technical - M418 starter adjustment

My Lucas M418G starter is playing up. It was fine for about 200km but now when starting the car it is making a chattering noise, just like when the battery voltage is low although that's not the problem here. It still turns over fine and the car starts easily. Just when the starter is engaged you get this odd noise.

Garth suggested a loose wire inside the solenoid but I removed the starter and solenoid and checked it and I can't find any problem there. The solenoid is new as of a few months ago as the old one had pitted and broken contacts and wasn't engaging.

With the starter out I have tried testing it with a battery charger although this can't really supply enough current to do this successfully. I am charging up my spare battery today so I can test it.

What I did find however was the I could get the pinion to extend and stay if I gave it a little push (I had the actual motor disconnected at this point) but by adjusting the eccentric pivot I could reproduce the same chattering effect. I am wondering if perhaps I needed to adjust this after replacing the solenoid?

What is the correct/best way to do this? Energise the solenoid from a decent supply (my spare battery when charged). Then when the solenoid is energised and at the end of it's travel I pus it back towards the motor and measure the gap between it and the thrust washer? I see you also need to make sure the arrow is aligned correctlt to the marks on the body too. Could this being out of whack cause the chattering noise?

Simon Jansen

Oh, I should add I think this is actually the wrong starter for my car which is a 78B with an 18V engine. I am pretty sure this is a 418 starter though as that's the only one in the Haynes manual that they mention has the adjustable pivot pin. Is that correct? It's a bit hard to tell from the diagrams and I can't find pictures online.

Simon
Simon Jansen

Sounds like what happens to V8 starters, where exhaust heat damages the solenoid over time. You get the chattering because there isn't enough voltage left when turning over the engine to keep the solenoid operated. Initially it will still start, but it worsens over time until it won't turn over the engine. You also get the same condition if there are any bad connections at the battery, battery earth strap, engine earth strap, or in the brown circuit from solenoid to ignition switch, and the crank circuit from the ignition switch or relay to the solenoid. But if it still does it on the bench then it must be internal to the starter. It should just work, and not need tweaking other than the adjustments given in the manuals. Haynes says to set up the solenoid adjustment with a *6v* supply, if that's not an error, and it has been set correctly, then it should have no trouble at 9-10v when turning over the engine.

M418G is the pre-engaged starter used on 18G* engines, the 18V used a 2M 100. AFAIK the pinions and engagement are the same so any differences are internal and shouldn't affect how it turns over the engine.
Paul Hunt 2010

It sounds to me like a failing Bendix drive. They are basically a one way clutch using rollers to lock the drive gear when starting the engine. When the engine has started, it protects the starter by allowing the Bendix drive to be over run by the engine without doing any damage the starter. I have replaced hundreds of these over the years and it is amazing that they last as long as they do. RAY
rjm RAY

Don't have Haynes, but the factory/Bentley book has a second part to the adjustment procedure that establishes whether or not the switch contacts are functioning correctly after adjustment.
If you don't have the book - get it - maybe somebody can scan it for you - I'm not up to typing it all out just now, sorry.

FRM
Fletcher R Millmore

I have the Bentley book but it's the only up to 1974 edition so it doesn't show this starter. It definitely says M418 on the housing.

I did some more playing last night with a charged battery. The solenoid alone pulls in strongly and the motor by itself runs well. Adjusting it as per the book I can make the chattering a lot less. Basically that adjustment seems to be to set the end float between the pinion when thrown out and the thrust washer and the pinion (via the little captive ring).

By hand the one way clutch seems good and you can definitely see the solenoid spring through a small hole on the body and it is that that's moving.

I got to the point where it would pull in, chatter for a second then lock in place and run properly. By this stage my external battery was flat again. So will try again tonight.

One thing I did notice is I am getting about 1mm of movement on the pinion shaft when the solenoid pulls in. The book doesn't give any specs for such things but that seems a lot.

Battery in the car is new, solenoid is new to replace one with burnt out contacts and it was working for a few months. All cables and connections are good and tights and were made with electrical copper grease. Will measure the voltage right on the starter when I have it back in the car.

I might try to find my old dismantled solenoid and if this one keeps playing up and gets worse. I can either get a new one or maybe swap the coils over by putting my good contacts in the old solenoid if that coil is better.

I imagine though the chattering could be causing some terrible arcing of the solenoid contacts if they are opening and closing.

Simon
Simon Jansen

My Bentley is also up to 74, fourth revision, 1975. Page 295/6, plate N34.


FRM
Fletcher R Millmore

Thanks Fletcher, will have a closer look when I get home tonight. I find it hard to find things in that book sometimes. My Haynes manual is the grease covered one I use in the garage!
Simon Jansen

Most pre engagement solenoids have "two" internal circuits, one to pull the starter into mesh and one that draws less current to hold it in. This leaves more power for cranking. It could still be a faulty solenoid with the hold circuit not working or not reaching the hold contacts. Adjustment of the throw may help, I would try less pinion travel to allow the the solenoid to travel further. Denis
Denis4

Simon,

I'm posting three jpeg files (one here, others follow)of the relevent section from my Leyland manual (1972) - early car M418G Lucas. You may have this in your Haynes, but just in case....

If you need the full section, mainly removal and service/repair, let me know.

Regards
Roger



Roger T

Sorry, ignore the rh column, that is for the control unit.


Roger T

Simon,

Make that two images. I have lost count of the time spent trying to load the third. It was a graphic of the starter and components. Probably not needed but if so let me know and I'll email it.

Regards
Roger
Roger T

Hi Roger, thanks! Those are the same instructions as in the Haynes book which I used. Starter is back in the car now and it's not as bad but still chattering. I set up the end float as indicated and that still made the noise so I just tried carefully adjusting the pivot while the motor was running. I couldn't get it to stop chattering although in some places it would only do it briefly. I set it to the best position for now and will probably look for a good second hand motor to rebuild. There is a 2M100 (the correct one for my car) on a local auction site just now for $20.

Simon
Simon Jansen

Simon In your first post you say the starter was chattering on starting but now you say its chattering when running and you are "trying to adjust it while running". Thats a different thing all together.
Denis
Denis4

Chattering on starting was when in the car. Chattering on running was when I had it running on the bench. Basicaly I mean the same thing sorry, the starter motor/solenoid is chattering when it (the starter motor) is running.

When I was adjusting it I was adjusting the pivot with the starter motor running and the solenoid pulled in while the whole lot was on the bench.

I wouldn't want to be trying to adjust it under the car when the car was running :)

Simon Jansen

After I turned the computer off it came to me that was what you meant. The two circuits I spoke about in my earlier thread, both pull the pinion into mesh then the strongest one switches off to leave more power for cranking. It appears that the light hold in circuit is stuffed, so the main pull in circuit will be turning on and off. I dont think the internal wiring will be in the books. Denis
Denis4

"then the strongest one switches off to leave more power for cranking"

Not really, the strongest one switches off to stop overheating the solenoid, same as the D-type OD. The difference in current drawn compared to what is being drawn by the motor itself is insignificant.
Paul Hunt 2010

I have an M200 starter on my cars and at one time one of them started exactly the sams symptoms, i.e chattering whilst starting although the engine would start. It was the hold in circuit of the solenoid that was faulty and replacing the solenoid cured the problem. Now I know that you say you have a new solenoid fitted a few months back but could this just by chance be faulty. Perhaps you could prove this by changing the new contact assembly from the new to the old unit if you still have it and see what happens then??
Iain MacKintosh

That internal wiring is probably what Garth told me about. He mentions a wire than comes loose causing this symptom. To get the end cap off I need to unsolder the wires on the solenoid.

I did pull the old one apart to look at the contacts but didn't pay any attention to the coil wiring at the time and I am not sure I kept the bits.

Might have a go at this one. I remember a replacement solenoid wasn't expensive.

If I do will try to take pictures.
Simon Jansen

Simon I dont like mucking around with the solenoid just replace it. Many years ago I drove a tow truck after hours at a place where I was mechanic during the day and during that time attended many car fires. At least half were caused by short circuits in the starter solenoid, even while parked. Good reason for a kill switch. When I first got my "B" I could not sleep at night thinking about that old long "hot" lead running all the way under the car to a forty year old solenoid. The other fires could be divided between earthing through the throttle linkage(crook earth) and leaving the dipstick rag under the lid. As well as a few fuel leaks onto hot exhaust.

Paul The O/d is in use for long periods where the starter is only in use for (usually) seconds and if it gets hot enough to fry the windings in that short time the current draw is certainly not insignificant. I think long life and a bit more omph are both good reasons
Denis
Denis4

To my mind 18-20 amps *is* insignificant in battery load terms compared to 250 amps cranking current, it's not even that high a current in absolute terms. But we may have to differ on that. 240 watts is going to get pretty hot pretty quickly and it's heat that buggers the windings.
Paul Hunt 2010

I have a nice big red safety cut off that isolates the positive on the battery mounted on the heel board. I use that when working on the car and as an anti theft device (the alarm bypasses the switch so it always works). It did occur to me it's good that is there though in case the solenoid ever does fail on!
Simon Jansen

Right, finally sorted this. Garth was right, there is a wire internally that breaks. Here is what the inside of the solenoid looks like. You need to undo the two screws then unsolder the wires which are poked though holes in the terminals. The copper rectangle is the contact that bridges the two copper terminals in the end cap. You can see a small copper wire in the top left hand corner.



Simon Jansen

Here is a close up of the offending wire. You can see how it is spot welded to the body. What has happened is this wire has broken at the welding point. To fix it I just re-soldered it. I am not sure how long that repair will last. The wire should not move as far as I can see so the connection should be good I think. I put it back in the car and that indeed fixed it. I am getting really good at removing a starter motor and resetting the timing now!




Simon Jansen

This thread was discussed between 04/05/2010 and 10/05/2010

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