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MG Midget and Sprite Technical - starter motor question

Chaps: jumped in this morning...well, actually opened the door and entered sedately, days of jumping anywhere LONG gone...pulled choke, turned key...and CLICK... There not being a tree nearby to furnish a branch to do a Basil I popped the bonnet and some fiddling later freed off the jammed motor and orf we went.
I'd like to be a bit more "professional" about it next time so question is: What size [across flats] is the square end of the motor shaft? I can take a spanner with me next time..
many thanks
David Cox

Use a small adjustable spanner: the armature end is square.
Alan
Alan Anstead

Thanks, Alan, point taken..but would still like to know size
David Cox

On my spare motor 8mm fits spot on. Which was a mild surprise - I expected 5/16" to fit, but it's too tight.
Greybeard

thanks, Mr G. I'll dig one out and add it to my on-board tool roll!
David Cox

Nie Zashta!
(Yep, I've been learning Russian)!

Actually that's a good idea. I'll put an 8mm in mine too. Although the traditional way is to pop it in gear and rock it a little bit.
Greybeard

Same has happened in the past. IIRC one end of a drum brake adjusting tool (can't remember the make, may have been a Williams) is an exact fit as it's also square.
Jeremy MkIII

Prop will probably be along and ask what a Basil is. So much for Gourmet Night and that poor MG 1100 was it?

Clare
Clare Ravenwood

Lol Clare!
Greybeard

Not an MG I'm afraid, just a plain old Austin.
Dave O'Neill 2

I mentioned this to a friend who works for JLR Heritage and when I told him that an 8mm spanner is the order of the day he spat out his coffee and immediately issued me with a yellow card for putting metric tools in my MG kit. 5/16 is the order of the day...close call!
David Cox

I know what you mean Dave. Just feels wrong somehow. I'm going to try the Whitworth spanners when I get home. Just in case.
Greybeard

Each to their own but I don't understand the joy of carrying tools and spare parts to cover unreliable parts and components - and a car that doesn't start really annoys me as it diminishes the reason for its ownership unless you like it as a static piece of art.

This type of thing promotes the idea that classics are (even more) unreliable than they actually are or need to be.

But each to their own.

Whatever floats your boat


. . . or keeps the boats' engines turning in Grey's case.
Nigel Atkins

I wonder if it has had a new starter sometime in the last 30 years or so if it was manufactured to metric sizes apart from critical bits.

Trev
T Mason

Nigel..it's a hang-over from the Boy Scouts: "be prepared".....like insurance..you hope you never need it but if you do you're glad it's there...and Trev..yep..over 42 years of ownership I have been through a couple of motors..so who knows??
David Cox

So does no-one leave the starter pinion cover on?
W Bretherton

yep..pinion cover is on, covers the 'business end' of the gubbins where it engages with the flywheel.....but the jamming is freed from the other end of the motor shaft...
Ain't it great how a "simple" question ends up generating a whole conversation-thread about all sorts of stuff?
David Cox

Yes. It sounds a through the pinion is jamming on the shaft.

If the problem recurs it is probably time to remove the starter motor and clean the pinion and shaft. A pretty good job can be done without dismantling the whole assembly by using a lint free cloth and brake cleaner.

Check the thick washer. I had this problem with a replacement starter and found that a split washer had been installed instead of a solid one and that caused the pinion to jam.

My advice would be don't oil the shaft as that can attract dirt and then you're back to square one.
Peter Blockley

David, I don't know why I asked that - brain-fade probably. I reconditioned mine about 5 years ago for the Frogeye I'm still renovating. Fortunately a friend had a Bendix spring compression tool which greatly eased re-assembly.
Bill
W Bretherton

thanks to all for input...but here's another question for the sages "out there"..
Normal operation:
1 Everything stationary; starter motor pinion at end of shaft and disengaged with flywheel. SM free to spin. Birds in tree singing.
2 Switch on ignition..engage switch to "start" position. Solenoid engages and current gets to SM.
3 SM spins freely and throws pinion into mesh. Engine gets turned over and fires up
4 Engine now spinning with pinion still engaged, solenoid de-energised and SM no longer powered so has pinion thrown out of engagement ready for the next starting cycle
BUT
If the pinion is engaged with the flywheel when the engine is stationary then presumably it has insufficient torque to turn the engine..hence the jamming situation which I encountered
SO
does this mean than while I was driving beforehand that the pinion was continuously in mesh with the spinning flywheel?

thanks again!
David Cox

AIUI the teeth are designed such that when the ring gear is exerting a force on the pinion (i.e. after engine is firing) then the pinion is thrown out of mesh.
David Smith

David, I think it is unlikely that the pinion is in mesh while the engine is running. In my experience this quickly destroys the starter motor. If you think about it, the gearing of the pinion/ring gear might be around 10/1 and if the engine is running at 3000rpm then the starter is being spun at 30000rpm.
Bill
W Dunsmore

David, when the starter has 'jammed' l think what has happened is the pinion has in fact turned from its normal rest position just sufficient to engage but without enough energy to turn the engine. You may not even hear it or notice anything if the birds are singing loudly, although typically you turn the key, there is a slight clunk noise and then it sticks. So no need to imagine it was already in mesh when the engine last turned.

Has anyone mentioned yet, but a common cause of a sticking starter is a loose or frayed engine earth strap. Easy to check a short braided cable near the front O/S steading rack mount.
GuyW

It's wise as Guy says to check the earth. That is often the culprit. The "clunk" you hear is most likely the solenoid closing which has its own body earth so is unaffected by a poor engine earth connection.

As you got it going by turning the armature by hand (or spanner) it could well be dirty or worn commutator segment(s) or carbon brushes starting to give trouble. It's not unusual, but the good news is that it is not hard to fix.
Greybeard

Thanks all for friendly input...Happy Spridgeting!
David Cox

This thread was discussed between 10/08/2017 and 12/08/2017

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