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MG Midget and Sprite Technical - No Spark

After maybe 500 miles on a brand-new (old stock) set of points, she started misfiring at idle, and dying embarrassingly in the middle of Leominster. Had to cool down, it seemed, before re-starting.
Naturally I suspected an ignition problem (because it always is), and took the distributor out to have a look at the points. They were fairly shut, so I re-gapped them at 0.015 and put the distributor back in. Couldn't start the engine.

I now don't have a spark. I took plug #1 out and held its threads against a head nut, pulled the starter, and it should have sparked, is that right?

The firing order is correct, 1342 going anti-clockwise as you look. What should I check next?

It's bound to be something stupid I've done or omitted to do (because it always is).
Nick and Cherry Scoop

Hi Nick, in re-gapping the points, did you disturb the nut and insulating washers on the spring and connector post?

Our friend Bill ( who I haven't seen on here lately, I hope he is OK) used to say condenser as a more or less universal engine failure fault. Said only partly in jest I think! If the condenser has failed internally, it could short the points to earth = No spark!

Another way of checking spark is at least being generated is, with the dizzy cap off and ignition switched on, flick the points open/ closed with your thumb nail (or a small screwdriver) You should see a good fat spark. If nothing then chec the wiring connections back to the coil, (both terminals) and then check the terminals at the back of the ignition switch
GuyW

I experienced a similar [embarrassing] failure...
it turned out that the small wire inside the dizzy from the external LT terminal to points had broken inside the insulation. It looked fine just by looking and connected now and again..hence the misfire..
Dave
...also...I have had soarking plugs that would spark out side the engine but wouldn't spark under compression..insufficient HT voltage
David Cox

Thanks both. Sorry to be so long: I had to go out straight after I posted.
It'll be tomorrow now.
Nick and Cherry Scoop

Nick, haven't seen a post from you in a while! Given that you've disturbed the dist. it is either the LT connection (to the points) or insulating washer as Guy suggests, or it may be the condenser (capacitor) is failing. Check for continuity from coil to connected point with points open. If ok, check the same point is insulated from earth with points open i.e. has v.high resistance. If ok, suspect the condenser (hard to test unless you have a DMM with capacitor test).
Bill Bretherton

Look in the neighborhood of the condenser. Replace it with the old condenser and see if that does solves the problem. BT DT

Cheers

Gary
79 MGB
gary hansen

I took the cap off, switched the ignition on, then pushed the points apart with a screwdriver, bridged them, brushed them, caressed them. Nothing.

Bill, thanks for replying. While the distributor is still in place (my neck won't let me do too much twisting and squinting down there, so I usually take it out to adjust/replace things) I'd like to do the checks you suggest, but I don't understand them.
1. Continuity from where on the coil, and what's the connected point?
2. How do I check insulation from earth, of that point?

If I've broken the little brown-sleeved wire, would that also prevent your tests succeeding?

Thanks, Gary. I've dug out a spare condenser, but having gapped the points properly I'm loth to change another thing until I've tested.
Nick and Cherry Scoop

You could try with a spare length of cable connecting direct from the battery (non earth terminal) to the coil SW terminal. Then try starting. This by-passes the ignition switch and other wiring behind the dashboard so will narrow down where the fault lies.
GuyW

"If I've broken the little brown-sleeved wire, would that also prevent your tests succeeding?"
Yes Nick, all the little wires in there have to be intact
William Revit

Brilliant - thank you. Goodness knows when I'll get back in the garage: I've just taken Laura to Hereford Station - sudden need to go to London - and I'm about to start on my list.

Walk the dog is the first item. Then cut the grass.
Nick and Cherry Scoop

Nick, I mean the ignition side of the points. If not sure try both terminals. One will give zero ohms to the side of the points it's connected to (opposite the earthed side). You check insulation from earth with a multimeter (DMM) set on high ohms range e.g. 1 megohm or more. If you get zero ohms with points open there is a short to earth. Of course the earthed contact/ point/ call it what you will, will give zero ohms.
Bill Bretherton

Sorry not to have returned earlier. I have not been able to get near the car for ten days. Sad but true. However, today I checked the build-up of contacts and washers on the post, and they seem ok. Also, the brown-sleeve wire has continuity. FWIW I changed the condenser for a new one, despite my earlier reluctance.
No spark

Bill, I am far more ignorant than you believe. For example, my coil has three terminals:- a spade either side of the neck of the bottle, and the contact up inside the neck itself. Which one are you talking about, for your first test?

Nick and Cherry Scoop

Nick, I mean the spade terminal with a white + other colour wire going to the points (spade with white only should be from ignition switch). You could check for 12v at coil (either terminal with points open and ignition on. Then continuity to moving point (connected to coil) as well as checking for high resistance to earth from same contact with points open. Also check for zero ohms from coil with points closed. If all checks ok there could be a coil fault. Check from centre HT terminal of coil to earth - should be a few thousand ohms.
Bill Bretherton

Bill is very definitely the expert here Nick. But for simplicity I would start by setting your meter to DC volts - there is probably be range marked 20v or thereabouts. Then with the ignition switched on, check between one of the 2 smaller terminals on the coil and a good metal earth point on the car.

You should get 12volts or probably rather less because of losses at various connections, so maybe 8 or 10v. If you do then carry on with Bill's checks.

But if you have zero volts then the fault is 'upstream' and could be ignition switch or faulty wiring somewhere, probably lurking behind the dash! In this case, add a temporary wire between the coil terminal marked SW and the battery (not the battery earthed terminal, the other, live one - depends on whether your car is still a positive earth or if it has been updated) Then try and start the car; it should run. To stop it disconnect your temporary wire.

This will begin to narrow down where the fault lies.
GuyW

Actually, having just re-read your original message, I think that the likelihood is that when re-gapping the points, you have nudged another wire in the vicinity and you now have a different problem, a loose connection. So you cured the erratic misfire by regapping, but caused a different fault.

Most likely is one of the wires has come loose, between coil and dizzy or one of the connections at the coil. Or one of those wires has broken inside the insulation so it isn't making a contact.

Or, do you have a security cut off switch somewhere?
GuyW

I finally got into the garage for half an hour this morning.

Guy - ignition on, coil spade terminal to earth = 11.5v

Bill - continuity from coil 'output' spade to points is good. But it's good to the post as well. That's bad, isn't it?
Nick and Cherry Scoop

Nick, I presume you tested with points open? In which case you shouldn't have continuity to earth I.e. the metal post the points fix to. Check the insulating washer as Guy said previously. You might not have assembled correctly and the points (well the one connected to coil) are shorting.
Bill Bretherton

Nick, the points spring should be in contact with the two wires (condenser and the connection from the coil), but NOT to the post and the fastening nut on the top. So the wires, with their little square contact ends need to be touching the spring, but the nylon washers need to then separate the spring from both the fixed post and the nut & washer on the top.
GuyW

Yes Bill. I did both, and got continuity with the points open.
It looks rather as if an intermittent short-circuit might have been the original problem, and that I've made it worse with my re-gapping.

Rain tomorrow, but I hope I'll be back on the road again on Wednesday.
Nick and Cherry Scoop

Nick, it could be a faulty condenser - or did you say you had replaced it?
GuyW

Nick - idea
Take the cap and rotor off and take a couple of nice close up pics and we (someone) might be able to pick something
William Revit

Your comment about misfiring and having to cool down before restarting often indicates a dodgy coil. Certainly if the coil gets hot you will lose ignition with normal service resuming once it cools down. Often accompanied with burning of the electrodes inside the cap.
f pollock

Thanks again. I did replace the condenser, Guy. I have no idea what that thing does; I can see that its wire connects to the live point, and its case is earthed, so if it goes wrong, does it earth the live point?

Sorry Willy - haven't got a smartphone, and my camera battery has given up. My old phone can't get it in focus, although as I look at this, the knurled adjuster isn't bad. I'll try again.

Fergus, I will wire up another coil just in case, but it's odd that it should fail completely, even when cool, just at the moment I disturb the distributor.



Nick and Cherry Scoop

Is it touching here?

f pollock

Make sure the metal band that has the moving point attached to it is not fouling on the baseplate.
Chris at Octarine Services

Yes, I thought that too, but it's an optical illusion. The spring post is well below.

I've got the distributor out again, and tested it with the condenser released and lifted away from the baseplate. Still ringing out on the post. So it must be in the stack on the post, which I will later dismantle forensically.
Thanks Chris. I will check that too.
Nick and Cherry Scoop

Ah Nick, I've found your problem. You forgot to fit the rotary arm!. I'll get my coat.....
G Lazarus

The orange wire and the black wire usually go together on the top (outside) of the spring. Where you have it, because the insulator collar is top-hat shaped it is possible for the orange wire connection to make contact beneath the insulating collar with the base plate or the pin.

Try reassembling it with the insulating collar pushed through the black and orange wire connecting tabs before it then goes down through the spring pivot hole
GuyW

Spoiler alert - those that like to learn by experience look away.

(I know book learning is sometimes frown on but as I have this in my stock of imagines from my Driver's Handbook I'll put it up for other readers).


Nigel Atkins

Thanks Nigel.

GuyW

Should there be an insulating washer under the points cam follower? My bad picture shows the underside, and there's metal proud of the fibre, which could be dragging on the baseplate.

Nick and Cherry Scoop

Yes, I've put it back together, and levered the cam follower up off the baseplate - which incidentally makes the points contacts concentric - and the problem seems to have disappeared.

Should there be an insulator, or is the follower supposed to find this level naturally?
Nick and Cherry Scoop

See -
https://www.moss-europe.co.uk/points-set-contact-breakers-high-quality-gcs107hq.html?assoc=536600

and -
https://www.moss-europe.co.uk/condenser-lead-25d-high-quality-gsc111hq.html?assoc=534799
Nigel Atkins

Few things there ---and have been mentioned by others on here but here we go

#1-The moving arm contact point looks low compared against the stationary contact
This could be and probably is caused by the fibre washer missing off the brass post that moving arm sits down on
With the washer missing the spring arm can short out on the base plate--and will
#2-With the orange wire from the condenser fitted below the spring like that the brass terminal on the wire could easily short out on the base plate -Both wires need to be up the top on top of the spring, then the nylon spacer through them and then the nut
(Guy-Nigel)
#3-While you have the points arm out checking checking for a fibre washer, the cam lobes on the shaft look like they could do with a good cleanup--is that rust or dry grease -clean that up and a very light smear of grease on there

So ---nut off,nylon spacer out, lift the swinging arm out, clean the cam and lube it, fit a fibre washer to the brass pivot pin ,
Make sure there is a nylon spacer at the bottom of the spring locating pin,(similar to the top one and sometimes joined together as per Nigel's pic) refit the swinging arm and make sure the contacts line up, fit top nylon spacer through both the wire ends and down into the end of the spring eye, fit the nut, adjust the point gap to .015" with the fibre rubbing block right on top of a lobe on the cam-----put it back in and start it up--------Yay

Far out---3 posts while I was typing that
anyway there's the problem no washer, it needs one
William Revit

As well as the missing fibre washer (or the bottom plastic top hat washer of the joined twin set in the drawing I put up) the orange wired modern made condensers can be crap.

For those that insist on retaining CB points I'd point them towards the information and quality of the Distibutor Doctor.

Dissy Doc on condensers -
"The quality of the commonly available condensers is very poor, in terms of both the physical fit & the performance /longevity. We have recently dismantled & examined 4 examples of the orange wired versions, from 4 different factories all around the globe. All of which are readily available & prevalent in the UK. The results confirmed our suspicions & why we are having so many phone calls from owners who've fallen victim to them. Original specification Lucas condensers & ours have 3 metres of winding inside, the orange ones have between 1 metre & 1.5 metres. The internal bonding & construction also left a lot to be desired.
FIT OUR YELLOW WIRED CONDENSERS"
http://www.distributordoctor.com/distributor_condensers.htm

For Dissy Doc points -
http://www.distributordoctor.com/distributor-points.html

For Dissy Doc low tension connectors -
http://www.distributordoctor.com/low_tension_connectors.htm

For Dissy Doc caps -
http://www.distributordoctor.com/distributor_caps.htm

The all important DD (original, others do lighter weight copies) red rotor arms -
http://www.distributordoctor.com/red-rotor-arms.html

He also does advance springs and weights, baseplate, etc. and - look away now - electronic ignition (top end only not full dissy).
Nigel Atkins

To help identify the parts, Dissy Doc's -
"Lucas 423153 points with original fibre heel,so much better than plastic Standard fitment, the most popular points Lucas ever made. 18/24oz's fits all 22D, 23D , 25D distributors with the original long points pivot post pre 1973.
Also available in Cooper S 32oz points / contact breakers, specification 54413568 DSB109 uprated spring type"


Nigel Atkins

In the interest of balance -
for those that prefer driving the car to adjusting CB points for wear and at services -

http://www.csi-ignition.nl/en/about_csi/technology.html
Nigel Atkins

I will hope to wrap this up today, and perhaps report success. If I can fabricate a fibre washer, that is.
Then it will be your #1 #2 #3, Willy.
Nick and Cherry Scoop

Nick, you seem to have solved the problem. The continuity to earth confirmed there was a short and it appears an insulating washer is missing and correct re-assembly is needed. So it should be all systems go soon!
Bill Bretherton

It might be worth changing the condenser for a better one - there are a lot of "fake" electronic components on the market so presumably that can apply to ignition "condensers" as Nigel alludes to. It is in a "hostile" environment so is under a lot of stress (heat, movement, electrical).
Bill Bretherton

Success! Took me three-quarters of an hour to make the insulating washer, but that's because I only had one tiny chip of fibre, and I drilled the hole too small to begin with.

Thanks to everybody. The true value of this board shines through again: a bloke with no engineering or diagnostic instincts can be helped to carry out a sensible series of tests, to a successful conclusion, and he might EVEN begin to understand how and why it all works.

Nick and Cherry Scoop

Well done.

As Willy put, as the dissy is out, the dissy cam may need a clean and lube, and if it's not already been done a general lubrication of the dissy (or if it's a dissy that's not been used for a very long time then perhaps also first a small squirt of a good releasing/penetrating oil "through the hole in the contact breaker base through which the cam passes".

From the Frogeye Driver's Handbook -
(be careful with the oiling/grease/lubricating - oil is light oil like 3 in One Motor Oil (20 SAE))

"Distributor Spindle: Lubricate the distributor bearings by withdrawing the moulded rotating arm from the top of the distributor spindle and carefully adding a few drops of oil round the screw exposed to view. Take care to refit the arm correctly by pushing it on to the shaft and turning until the key is properly located.

Distributor Cam: Apply a trace of engine oil to the distributor cam. Be careful not to let any oil or dirt reach the contact breaker points.

Distributor Automatic Advance: Remove the distributor cap and add a few drops of engine oil through the hole in the contact breaker base through which the cam passes."
Nigel Atkins

This thread was discussed between 21/05/2019 and 05/06/2019

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