SEV no spark at points

[Rene LHD]

Good afternoon, i am working on a LHD R4 circa 1973 with SEV distributor. It was running fine until the spring on the points snapped and was resting on the main distributor body. I have replaced the points condenser and ignition coil but i still have no spark at points.
Also, which is No 1 cylinder as there are conflicting recommendations on web. is it at the bulhead end or not.

Thank you in anticipation
RENE

 

[Andy McGhee]

Rene
Number 1 cylinder is the one nearest the front of the car.
Have you checked the wire from the coil to the distributor body, and all the connections to the latter?

 

[André4Renaults]

Yes, number 1 cylinder is at the front of the car, nearest the flywheel, as explained on page 42 of the workshop manual. Remember that you might have the engine 360 degrees 'out', which might explain why it won't fire. The engine goes through TWO complete cycles for every one power stroke in each cylinder, so double check you're on the right half of the cycle. That piece of paper acting as an insulator on the side of your distributor looks decidedly dodgy too!
(I'm not implying any lack of ability, but it does happen!)

 

[Rene LHD]

Thanks gents for your replies. I will carry out these checks and report back.
Also can anyone help me identify the build date for this car, it's a R1126 252989 chassis no. Lastly, the distributor image is not one that I have posted, guess it was for illustration purposes??
Regards RENE

 

[angel]

If this is the oval plate number, car is 1974 model year.
On the terminal screw on Andy McGhee's photo there is a stack of nuts and washers; among them there is a fibre one (insulating) that must be placed first (closest to distributor body). Check also that the plastic block that holds the moving contact spring and terminal screw is intact, and that spring is not grounding somewhere on distributor body.

 

[Andy McGhee]

Thanks gents for your replies. I will carry out these checks and report back.
Also can anyone help me identify the build date for this car, it's a R1126 252989 chassis no. Lastly, the distributor image is not one that I have posted, guess it was for illustration purposes??
Regards RENE

Exactly - I happened to find an old SEV distributor in the garage, and thought a photo would be useful!
Good luck with the car.

 

[Rene LHD]

Good afternoon. Forgive me if I am repeating myself ads I thought I had posted update on Monday....
I checked the black insulator seemed OK. There was no fibre washer on the outside ,so fitted a rubber washer . Checked coil to distributor lead , seemed OK but replaced anyway.i also put another washer under condenser screw to move it away from the points , in case it was touching.I still have no spark at points. Any advice would be appreciated. Also can anyone help with where no1 cyl port on distributor cap as I forgot to image it....

 

[André4Renaults]

Let's go back to first principles to sort this. Using a decent multi-meter carry out the following tests:
1/ With the ignition switched ON, confirm that there's 12 volts at the "+" terminal of the coil. If there isn't, find out why!
2/ Whip the plugs out (it makes turning the engine easier!) select "volts" on the meter and connect it between the points wire on the coil and earth. Turn the ignition on and, using the fan belt turn the engine over. As the points open and close the voltage on the meter should alter between 12 volts (when the points are open) and zero (when the points are closed) If this doesn't happen, the coil may be at fault, although I shouldn't condemn it just yet! (I'll cover this later if we need to!)
Carry out these tests first and report back with the answers.

 

[Rene LHD]

Thank you Andre, will do and let you know
KR RENE

 

[Rene LHD]

Good afternoon Andre,. Here are the test results. 1- 11.5 volts at +ve terminal. 2- varied between 11.5 volts and 0.9volts.
Further to this I put the plugs back in , it turned over and started!!. Left it running a while and then on roadtest, it lost power like the ignition had cut out, and would not restart. After 30 minutes and retested as above with meter, same results, it then started again!!!!Drove it home and it seems fine, which is a bit maddening, as I do not know if it's fixed or not....
Do you have any further ideas or tests I can carry out and report back?
Regards RENE

 

[André4Renaults]

The coil might be dying, but that's not definitive. As it warms up it breaks down and produces less spark, hence the car not re-starting. The 0.9 volt reading should really be 0.0, so it might be worth either removing the points and trueing up the surfaces, or, if the points appear pitted, changing them.

I suggest this as your next investigation:
1/ with the plugs out, rotate the engine until the points are closed (i.e., in contact.) Now switch on the ignition and, using a PLASTIC (so it's insulated) pointer or screwdriver pull the points apart. You should see a small blue spark and a small "click" as the points are opened. If you notice a BIG FAT spark and a loud "thwack" then the condenser (sometimes referred to as the capacitor) has failed. If it has, your points will not function properly and will over-heat. Report back on this first.

2/ If the capacitor has failed (as per the above checks) change it and the points. It's a false economy to attempt to true up a set of points that have been run with a defective capacitor. Now re-set the ignition timing, remembering to set the gap first and the timing second. If your meter has a dwell angle setting you can set the points extremely accurately, but this involves quite a bit of skill!
Report back on these tests first before we condemn the coil.

 

[Rene LHD]

Thank you. Will do. RENE

 

[Rene LHD]

Good afternoon Andre. I have been working on the car today. When I got there the car started with no problem. I left it running for a while, and prepared to go on roadrest. Just as I pulled away, the car cut out and no restart.
Rechecked voltage at coil (test 1) showed 11.5v .
Checked points, as per your last post. There was a small click and small blue spark, so seems OK. I have noticed that the coil is very hot to the touch. When testing with volt meter, the points closed 12v but when open and engine still hot 11 volts.
Checked coil at small posts with ohm meter and on 200 ohm setting only registered 45-50 ohms and still hot to touch.
I hope this info helps and look forward to hearing from you. Regards RENE

 

[André4Renaults]

As I said, when the engine's off but the ignition ON 12 volts should be coming "down the line" from the battery. With the points closed that 12 volts passes through the coil, into the points and then to earth. In this position the coil is being energised. As the points open, the pathway to earth is broken and as this happens the energy in the coil is released to the plugs. From what you say your coil is in the energised state all the time-hence why it's overheating.

Another test I ought to have suggested is to see if there's resistance in the points when they're closed. To do this select the highest resistance measure the meter has & connect one end to a good earth. Disconnect the points wire at the coil and connect the other meter lead to this wire. The meter is now measuring the resistance at the points and nothing else, as everything else is disconnected. The resistance should go from NIL when the points are closed, to infinity when the points open. If you don't record these readings there's a "short" somewhere. Sorry to ask you to do more tests, but it will explain why the coil's not being switched on and off properly.

 

[JdeW]

Very hot is not good and as @André4Renaults wrote it could indeed be a short somewhere.
Normally the coil get warm under normal operation as it "shorts" aprox. 40-50 times per second.

Here's the theory of operation or as I call it elementary school electronics.
The battery voltage is much too low for a spark plug to spark. The battery voltage is therefore increased to a value of 10,000-30,000 volts using the coil, which is nothing more than a transformer.

The breaker is opened and closed by a polygonal shaft (in a four-cylinder engine this is square) with rounded corners, the distributor shaft. This is usually driven by the engine's camshaft and therefore rotates synchronously with it, at half the speed of the crankshaft. In the rest position, the stop of the breaker rests against a flat side of the distributor shaft and the circuit from the positive pole of the battery is closed by the primary winding of the coil to the negative pole (which is on the chassis). A magnetic field builds up in the coil through induction.

Ignition takes place at the moment that the breaker opens because one of the corners of the distributor shaft reaches the stop and as a result the arm of the breaker lifts (the contact points are opened). At that moment the magnetic field disappears and that causes a very fast (steep) induction current surge with high voltage that discharges over the spark plug. Between the electrodes of the spark plug this high voltage bridges a small distance through the air and that gives the ignition spark.

The capacitor plays an important role in this. Its task is threefold.

1. it absorbs the induction current surge so that no spark occurs between the contact points of the breaker. Without a capacitor the contact points would burn in very quickly.

2. the capacitor together with the self-induction of the coil (they form a so-called LC circuit) ensures an alternating current in the coil that can therefore function as a transformer: a direct current cannot be transformed.

3. the capacitor ensures the highest possible induction voltage. Charging the capacitor at the moment the contact points are opened happens so quickly (the increase is so steep) that the magnetic field of the coil collapses much faster (approx. twenty times faster) than would be the case without a capacitor. In simple terms: the power stored in the coil does not simply flow to the ground, but the coil is, as it were, sucked empty by the capacitor. This creates a much higher voltage peak on the secondary side of the coil, which ensures that a very bright spark is generated between the electrodes of the spark plug.

The high voltage is led to the center connection of the distributor with a spark plug cable, and the rotor mounted on the distributor shaft (and therefore running synchronously) ensures that the high voltage is led to the correct spark plug.

 

[Rene LHD]

Thanks gents. Not back until next week, but will update then. KR RENE

 

[André4Renaults]

This is THE best explanation in layman's terms of a car's ignition system I've ever read!

 

[angel]

Are you testing ignition coil primary circuit resistance with terminals removed? If yes, and if resistance is that high, the coil is faulty. Normal primary resistance is around 3 Ohms.

 

[Rene LHD]

Good afternoon gents. Rechecked my previous work, ie 11.5 volts at coil. Points voltage went from 12v to 0.78v open/closed. I stripped out the points again and removed the post and insulator. The insulator is a bit rough on one edge(where points have been replaced in the past,would be my guess)but otherwise seems ok. Refitted the post etc , reset the points gap. Rechecked test voltage, still 12v and 0.72v. Refitted plugs and the car started first turn..... I left it running and drove around the yard, it did not cut out. Coil now warm (not hot as previous experience). Tried several restarts and it did each time. I didn't have the time for full roadtest, so still not sure if it is fixed or not, will update after next visit.
Checking primary resistance, is that between pos and neg terminals, if its like coil off car? Will check and report next visit.
Regards RENE

 

[André4Renaults]

The primary resistance is between the two little terminals on the coil. It doesn't matter which way round you connect the meter but it DOES matter that all the connections to the car's electrics are removed from the coil before you measure the resistance. If your meter has crocodile clips at the ends it helps. The resistance reading should remain the same over time, so leave the meter connected for, say 5 minutes & note any change in the resistance. 3 ohms would be a safe reading in my opinion. The resistance between either small terminal and the H.T. wire should be much higher, of the order of 5-20K ohms. A lower reading may suggest a problem within the coil.