Electrical Mystery. Wits End

[PaulCox]

Hi All,

My 1956 TE20D stopped running for no apparent reason in August last year. I have spent ridiculous hours trying to fix what I now know to be an electrical problem and one that appears to be completely weird.

Just for the record, new points, rotor arm, distributor cap, high tension leads, start initiator, ignition switch plus the coil is tested and sound. I have the full manual and have run the tractor for 24 years so I'm not a newbie. I think it unlikely that I'm doing something completely stupid. ;-)

I've read numerous articles and watched YT videos until I'm square eyed.

I now have good spark to earth over about a centimetre from the coil's high tension lead.

However once that high tension lead is fitted to the centre of the distributor cap, the spark disappears somewhere on turning over and does not spark the plugs at all!

So close but so far.

The new quality multimeter confirms continuity from the four distributor terminals to the spark plug electrodes as well as continuity back to the coil from the centre of the cap.

Has anybody any idea what on earth (I guess it must somehow be a earthing problem) is going on within the cap and how to fix it?

The grass is now so high I can't see the topper!

Thanks in advance,

Paul

 

[pomester]

Hi All,

My 1956 TE20D stopped running for no apparent reason in August last year. I have spent ridiculous hours trying to fix what I now know to be an electrical problem and one that appears to be completely weird.

Just for the record, new points, rotor arm, distributor cap, high tension leads, start initiator, ignition switch plus the coil is tested and sound. I have the full manual and have run the tractor for 24 years so I'm not a newbie. I think it unlikely that I'm doing something completely stupid. ;-)

I've read numerous articles and watched YT videos until I'm square eyed.

I now have good spark to earth over about a centimetre from the coil's high tension lead.

However once that high tension lead is fitted to the centre of the distributor cap, the spark disappears somewhere on turning over and does not spark the plugs at all!

So close but so far.

The new quality multimeter confirms continuity from the four distributor terminals to the spark plug electrodes as well as continuity back to the coil from the centre of the cap.

Has anybody any idea what on earth (I guess it must somehow be a earthing problem) is going on within the cap and how to fix it?

The grass is now so high I can't see the topper!

Thanks in advance,

Paul

Continental engine?
Problem seems to isolate to the rotor. Is it turning with the distributor? Defective? Making contact with the post in the cap? Is there continuity from the outside to the inside of the cap at the coil wire position?

 

[PaulCox]

Continental engine?
Problem seems to isolate to the rotor. Is it turning with the distributor? Defective? Making contact with the post in the cap? Is there continuity from the outside to the inside of the cap at the coil wire position?

Thanks Pomester.

It's the Standard engine being 1956.

The rotor arm is new and spins with the distributor. As far as I can see the timing is still correct but that I believe should be irrelevant to the lack of any spark at the plugs.

If "the post" means the carbon type sprung connector in the centre of the distributor cap it is definitely connecting as I can see slight rotational wear on the centre of the rotor arm proving connection.

As for your last question, I have just been out to check. There is no continuity from the outside of the cap to the coil wire position.

It is such a mystery. All relevant parts that are not new been cleaned thoroughly and, where appropriate, sanded to ensure good contact. I have also lightly sanded any new parts that may have have resistant covering in some form. The faces of the contact breakers and the terminals within the distributor cap for example.

 

[pomester]

Thanks Pomester.

It's the Standard engine being 1956.

The rotor arm is new and spins with the distributor. As far as I can see the timing is still correct but that I believe should be irrelevant to the lack of any spark at the plugs.

If "the post" means the carbon type sprung connector in the centre of the distributor cap it is definitely connecting as I can see slight rotational wear on the centre of the rotor arm proving connection.

As for your last question, I have just been out to check. There is no continuity from the outside of the cap to the coil wire position.

It is such a mystery. All relevant parts that are not new been cleaned thoroughly and, where appropriate, sanded to ensure good contact. I have also lightly sanded any new parts that may have have resistant covering in some form. The faces of the contact breakers and the terminals within the distributor cap for example.

I was thinking of continuity from where the coil wire pushes into the cap to the carbon contact inside the cap where the rotor contacts. I have never heard of such a failure, but you have ruled out common failures.

 

[PaulCox]

I was thinking of continuity from where the coil wire pushes into the cap to the carbon contact inside the cap where the rotor contacts. I have never heard of such a failure, but you have ruled out common failures.

Again thank you. I appreciate your thoughts.

It is a very strange situation.

 

[Charles in Aus.]

A long shot , look carefully at the connections at the side of the distributor, particularly the insulating washers . These break down and become fragile enough to break when knocked . This will ground any spark generated .

 

[PaulCox]

A long shot , look carefully at the connections at the side of the distributor, particularly the insulating washers . These break down and become fragile enough to break when knocked . This will ground any spark generated .

Thank you Charles but the insulating washers are functioning correctly. It appears to be something after the spark is generated and has entered the cap.

 

[olddavid]

You didn't mention changing the capacitor. If it is shorted you won't get a spark. When you checked the coil did you let the points fire it or just touch voltage to the coil lead? Using a voltmeter check the voltage from the coil/distributor lead to ground. With the points open you should see the battery voltage (or maybe half if there is a resistor in the circuit). With the points closed you should see no voltage. I know this is obvious, but is the rotor turning i.e. has the cam gear failed?

 

[PaulCox]

You didn't mention changing the capacitor. If it is shorted you won't get a spark. When you checked the coil did you let the points fire it or just touch voltage to the coil lead? Using a voltmeter check the voltage from the coil/distributor lead to ground. With the points open you should see the battery voltage (or maybe half if there is a resistor in the circuit). With the points closed you should see no voltage. I know this is obvious, but is the rotor turning i.e. has the cam gear failed?

Thanks olddavid,

The condenser/capacitor is new.

The coil was checked firstly by using an ohmmeter across the terminals which produced a reading of 2.7 ohms which is the specification for that Lucas coil. Secondly spark via the HT lead from the coil to earth was obtained both by manually opening the points by hand turning the distributor and also by letting the battery crank it over.

I will pass the voltmeter over it all yet again but it is producing spark at the coil. It just seemingly gets lost somehow in the cap.

The rotor arm is new and turns as it should do.

Paul

 

[olddavid]

The condenser/capacitor is new.

The coil was checked firstly by using an ohmmeter across the terminals which produced a reading of 2.7 ohms which is the specification for that Lucas coil. Secondly spark via the HT lead from the coil to earth was obtained both by manually opening the points by hand turning the distributor and also by letting the battery crank it over.

I will pass the voltmeter over it all yet again but it is producing spark at the coil. It just seemingly gets lost somehow in the cap.

The rotor arm is new and turns as it should do.

You are very welcome. Sounds like you have covered everything except the cause. I'm at a loss.

 

[Duner Wi]

IMO, It just about has to be rotor arm or cap. I had a rotor arm fail once.

 

[PaulCox]

Thanks for the " it sounds like" I have covered everything and that you are at a loss. Both comments are helpful in that it is confirmation that I've done the right thing so far.

Such a mystery.

 

[PaulCox]

IMO, It just about has to be rotor arm or cap. I had a rotor arm fail once.

You are of course correct. I'll borrow a rotor arm that is working from somewhere and trying the old cap I replaced. Thanks.

 

[J.Wondergem]

Thanks for the " it sounds like" I have covered everything and that you are at a loss. Both comments are helpful in that it is confirmation that I've done the right thing so far.

Such a mystery.

Did you check where the wire goes thru the distributor case for a short. Also clean your points with a file, then a dollar bill or such. I bought new points that wouldn't work until I did that. Sorry if you did all this and I missed that part.

 

[504]

It has to be a problem between the cap tower and the the terminals, so a bad tower contact or the rotor is not close enough for a spark to jump back to the rotor. I think you have covered all of the bases except the one that doesn’t work

 

[PaulCox]

Did you check where the wire goes thru the distributor case for a short. Also clean your points with a file, then a dollar bill or such. I bought new points that wouldn't work until I did that. Sorry if you did all this and I missed that part.

Thanks. All done I'm afraid.

 

[Jim L WA]

That spark from the coil wire either isn't getting to the rotor due to an open, or it's going straight to ground (distributor shaft) due to a defective rotor.
Let us know what you eventually find.

 

[PaulCox]

That spark from the coil wire either isn't getting to the rotor due to an open, or it's going straight to ground (distributor shaft) due to a defective rotor.
Let us know what you eventually find.

Thank you Jim.

I certainly will post the solution when I find it.

I am indeed going to have to assume that either the new rotor arm or the new distributor cap is faulty in some way. I now intend to borrow both items from a guy "up the road" who has a working petrol TE 20.

My appreciation extends not only to you but of course also to the other posters. I have nobody with any technical knowledge around here to chew the problem over with so this forum has been very helpful.

Fingers crossed.

Regards,

Paul

 

[Boss Hog]

If you have spark going into the distributor cap but not back out, It has to be an issue with the cap or rotor.

I know you said the cap was new. But I'd suggest replacing it again. Maybe put the old one back on just for a test run.

 

[Ericp351]

Hope Boss Hog, above, nailed it for you, especially if spark test was blue! IF a "sissy yellow" at 1/4" can be weak coil, et cetera. Sounds like you know same.