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MG TD TF 1500 - She won't start today!

Well it's the nicest fall day of the year and all the aspens are golden so we decided to take a nice ride somewhere for lunch. She ('50 TD) always starts right up and did so yesterday easily. Naturally today she will not start!
She cranks easily. Got 12.5v at battery. Have power via white wires to fuse box and at coil. Have power coming back to coil from dizzy as well. Holding hi tension cables 1/4" from spark plugs produces NO SPARK however! Checked point gap. Perfect at .015". Dizzy cap looks same as it did yesterday - perfect. Points look good. WSM gives a procedure to test voltage at the points but I don't understand their procedure.

Removed fuel line from pump to carbs. Fuel flow seems normal. Tank is 1/2 full.

It's gotta be the spark, no? Only thing I can't check is hi tension output from coil. (Archives say that is very difficult so I didn't attempt.)
So does it sound like my coil went south overnight? If so, does anyone have a cross-reference number at Napa or somewhere? Any other ideas except keep reading the archives? Winter is on the way!

Any help/advice is appreciated!
Ed
efh Haskell

I forgot to mention that I've got the type of condensor that is soldered in place so I haven't attempted to replace it.
efh Haskell

....rotor?
gblawson(gordon- TD27667)

Sounds like a rotor. I've seen it many times. The weird thing is they LOOK fine. Always carry a spare
-David
D. Sander

Hi Ed,from my experience a coil is the only thing I have had to just go dead...I had a Ford truck once that would run for a while and quit and run a little longer and quit again, this turned out to be a bad condensor, I have seen points burn to the point of not firing but a little filing always cleared that up. I would stick a spare coil on and see what happens; when I get Little-T back together I am going with electronic ignition.

Regards,
Rich
Richard Taylor TD3983

Rotor is brand new and worked fine all summer. I'll try the old one however. What can go wrong with a rotor? It just spins around in circles???
efh Haskell

Tried old rotor. Still won't start....
efh Haskell

I would like to stick one voltage meter lead into secondary output end of the coil and and the other lead to ground and see what voltage I'm getting, if any. But wouldn't 20,000 or so volts melt my meter?

I have no eversion to getting a new coil from Napa if I knew the number. Again, does anyone know a cross-reference? Or should the Napa clerk be able to match mine if I just bring it with me? Better yet, can he test it? (Obviously I've never delt with coil replacement before so sorry about the stupid questions!)
efh Haskell

Have you tried holding the high tension cable from the coil 1/4 inch from earth. If it sparks then it suggests the spark. If no spark then the coil is under suspicion. Then check the low tension voltage at the coil.
A J Clapham

One more simple test: either take the center wire off of and out of the cap, or swap and put an old wire in the coil,hold the other end close to the block/head and crank it over. You should have a good spark. This would rule out a problem with the rotor or cap shorting. Make sure the tach gearbox is not loose, swinging over and shorting on the nut/LT cable at the dizzy. "What can go wrong with a rotor?" There were thousands made in the last few years that randomly failed. They failed to insulatethe sparkl from the steel. There are some really good short videos on testing ignition systems on the Moss site, go to "restoration parts and accessories/electical/ignition/then click on the diagram of the dizzy. They may help. George
George Butz

Ed,

Your coil should read 3.2 ohms (to 3.6 ohms) or so across the terminals when not connected to anything.

The Condenser should charge when an ohm meeter is placed on it in resistance mode, until it reaches infinity. Reversing the leads should cause the meter to back down again.

My money is on the condenser failing. They do. Mine did... replacing it with a modern non-soldered unit solved my problem.

warmly,
dave

Dave Braun

Sorry Mistyped message above

Have you tried holding the high tension cable from the coil 1/4 inch from earth. If it sparks then it suggests the rotor. If no spark then the coil is under suspicion. Then check the low tension voltage at the coil.
A J Clapham

Ed, try George's test with the high voltage lead out of the cap. If you get spark you'll know that the problem is under the cap. Bud
Bud Krueger

Okay, I just ran your tests above (thanks!). I get a good 3.5-3.6 ohms accross the low tension terminals (CB to SW) on the coil. I get a spark between high tension cable and earth as I crank - sometimes! By that I mean the spark requires I actually touch earth then back the cable away for the spark to "continue" sparking. Just holding the cable 1/4" from earth doesn't always produce the spark. I'm no expert but the spark isn't what I would call "strong" when it does appear either. Again, I've tried 2 rotors with same results.

I also tested the specific gravity of the battery. It shows "good". I get 12.5v accross the battery terminals. It's old, but apparantly is good. But just in case I tried jumping it from our Ford. She just cranks but will not fire up. Exact same sound as when trying from the TD battery.

So my question is can a coil conduct current but just not be producing enough high voltage for the car to start? Do coils "wear out"? Remember I did NOT get a spark at the plugs even though rotors seem fine. Cap looks fine as well.

What next?

Ed


efh Haskell

You are getting fuel, right? I would replace the condenser and give it a try. You may want to try another coil first just to rule it out. They are easy enough to change. The fact that you know the coil is doing something, and this was a sudden failure makes me think it is the condenser.
-David
D. Sander

Again, my condensor is welded on and I am sure I'm getting fuel. To replace the condensor I would have to rebuild the whole plate. I'm not sure the replacement plate from Moss would even fit in my distributor. If not, I'ld have to buy a new distributor. Not this week... Others say the condensor never wears out. I would think if it was worn my points would be burned out but they look just like a new set I happen to have.

I just called Napa and the guy didn't know much. And the Moss "Sports Coil" lists a "push type HT connection". I have a screw type HT wire. Where does one get a "push type" wire?
efh Haskell

Dave B. You said:
"The Condenser should charge when an ohm meeter is placed on it in resistance mode, until it reaches infinity. Reversing the leads should cause the meter to back down again."

How do you connect the meter to the condenser? It has only one terminal on it. The meter requires 2 points of connection, no? Maybe I'm not understanding you. This seems true of my soldered on one and a new screw on one I have in a box.

efh Haskell

Disconnect the wire from the coil to the distributor. Put one terminal on the case, and one on the pigtail wire. Make sure the points are open, or the pigtail will ground to the case.

Changing condensers is easy. You just need to unsolder the old and add an attachement screw to the plate for the new unit. You can use a self tapping screw and a star washer to aid grounding.

warmly,
dave
Dave Braun

Dave, you have email.
Ed
efh Haskell

For the archives:
It's fixed! With the help of Mr. Dave B. (as usual). I replaced the points with new ones. The spring tension on the new ones is at least 4 times more than my old ones! My theory is the gap just would not stay what I set it at for that reason. It seems smoother and more power as well. Time will tell...
Thanks everyone for the tips!
Ed
efh Haskell

I had the same problem with my 1936 TA a few weeks ago. Had been running OK, then one day, no start. Same fix. New points. I was able to get the car started by removing the movable point and bending the spring to give more tension. It ran until I was able to get the new point set.
John Masters

John, thanks for posting this. You never know 100% on some of these "fixes" and your post reinforces it in my mind.
efh Haskell

This thread was discussed between 25/09/2011 and 29/09/2011

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