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TR6 No spark 1972 TR6

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tr6web

tr6web

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To continue from a previous post, but more description subject line... Car started fine, then just died. Got a spark tester.. no spark. Changed points, rotor arm and condenser, installed new Lucas sports coil. Even removed the distributor and cleaned it up. Still no spark. Not sure if I need to do timing, but no matter what I still should have spark, correct? I don't know what else to do other than check voltages but I'm not sure how to do that. Any advice would be appreciated!
 
Did you change the distributor cap and rotor? They can fail. I had a similar situation, and that is all it took. Make sure the new rotor has a “6” on it.
 
Check inside the distributor cap and make sure the carbon that contacts the top of the rotor hasn’t disintegrated.
 
I am not trying to impugn your wrenching skills but I have seen this happen even with people that know what they are doing if they get in a hurry. Is it possible that you have the stack sequence wrong for the low tension and condenser lead wires? We used to see a car or two come in on the hook after a home tune up with the result being no spark. First thing we would check would be that stack up sequence. It is something not discussed in the factory/Bentley manuals nor in the BMC/BMH/BL manuals for MGs either. Even the likes of Mitchell and Chilton did not have this information in the manual until 1972. See attached shot from a 1972 Chilton manual. Note that the fiber washer and spacer were switched to plastic in the early to mid seventies by Lucas.
Assy Seq.JPG
 
Checking voltages should be the first thing you do in a case like this. Probably the worst way to fix an electrical problem is to replace parts randomly.

When you say "no spark," I assume you have checked for spark at the coil output. If there is no spark there, something in the primary circuit is bad. If you have spark at that point, but none at ANY of the plugs, you have a bad high-voltage wire or connection between the coil and distributor cap. Maybe a bad rotor or the carbon contact inside the cap. Look around.

If there is no spark directly from the coil, get a cheap multimeter ($7 at Harbor Fright) and measure the voltage between the + terminal of the coil and block, ignition on. That will show if you have voltage to the coil. If that's OK, turn the ignition off, disconnect the wire from the distributor to the coil, and measure the resistance from the distributor terminal to ground as you slowly turn the engine over, manually. You should see the resistance switch between zero and infinity as the points open and close.

If that checks out, disconnect the coil completely and measure the resistance between the two low-voltage terminals--it should be 3-4 ohms--and from either low-voltage terminal to the high-voltage. That should be about 8000-12000 ohms. If something will be way outside one of those ranges, the coil is definitely bad. Even if the resistances are OK, the coil might still be bad, as high voltage does strange things that you can't discover from low-voltage measurements.

If you do this, I'll bet you find the problem in five minutes.
 
I got a voltage tester. Clip to the negative battery post. Tip to the positive on the coil. Lights up indicating power! Also lights up if I touch the lead on the distributor indicating the wire from the coil to the distributor is ok. Now what?
 
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It's hard to tell from the pic but I don't see any "wear pattern" on top of the rotor coming from the carbon button inside the distributor cap.
Look inside the top of the cap to insure the black carbon contact button is in place.
 
In your prior thread I outlined a procedure to troubleshoot this.

Don't over complicate it.
 
You can buy (or could have? bought) a set of points already assembled in correct order so they won't short out. Along with many others, I also learned the hard way about assembling the points incorrectly. The car will never start and everything checks out fine.
 
tr6web said:
I got a voltage tester. Clip to the negative battery post. Tip to the positive on the coil. Lights up indicating power! Also lights up if I touch the lead on the distributor indicating the wire from the coil to the distributor is ok. Now what?
Click to expand...
I suggested a procedure. You might want to follow the other steps I suggested.

I doubt that the coil is bad. Total ignition failure is usually something simple like a broken or loose high-voltage connection. But first you need to isolated it by simple tests.
 
Once you find the problem, why don't you pull the wires off the distributor and rotate it 180* then put the wires back. There'd be less bending at their connections if the positive was on the radiator side of the coil and the negative on the distributor side of the coil
 
Are you sure the points are making and breaking the circuit by opening that little bit. If they do not open that little bit, then you will have power where you show power--- but no spark. Sometimes the points look fine, but they have a cloud of oxidation and will not make and break the circuit. The coil creates the spark by the points closing for that brief moment and then opening.

steve
 
To reiterate:

As Elliot suggests, check the iggy switch. But you've introduced too many variables, now need to go backwards from the "no spark" at the plugs. With a test light (or better, a VOM), see if voltage is getting to the coil at the +12 side first, with the key in the run position. If 'yes' the issue is points, timing or the HT wire to the dizzy. If 'no' the problem is the wiring from there, back to the voltage supply. Is there an ignition fuse in a '72 (Been too long since I've seen one)? The switch is next. Check for voltage from the (IIRC it should be) brown wire at the switch. Voltage there means the switch is at fault. No volts and the problem is further toward the battery supply. Check to be sure the "fat" brown wire at the starter solenoid is secure. Since you've changed the oil filter, it's possible you may have inadvertently bumped or somehow loosened that. If all is good from solenoid, through the switch and out to coil, back under the hood...

With the cap off, iggy "on" and test light on the distributor side of the coil, the light should be on if points are open, off if closed (Be aware that if all that is working, the coil will "dump" high voltage to the cap as the points open, and you can get a surprise if you have body parts close to the HT lead from coil to cap!). If no light in either points condition, the voltage side of the points is shorted to ground in the dizzy. If the light stays on with points open or closed, the points are not making contact. Use some fine grit wet-or-dry sandpaper to clean both sides of the points.

If all that tests well, the HT lead to the cap is suspect first.

Hope something in all that helps.

BTW: How did you determine the engine timing after the changing of points, condenser, etc?
 
I'm a bit curious on what the dwell meter showed. If nothing else it will let you know that the low tension side of the ignition system is working and whether or not the dwell timing is correct. Granted that is operating on the assumption that the OP has a dwell meter but as far as I am concerned, if you are going to work on car with a points/condenser set up, a dwell meter should be considered a mandatory piece of equipment.
 
On my 73 there is a resistor wire in the harness leading to the coil . ---If you use a coil with an internal resistor then there will be double resistance and no spark . ---The Lucas coils are really bad about indicating if an external resistor is to be used . ---Most american coils specify " use external resistor " right on the side . --I'd try running a jumper direct from the battery to the positive terminal of the coiland seeing if you get spark
 
Thanks for everyone's tips. I was able to finally try the spark plug test..... no spark, yet there is power to the coil. I pulled the wire from the distributor that goes to the coil, inserted the spark plug, grounded it by touching the block and started the car (see photo). I even tried another distributor wire to make sure it wasn't the wire. I also tested the power points with the spark tester and still getting power. Even inserted the tester into the wire going to the positive end on the coil and it has power too (see photo). First, am I doing the spark plug test right? If so, what's next for me?

distributor1.jpg

distributor2.jpg
 
You might try replacing the coil if you have one.
 
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