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mgedit
06-25-2018, 02:15 PM
I've been enjoying my 56 TR3 this summer and it has been running quite well, other than an occasional hesitation. Last week I took it to my weekly golf game and when leaving the golf course it took 4-5 seconds to start, which is very unusual. It normally starts right away. Thought I best check that out. Couple of days passed and I decided to start it up and investigate. Would not start, no attempt to fire at all. Today I started trying to sort out what was wrong. Far as I can tell, I'm not getting any spark. The spade terminal on the nylon slide in connector on side of distributor was loose (turned easily from side to side), so I thought that might be source of poor contact. Had a new one in my parts stash so swapped that out. No improvement. Next changed points and condenser and re-set gap. Still no spark. Getting 12V at both sides of coil (small connectors) and 12V at wire going to points. Coil is measuring 3 ohms across small terminals (primary circuit) and 8900 ohms (secondary circuit) between centre and both small terminals. Don't have another coil handy to try swapping out coil. Am I missing something? What else should I measure/try to identify the fault? Has me stumped. Cheers, Mike

TR3driver
06-25-2018, 02:35 PM
Turn the engine until the points are closed, and recheck the voltages on the coil pins. You should still have 12v on the wire to the harness, but close to 0.0 volts on the wire to the points.

If that looks OK, check for spark right at the top of the coil (with the high tension lead to the distributor disconnected). Sometimes rotors can fail invisibly and short the spark to ground.

mgedit
06-25-2018, 04:06 PM
Thanks Randall. With points closed, 12V on both small terminals on coil, and at nylon connector, but 0V at points pin/arm where condenser wire and wire from nylon connector join. No spark from top of coil to ground when cranked. When I was replacing parts earlier replaced rotor with new red one (same as what was there before). Cheers, Mike

bobhustead
06-25-2018, 04:21 PM
With points open, do you have power at the moving points contact arm? You might start suspecting the wire from coil to points. When the points are closed and things are normal, that wire is in dead ground and the juice would prefer that circuit to fighting the little resistance in your meter. Thus the near zero reading Randall mentioned.
Bob

TR3driver
06-25-2018, 05:39 PM
Thanks Randall. With points closed, 12V on both small terminals on coil, and at nylon connector, but 0V at points pin/arm where condenser wire and wire from nylon connector join.
Bingo! The wire from the nylon connector to the points is bad.

Its a special extra-flexible wire, because it has to flex whenever the vacuum advance moves. They do often fail by going open circuit with no external indication.

Might well be the cause of your hesitation, too. Vacuum advance moves when you step on the throttle, and could position that wire just so.

mgedit
06-25-2018, 06:09 PM
Will swap it out again, but it is brand new. Will check again for voltage to be sure. I think I have a couple more new ones in my distributer parts box. Thank you Bob and Randall.

mgedit
06-25-2018, 06:17 PM
Just measured voltages again before doing any swapping. So it was zero on the nut holding the wires to points assembly. At end of wire from nylon connector was 0.15V and also 0.15V on spring wire going to contacts. These measurements with points closed. Cheers, Mike

mgedit
06-25-2018, 07:22 PM
OK one more update. Triumph friend dropped in to say hello tonight. Told him what was happening, wondering if he might has some ideas. We checked wiring and voltages (all as I last reported) and put all back together and car fired up right away. Now I don't have any idea what solved the issue I was having. Glad it sorted itself out, but would have preferred to find and fix a specific problem. Will go for a run tomorrow and make sure things have remained fixed. Cheers, Mike

M_Pied_Lourd
06-25-2018, 07:31 PM
Oh, I hate when it fixes itself without knowing what you did ....I'm with you, I'd of preferred to find the culprit and rectified it...I would be on the edge of my seat for the first few drives...cell phone fully charged and the caa card at the ready :cool:

Cheers
Tush

bobhustead
06-25-2018, 08:07 PM
I suspect an intermittency in one of the wires from the coil to the points. You will probably find it when you drive.
Bob

TR3driver
06-25-2018, 09:36 PM
Thanks Randall. With points closed, 12V on both small terminals on coil, and at nylon connector, but 0V at points pin/arm where condenser wire and wire from nylon connector join. No spark from top of coil to ground when cranked. When I was replacing parts earlier replaced rotor with new red one (same as what was there before). Cheers, Mike

I just re-read this, and maybe I made a bad assumption. At the point where the two wires connect to the points, the post and nut are supposed to always be grounded. That is why you put the little "top hat" insulator under the point spring, and another one on top of the two wires with the crown pointing down through the wire terminals and again into the point spring.

So when testing for power at this point, check on the wire terminals, or the point spring (which is also a current conductor).

A very common mistake is to put the wires on top of the upper top hat, instead of under it. Won't run that way ...

mgedit
06-26-2018, 06:31 AM
Insulator and wires are in correct positions. Will wiggle wires a bit today and check dwell now that car seems to want to run. Cheers, Mike

sp53
06-26-2018, 10:46 AM
take a coil with you

mgedit
06-26-2018, 02:28 PM
Well the plot thickens. Went out this morning and car started right away and ran for about 2 seconds. Then back to no spark. More investigation to follow. Cheers, Mike

TR3driver
06-26-2018, 02:35 PM
Well, if you were checking voltage before at the wire terminal, rather than the nut; I'd still say it's a bad (intermittent) wire. I've also seen the ground lead (from the moving plate to the distributor body) go bad and be even harder to find. In both cases, what usually shows it up is removing one end and then checking for continuity while gently tugging on the wire.

mgedit
06-26-2018, 03:03 PM
Thanks Randall ... will try to find time tomorrow to identify the culprit. Cheers, Mike

CJD
06-26-2018, 03:07 PM
Last time I had an intermittent spark I found the nut holding the hot wire to the ignition switch had loosened. So once you clear the distributor, you might want to follow all the connections out from there.

poolboy
06-26-2018, 08:21 PM
Here's a good link you might want to save:
https://www.mgb-stuff.org.uk/points.htm

mgedit
06-27-2018, 07:03 AM
Thanks Ken. Very nice reference page. Cheers, Mike

TR4nut
06-27-2018, 08:45 PM
Take a good look at the low tension lead between coil and distributor- the wire can break but it still will look intact with the insulation. Happened to a friend of mine and gave similar symptoms.

mgedit
06-28-2018, 06:46 AM
I’m going to check all wires for continuity as part of next stage of trouble shooting. I will report what I find. Cheers, Mike

mgedit
06-28-2018, 02:52 PM
So I seem to be going again. Checked all wires and they all had continuity despite gently wiggling and tugging on them. Only small thing I noticed was that the ground wire from body of distributor to plate was very slightly damaged. Looked like insulation was pinched a bit. Sorted that out with a very small bit of shrink wrap and reinstalled everything again just like before and started right up. Still not completely certain that I've found the root cause, but good for now. See what tomorrow brings :-)

Set points at 15 thou, and dwell is 50 degrees. Read that dwell should be more like 60 degrees. Does 50 indicate a little too much gap or a bit tight? Feeler gauge seems to have just slight resistance so I thought gap was pretty close. Just curious.

Thanks for everyone's help in working through my problem.

Cheers, Mike

bobhustead
06-28-2018, 03:54 PM
Dwell is how long the points remain closed between rides up the lobes. Smaller gaps = longer dwell. I have never bothered to routinely measure dwell (even when I was a line mechanic). Slight resistance to movement of the feeler gauge is the right test.
Bob

CJD
06-28-2018, 05:15 PM
Like Bob says, dwell is how long (in degrees) that the points remain closed. The significance is that it relates to the time the coil has to fully form its magnetic field, before being forced to discharge. More dwell gives the coil more time to “charge”. Of course, at low RPM the coil has way more time than it needs. Lower dwell could become a factor at high RPM.

In your case, Mike, I would leave it at 50 degrees. As the points wear the dwell will increase on its own...unless you plan to go racing??

mgedit
06-28-2018, 09:26 PM
Thanks. Appreciate the help. Was planning to leave at 50 degrees ... strictly street use on nice quiet secondary roads usually. Cheers, Mike

mgedit
06-30-2018, 07:46 PM
Drove the car a bit yesterday. Ran great, and the ocassional hesitation I had seems to be gone too. Cheers, Mike

CJD
06-30-2018, 09:45 PM
Hopefully your once-over got all good to go for another year!