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TR2/3/3A 58 TR3A Coil weak? 9KΩ on the secondary with a 1968 HA12 45208A non-ballasted coil.

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J

JoeTR3A

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A friend has a 58 TR3A. He had some warm no start issues (let us not talk ethanol and heat soak). I thought possible could be the coil getting too hot increasing resistance and lowering the high volts delivered to the plugs, and adjusted the voltage regulator shutoff down a tad 1/8 turn counter-clockwise on screw thinking at high rpm could have caused too high a running voltage (this lowering was actually reversal since prior adjusted voltage regulator shutoff up opposite, 5/8 turn clockwise, according to Lucas procedure since running voltage at 3,000 rpm was way too low so battery was not charging, so originally raised regulator to 16v at 3,000 rpm as instructed by Lucas). He still had one slight warm no start since reversed a tad, but not driven much.

Yesterday tested the 1968 HA12 45208A non-ballasted coil. It was about 180°F after short ride 2 miles, mounted on side of engine, so does not say much. If he ever has a future new no warm start problem, asked him to touch the coil to see if massively hot. Checked coil readings (took several with two cheap millimeters and adjusted for calibration) and got:

2.9-3.5Ω on the primary
8.7K-9KΩ on the secondary

The secondary seems low compared to replacement DBL105 spec at 2.8Ω prim 10.45KΩ secondary, and DBL101 at 2.9Ω prim and 10.9KΩ secondary.

So it seems his coil is coming up about an Ohm and a half short on the secondary winding against replacement specs.

1.) Looking for advice. Is the coil too far out of tolerance due to low Ohms on the secondary windings that the old coil should be replaced with the DBL105? Anyone suggest or recommend that? I have no idea if this is too far out of tolerance. Or are things good to go, and do nothing?

2.) If he does replace, is it highly suggested to be better to upgrade to a ballasted coil and ballast as opposed to stock DBL105 non-ballasted?

3.) If the coil is bad, weak, would the low secondary Ohms resistance lead to higher amperage delivered and the coil getting too hot raising resistance so the high voltage jacked up coil output falls and thus no warm start (and noting running voltage off the generator is higher than battery when starting)? Am I thinking possibilities correctly or in err?

Thanks for any replies.
 
The usual failure mode of a coil is that the internal insulation breaks down, so that the secondary windings start jumping, or primary/secondary windings start shorting. It is also very common that early in the failure mode the coil will run fine cold, and begin to run badly when hot.

I cannot say what to do about the ohm readings. Other than helping to tell if your coils are broken (which yours are not from the readings), it's hard to tell anything else from ohming them. If you have doubt about a coil, it's best to swap it out and see if that fixes the problem.
 
Have you considered the condenser? I had a running issue that was caused by a bad condenser.

I got a new one from The Distributer Dr. in the UK. Seems there are some poorly made ones out there these days.

David
 
Occasionally, my tr3 has trouble starting when hot. I found that holding the gas pedal to the floor on the hot start problems helps a lot. These cars do not have accelerator pumps, so holding the pedal to the floor when starting hot only lets in more air. For sure, lift your foot once it starts. Give it a try.

Steve
 
Those resistance values are fine. Coils are not identical and I've measured ones that are well outside that range.

When coils fail, it's usually because of arcing internally at high voltages. You can't measure that with a multimeter. Coils will almost always get warm, but shouldn't be so hot that you can't touch it. The car will run fine with a "nonballasted" coil (3-4 ohms). A ballasted one will not do any better. With a ballasted coil, you MUST include a ballast resistor to bring the total resistance to 3-4 ohms, so you are just back where you started.

If you adjust the regulator, you really must do it as described in the Lucas books and shop manual. Random adjustments will just create a mess. BTW, a lot of the new, replacement regulators, especially the Lucas one, are garbage. The one I bought was misadjusted, right out of the box.
 
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