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TR2/3/3A 3A Quits Running....Petronix?

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K

karls59tr

Obi Wan
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The car was running strong then suddenly it died....it would restart and run for a few blocks then die again. I nursed it along to a friends garage and checked the wiring connections to the coil and distributor and they appeared OK. I pulled the distributor cap and to my surprise saw the top of the Rotor blackened. It appears that the little carbon button and spring had disintegrated in the HT tower!The rest of the cap internals appeared fine. Fuse in the box blown as well.(what is the correct fuse 25 or 30?)
I didn't have a spare dist cap in the boot but my friend had a new dist cap for a TR6. We removed the carbon brush and spring from the TR6 cap and carefully jury rigged it into the 3A cap and cleaned up the rotor.The car fired up and idled fine and we thought it would be good enough to get me home. Car ran fine for a few blocks and then went dead again...same symptoms as before. Had to call the tow truck. I'm not sure why the carbon brush failed initially or if the Petronix has failed internally?? I'm going to install the original point set up but before I do that is there a way to test to see if the Petronix is working? Also...what would the correct resistance readings be for primary and secondary on the coil?....ohmmeter set to what scale?....electronics not my strong point. Any help most appreciated. Karl
 
Fuses in the fuse block should be only AGC 20 (if you are using modern style fuses). The 35 amp rating was in a strange, obsolete system. But since the ignition system isn't fused (originally), the blown fuse might not be related. The in-line holder under the dash can use an AGC 15 (or I find that 10 works OK as well).

Here are some basic troubleshooting instructions for the Pertronix, but they are for negative ground. If you are still running positive ground, they'll need to be modified.
https://drive.google.com/file/d/0B2...ZDU1LWI3YzQtZmUxYWZiM2JiZWVi/edit?usp=sharing

Primary should be close to 3 ohms (measured on ohms X1 scale). Short the meter leads together first, and either note the reading or adjust the zero if you have an adjustment. Secondary resistance will vary with the model & brand of the coil, but should be around 8 to 10k for the original coil. Depending on your meter, you'll probably need to select the X1000 scale. Another test would be to set your meter to its highest range, and check between any terminal and the case. That should show infinite resistance (as high as the meter will read). These are only very basic tests, they don't "prove" that the coil is good, only that it is bad if they fail. In my opinion, the best way to test is to have a spare "known good" coil that you can swap in. Coils rarely fail (although it does happen), so I would look at other things first.

For example, could the chunks from the broken button have damaged the pickup or magnets?
 
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Hi what you may have is a defective rotor. If the rotor has a rivet in the top change it out for one that does not.
Itmay have arced to GND.
 
Keoke said:
Hi what you may have is a defective rotor. If the rotor has a rivet in the top change it out for one that does not.
Itmay have arced to GND.
Click to expand...

Turns out that the aftermarket distributor cap was not the correct height resulting in the carbon button and spring in the HT tower being forced against the rotor with such force that over time the pressure against the rotor chewed up the carbon and even the plastic of the tower so there was no proper electrical contact from cap to rotor.
Replaced the cap and rotor and car runs fine. Petronix not damaged.
 
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