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MG MGB Technical - Best Cap and Wires?

What's the latest thinking on the best distributor cap and plug wires? I'm thinking it's probably time for me to move beyond the original style side entry cap, and I like the idea of using wires with 90 degree preformed ends for the cap end. I'm interested in reliability and long service life, not necessarily the least expensive. My engine is stock 1966, with a 25D, a Pertronix replacing the points, and a Lucas Sport coil. Any recommendations?
Terrence Goodell

If there's nothing wrong with them leave them alone. There are too many problems with replacement ignition parts these days. If you must then don't use the original carbon string which go high-resistance over time as the carbon dust migrates, get silicon-cored which are very stable, I've never had one fail, the set on the V8 have been on for over 80k
PaulH Solihull

Thanks Paul. The existing cap and wires are probably at least 20-years old. Old enough anyway that I can't remember when I got them. The cap terminals look fairly corroded, and I was experiencing misfires due to dust (carbon tracking?). Seems to run Ok after I wiped the cap out, but now I'm nervous. How corroded is too corroded, and is it OK to wire wheel the terminals?
Terrence Goodell


Advanced Distributors is all you need to know...1st class rotors with brass and cap with brass inserts and not steel...
Bob Dougherty

There is a gap between cap and rotor so there will always be burning on both. If it runs then it isn't corrosion as such, which probably wouldn't block HT anyway, just the results of arcing.

If you can reproduce misfires at a standstill then you can diagnose many HT problems with a timing light. Clip it onto the coil lead and watch for any irregularity in flashes especially coinciding with a misfire. If you are getting them then that points to coil or ignition LT problems. LT problems with the exception of the condenser should show up as a the tach needle flicking with the misfire. Condensers usually either work or not, as a quick elimination of that you can temporarily connect a second one between the coil terminal going to the distributor and earth.

If the coil lead only shows steady flashing clip it onto each plug lead in turn. If those show irregularity then it is cap or rotor. Again rotors usually break down altogether, quite soon after starting to show problems if not immediately, and can affect any plug. Cap problems usually affect a plug or plugs consistently.

When on 1 and 4 point the light at the crank pulley and watch for excessive timing jitter.
PaulH Solihull

Paul - Took me a bit of noodling, but now I understand what you are saying. The diagnostic technique with the timing light is a great idea. I'll give that a try.

Bob - Thanks for the link, and the reminder. I'd forgotten that many have highly recommended them.

Terrence Goodell

I must wholeheartedly agree with Bob. Advanced Distributors is now my sole source for ignition rotors, distributor caps, contact breaker points, and condensers. Jeff Schlemmer sells only quality stuff. As for spark plug leads, Pertronix has taken their 8 mm High Tension (HT) lead (Spark plug lead), which is designed to meet the demands of high performance engines, and now offer it with exactly the same features in 7 mm flat black, making it possible to fit state-of-the-art High Tension (HT) leads (Spark plug leads) into the Lucas distributor cap. It has two current paths for reliability and redundancy. Its primary path consists of spiral wound stainless steel alloy, while its secondary path consists of a carbon impregnated fiberglass center core. It has a low 500 Ohm-per-foot resistance. It also has silicone jackets to resist high temperatures, moisture, oil and chemicals, and an EPDM (Ethylene Propylene Diene Monomer) rubber inner insulation for superior heat resistance and prevention of arcing and voltage leaks. Fiberglass reinforcing braid is used for added strength and flexibility.
Stephen Strange

This thread was discussed between 28/09/2010 and 01/10/2010

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