My experience with distributor caps has always been that at engine shutoff they are a bit too hot to hange on to for very long, although they cool fairly rapidly. On my Chrysler products with the slant six they seldom had problems, and somight be replaced once at 60,000 miles on general principles. On my Horizons and Neon they did not ever seem to develop problems. Of course, all of those caps were as close to symetrical as possible.
Plug wires were a different sory, as they usually had to be replaced a bit more frequently, I never did figure out why some failed and some didn't. I did come up with a cheaptrick for checking plugs, which is to use a DVM multimeter to measure resistance between plug top and engine block. Anything less than open circuit meant time to either clean or replace that plug.
I was a VW freak back in the 70s. The list of awesome bugs and buses I owed is now flashing before my eyes. A 65' beetle, and a 60' delivery bus that had spent its first few years as a TV repair shop runner in good old Germany gave me the best street cred that I could afford at the time. I also owned a 60' Karman Ghia, and assorted other beetles.
One thing they all had in common while I owned them was that there were a couple spare distributor caps in the glove box.
Those carbon traces were a constant problem, and since I did a lot of woods cruzin I'm sure it was worse that the average strictly street driver would deal with. Sometimes I could wipe away the dust and the engine would get better for a bit, but usually the traces were forming on hair line cracks in the Bakelite of the cap. I'm guessing running way hot... then trying to float across a huge puddle is not the best way to treat a cheap used car.
Slightly different root cause but very similar in the cap failure issue. I will say that I've not changed a distributor cap in at least 25 years...
You also reminded me of hitting the rotor and cap contacts with some emery to clean up the burning and corrosion for good measure... Ahh... The good ole days.
Ah yes........moisture in the cap. Back in the early 80's, my neighbor came knocking on my door at 7:00am looking for my help. He was late for work because his car wouldn't start. It had been raining all night and still coming down, so I suspected moisture was shorting out the distributor cap. I pulled the cap and wiped off the interior and exterior, and put it back. Engine still wouldn't start. As this Ford Fiesta was approx. 5 years old, I suspected the cap material was no longer as dielectric as when new. I pulled the cap again, took into my kitchen, and baked it in the oven at 250°F for 10 minutes. Rushed it across the street before it could cool and put it back on. Engine started right up. I told him to pick up a new cap on his way home from work that night.
(Thanks GM for keeping us entertained with your engineering blunders. BTW, thanks to ALL of them, as they keep lowering and lowering design practices!).
If the distributor cap is not simetrical (electrically speaking), as is the case with this design, it will always fail at that particular cylinder. In other words, that Cylinder will always be the weak link in the chain.
The reason for this is the bad design practices resulting from a mediocre lay-out of the engine components inside a too-tight engine compartment. Would the engine compartment have been designed with proper engineering, it woulndn't have required a flattened, side exit distributor cap to begin with...
But being that present day designs made extremely fast, by people that has very little actual experience (albeit posessing great AutoCad dexterity, that produces extremely compact-but failure prone designs!).
As for the cap and rotor design, OEM not always is the best. In this particular engine, you can replace the rotor and cap with a much better fabricated one (better materials and better overall dielectrical design) made by ACCEL, sold as a "performance" part, Part Number: 130141 "Heavy Duty".
That part will cost you 20 bucks (the garden variety, equivalent to the OEM is about 9.99). Either you can buy two of the std. ones and change them sooner,or get the performance oriented one and expect twice (or more) service time. Amclaussen.
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