![]() ![]() Now place the cap on the distributor and carefully place a Sharpie mark on the distributor body that vertically lines up with the Number One spark plug wire terminal on the cap. Now mount the rotor on the distributor and bump the engine around until the balancer displays roughly 15 degrees before top dead center (BTDC). Also make sure that the cap you are using is a true MSD distributor capwith brass terminals and not aluminum. It’s possible that the cap was improperly registered on the distributor. Next, make sure that the MSD cap is properly registered with the distributor cap pin in the slot in the distributor. Remove the rotor and lightly lube the mechanical advance mechanism to ensure it works properly. ![]() ![]() The fix for this malady is to first ensure the mechanical advance mechanism is fully functional. The real issue is that some voltage is being siphoned off to the previous cylinder in the firing order. So the plug might fire, but it will be doing so into essentially a dead cylinder. You won’t necessarily feel this as a dedicated misfire because that voltage ends up in a cylinder that is on the exhaust stroke. If the rotor is retarded enough, it might actually bleed voltage off to the previous cylinder. This requires the spark to jump the large gap between the rotor and the cap. The deposits on your cap indicate that the rotor consistently fires short of the spark plug terminal. So when the pickup triggers the coil to fire, the rotor has not yet advanced enough to line up with the terminal on the cap. In this case, the rotor is retarded in relation to the pickup. MSD has a good videoon what happens when the rotor is not phased properly. This is most commonly referred to as rotor phasing. This is a clue that the rotoris in the wrong position when the pickup aligns with the spinning pole piece and triggers the coil to fire. If you lose enough spark energy, part-throttle power will suffer and the engine will seem sluggish and unresponsive to throttle.īut what’s also interesting is the fact that this corrosion is located on the leading edge of the terminal. Then if your plug wires also have high resistance, this really can hurt spark energy. This corrosion creates resistance, which reduces the voltage that ends up reaching the spark plug. I believe that’s what we see as buildup on the edge of each terminal. But this corrosion shows up as aluminum oxide. It just doesn’t rust like iron components. You may not realize it, but aluminum does corrode. This means there will be more resistance in the high tension circuit to the spark plugs. Aluminum does not conduct electricity nearly as efficiently as brass or copper. This is an indication of an inexpensive distributor cap. Our first clue is to look closely at the spark plug terminals on the inside of the cap. So we need to discover why this is occurring. When this happens regularly, the electrical energy oxidizes the metal in the mechanical advance, turning some of the iron into iron oxide particles that collect on the inside of the cap when thrown off from the rotor. If the rotor gap is too large, often the resistance from this large gap will be greater than the resistance created to jump down to the steel rotor screws and into the mechanical advance weights in the distributor. This material is iron oxide and is the result of misfires inside the cap from errant sparks inside the cap looking for a convenient ground path.Įlectricity will always follow the path of least resistance. Most often, I see this on the inside of HEI distributors, but it can be common on any distributor. But looking more closely, I’ve seen a dark brown material coating like this before, appearing like a very fine powder. Jeff Smith: At first glance, I thought the dark area on the cap was grease. ![]() Also notice the whitish aluminum oxide deposits on the spark plug wire terminals. Our guess is that the inside of his rotor was absolutely filled with this stuff. Notice the dark iron oxide area on the inside of the cap. This is the photo of the cap that W.D sent us with his question. ![]()
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