Odd distributor cap wear


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Dec 13, 2021
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So i was troubleshooting a slight misfire and pulled my distributor cap and noticed brass dust all over inside the distributor. Flipped the cap over which has less than 50 miles on it and noticed what you see in the pic. At first I thought ok the rotor must be rubbing the cap and shaving off the contacts, maybe i did not push it down all the way. So i put a new cap and rotor on and with maybe 15-20 miles i am already starting to see the same issue. Took a good look at the rotor and it looks perfect on both so i cut a cap in half so i could see the clearance to the rotor and it does not come close to touching anywhere. Does anybody have any ideas what would cause this? I do have an MSD 6al on the car but i cannot imagine it is blasting the brass terminals away. This is just a parts store Standard Blue Streak cap and rotor kit. Is the cap and rotor just cheap junk? Any help is appreciated!

I think you have the wrong rotor in it. Some brands have to be matched also believe it or not.

Common mistake often boxed wrong also. If the rotor is hard to push down it is the later one. Alot of the new stuff is junk even Blue streak.
Ignition Rotors

Have a pic of the rotor off also?

I think I see a slight score mark in in the pic would be the top of the terminal. What distributor also?

I have good caps and rotors listed if needed.
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I would start out by calling MSD and telling them which of their products you have, the brand, and the type of cap and see what they have to say. To my knowledge, the brass contacts are the best for the standard points, rotor, and cap. But you have perhaps a hotter hybrid system.
Looks like the rotor is sitting too high, maybe not seated entirely. Or the cap contacts are too low. You turned your distributor into a lathe.
any chance the plastic spacer on the distributor shaft below the body has deteriorated allowing the rotor and shaft to move up and down?
The distributor is just a stock mopar electronic unit as far as i can tell, it came with the motor which is a 78 400 that i swapped into my 67 fury. All the lean burn stuff was already gone. Not sure if the distributor was different for lean burn but this unit looks like a standard electronic unit (sorry i am really a chevy guy). Yeah i may have to give MSD a call, that is what the wife suggested. The upper part of the shaft where the rotor goes has about a 1/16" of up and down play but i do not see the lower part of the shaft that goes into the engine moving at all and i have another unit from a 440 and a electronic distributor on the 318 that came out and they all have about the same amount of play on that upper shaft. That being said i cut the cap in half so i could see and even when lifting the upper shaft up it still is almost a 1/16" from contacting the cap terminals as that was my first thought was the rotor was not down far enough (i will grab a pic of this in the morning).

Here is a pic of the rotor that came with the cap in the above pics:



I would think I would see some sort of wear on the rotor if it was indeed hitting the cap terminals. I have not turned the distributor in a lathe but i can next week at work.
@halifaxhops where do you think you see a slight score mark?
@volksworld what plastic spacer are you referring to, would it be this one at the bottom of the shaft (this is the 440 unit)? If so i will pull the distributor out in the morning and take a look. Something i did notice is that the contacts on the Blue Streak cap extend past the molded plastic (lower) while the contacts on both my 318 and the old 440 unit seem to be flush with the plastic. Thanks for the replies everybody i will get this pulled out in the morning and dig into it deeper.

Later model rotor for sure. The play is the advance springs. it should basically drop on the shaft. I bet the center carbon is worn also. Look at that link I posted you will see it right away. Looks like a 303 rotor to me. is it hard to put on the shaft?
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Usually new caps have the remnants from machining which looks the same as your picture shows. I clean them up with a small blade. I would guess that didn't happen and as a result, the smaller pieces of brass fell off during operation, and appeared to be "dust".
yes thats the bushing i was referring to...
also...down in the bottom of the hole of the rotor shaft there's a C clip to hold the upper piece to the inner one that it pivots on when the timing advances....cant remember right now but i think its hidden by a piece of felt (that holds a bit of oil)
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I don't think that's wear. The tip of the rotor would be destroyed if it were hitting that hard and the burrs would be off the contact in one direction, away from the rotor's rotational direction.

I think what you are seeing is burring left over from the machining operation when the cap was manufactured. To me, those look like the typical burrs I would expect from the contacts being cut.

Can you positively say "it didn't look like that when I put it in"?

I have seen new caps with that burring brand new in the box, although usually not quite that bad.
Sounds like a good opportunity to break out the automotive stethoscope. If it's hitting those brass contacts you'd hear it on the distributor cap.
I think you have the wrong rotor in it. Some brands have to be matched also believe it or not.

Common mistake often boxed wrong also. If the rotor is hard to push down it is the later one. Alot of the new stuff is junk even Blue streak.
Ignition Rotors
Ray, your Golden Words again scintillate with the Lux Veritas! I quit buying Glue Streak off the shelf 4 yrs ago, and only buy pre-1990 stuff of that brand. Standard uses slave labor now, as so many others do, with predictable results. The New Crap doesn't fit, last or even work, FARR too often. Workers can't read, calculate, and don't care. Neither do shareholders, who are worse in all these regards.

With one of your distributors, running some 50 yr old breaker, condenser, 40 yr old cap, and rotor, home prepared 7 mm copper plug wires, amd 40 yr old Bosch platinum spark plugs, Gertrude passed Pima County AZ Emissions on her first pass yestermorn. I tuned her up last May.