It may be something that is particular to the 258 I-6 I have never heard of...
I don't do many I-6 engines, and virtually no AMC engines at all, so I'm not up to date on all the quirks they have.
It very well could be the distributors checking out if several of you have the same noise.
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I've only seen one distributor gear loose a tooth, and it had a bubble in the casting...
I've seen things like guys using roller cams and not using bronze distributor gears, I've seen the wrong drive gear put into an engine, I've seen badly worn gears eat new cams because the builder was too cheap to buy a new gear....
The list goes on, but none of that would apply to you, I wouldn't think...
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Test #1
Grab the rotor, and turn it both directions, back and fourth.
The advance head will turn some if it is working, but you will feel spring pressure.
What you are trying to determine is if there is any Free Travel, (or slop) in the gears.
If you can move the rotor nose more than the thickness of your thumbnail doubled, with NO resistance, It's time for a new distributor gear.
Two Thicknesses of your thumbnail at the rotor nose, with NO resistance, and the gears fail.
New gear is about $25 from the mail order places.
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Test #2
Mark the #1 plug wire tower on the distributor base, then bump the rotor around until the rotor points at it.
Align the timing marks.
Pull the distributor, and inspect everything.
If you have more than about 0.025" play in the up and down movement of the shaft in the housing, the distributor fails.
New precision shims are required, and they are hard to find. About $1 each if you can find them.
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Test #3.
Hold the distributor gear firmly, and try to turn the rotor, first one way, then the other.
(if you use vice grips or a vice, keep in mind that gear is cast iron, and very fragile)
If the rotor can't be turned, the advance head is not working, and the distributor will need to be rebuilt or replaced.
Rebuild only costs for bad parts and for a good quality synthetic high cling, high pressure grease...
Unless you break something or loose small parts.
Tiny clips and hidden locking devices abound in the motorcraft distributor, and finding a single small part for one is virtually impossible.
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Test #4
Connect a host to the vacuum advance, and draw a vacuum.
See if the advance plate (has the pick up coil attached to it) moves, and if so, does it move the entire length of free travel of the vacuum advance arm.
Does it return all the way back to full rest when the vacuum is removed.
If it fails either one of these tests, the vacuum canister must be replaced.
$13 to $45 depending on what canister you have, IF YOU CAN FIND ONE AT ALL...
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Test #5
Hold the lower part of the distributor housing solidly.
Move the distributor shaft back and forth.
If there is any perceivable movement, the lower bushing is worn out.
No replacement available, and takes special equipment to remove old one correctly.
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If you decide to rebuild your distributor, make sure you mark the rotor nose position on the drive gear before you disassemble it.
Gear timing is important.
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For $45 you can exchange your distributor for a fresh rebuild with all new wear parts at Advanced Auto Stores.
NAPA has rebuilds for about $100.
I understand that Mopar (the dealership) sells BRAND NEW distributors for about $90.
Some of the guys here can give you a web site that has new parts for about 20% off, straight from the factory...
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Good luck, Aaron.
"I Have The Body Of A God... Buddha"
