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Distributor Cap


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I was looking for a misfire and had the engine running at an idle when I noticed something that I don't recall seeing before, the distributor cap was moving about in kind of a circular motion, as the rotor went around, the cap moved outwards following the motion of the rotor. Has anyone ever had this happen? I looked at the distributor and the cap and could see no appreciable wear and it didn't seem to be particularly loose and it didn't take much pressure by hand to stop it from moving. The cap is not old but is a reproduction. I found the cause of the misfire and the car seems to run fine so it doesn't seem to be an issue but I'm sure that it's not supposed to do that.

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Tom,

Where did you get the cap ?

I bought mine at NAPA, along with the points and condenser. Still very active part numbers.

There should be a "tab" on the edge of the cap to prevent it's moving.

Like the guys here say " you know that's not right"

Mike in Colorado

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Hi, I can't remember where I bought the cap but if I had to guess I would say that it had to be from one of two places, Bob's or CARS. There isn't a lot of force there, I can stop the movement with my thumb and forefinger without applying much pressure. It would seem that I either have a poorly fitting cap, worn distributor or both. I should add that the lateral movement is quite significant and it does follow the movement of the rotor.

I think that the prudent solution would be to have the distributor checked, rebuilt, if necessary and the cap replaced. Thank you all for your help.

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Hi,

I think you're describing a sort of "hula-hoop" motion. Am I right?

There has to be an outward force being applied to the cap. All I can think of is that the rotor is touching the cap at the terminals and pushing it outwards.

Check the distributor tag and make sure you have the right distributor for your car. Who knows what may have been switched in the past? Point in case: I have a Cord distributor number-tagged as a single point unit, but with dual points inside. I have no idea who did that, why, or even how.

Then I think I'd get a NAPA cap and rotor and see if that changes things. "What you got ain't right."

--Tom

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Hi,

Another thought, if you can bear it. If the bushing supporting the distributor shaft is worn and has become sloppy, the shaft will wobble as it goes around. Given enough force, it might raise the cap out of its anchored position and make it dance. Pull the cap, grab the distributor shaft, and try to wobble it. The cure is to have the distributor rebuilt with a new proper-sized bushing installed.

--Tom

Edited by trp3141592
corrected "it's" to "its" (grammar) (see edit history)
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I was just about to suggest the worn bushing -- I had that issue on my 1927 Chevy many years ago - it still worked well after many more thousands of miles, but should have been repaired -- ultimately we rebuilt the engine and did the bearing at the same time.

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Hello again,

The motion indeed resembles that of a "hula hoop". I've held on to the bottom of the cap with my left thumb and forefinger and can feel no thrust pushing the cap sideways, I can hold the cap on centre without applying much force, I don't have to grip it tightly.

The car is in storage for the winter so in the spring I'll pull the distributor and have a good look.

Thanks again,

Tom

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Tom,

If you don't have someone nearby that can help you out, I'd be happy to assist you with your distributor issue. Let me know if I can help, feel free to contact me by email at jason@aerrebuild.com or toll-free @ 1-866-228-0218. I would have to agree with Mark also, get it taken care of during the winter and you'll be ready to go come spring. I have a lot of customers who wait till fall/winter when they park it for the winter to have me work on their starter, generator or distributor and then that gives me the time to get it done and they'll be ready for spring.

-Jason

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